Recent Advances in Cation-Engineered A<sub>3</sub>BX<sub>6</sub> Metal Halide Perovskite for Enhanced Radiative Transition

Recent Advances in Cation-Engineered A₃BX₆ Metal Halide Perovskite for Enhanced Radiative Transition

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Xin Zhou¹, Hang Yin¹^,²^,³^,^*, Qinhua Wei¹, Da Chen¹, Dongfeng Xue⁴, Tönu Pullerits², Junsheng Chen³^,^*, Laishun Qin¹^,^*

Research. Vol 9 Article ID 1281

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Research. Vol 9 Article ID 1281

• REVIEW ARTICLE •

Recent Advances in Cation-Engineered A₃BX₆ Metal Halide Perovskite for Enhanced Radiative Transition

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Xin Zhou¹, Hang Yin¹^,²^,³^,^*, Qinhua Wei¹, Da Chen¹, Dongfeng Xue⁴, Tönu Pullerits², Junsheng Chen³^,^*, Laishun Qin¹^,^*

Affiliations

¹College of Materials and Chemistry, China Jiliang University, Hangzhou 310018, China.

²Chemical Physics and NanoLund, Lund University, Lund 22100, Sweden.

³Nano-Science Center and Department of Chemistry, University of Copenhagen, Copenhagen 2100, Denmark.

⁴Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen 518110, China.

About Author:

^† These authors contributed equally to this work.

Published: 2026-05-20 doi: 10.34133/research.1281

Outline

Abstract

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A₃BX₆ perovskites, a family of vacancy-ordered structures, exhibit diverse luminescence behaviors upon photon, electron, and high-energy excitation, primarily originating from intrinsic self-trapped excitons or dopant-induced electronic transitions. Upon B-site cation engineering, ns² cations tune intrinsic luminescence, whereas transition-metal and rare-earth dopants activate characteristic d–d, d–f, and f–f transitions, enriching A₃BX₆ optical diversity. The tunable crystal structure and electronic configuration endow A₃BX₆ perovskites with exceptional versatility for photoluminescence, electroluminescence, and scintillation applications. This review systematically elucidates how B-site chemistry modulates the structure–property–application relationships in this material family. P-block B-site A₃BX₆ perovskites exhibit high photoluminescence efficiency, broadband emission, and strong ultraviolet absorption, enabling applications in high-sensitivity photodetectors (1.23 × 10¹² Jones), information encryption, and white light-emitting diodes. In comparison, rare-earth-based A₃BX₆ perovskites enable high-efficiency electroluminescent devices, featuring deep-blue light-emitting diode with an external quantum efficiency of 7.9%. Moreover, they exhibit superior scintillation performance, including high x-ray light yield (88,800 ph/MeV), low x-ray detection limit (63 nGy/s), and notable γ-ray response under ¹³⁷Cs excitation (47,000 ph/MeV; 4.0% energy resolution). These insights highlight the pivotal role of B-site cation engineering in tailoring luminescence mechanisms and enabling multifunctional A₃BX₆ perovskites for photonic and radiation applications.

Cite this Article

Xin Zhou, Hang Yin, Qinhua Wei, Da Chen, Dongfeng Xue, Tönu Pullerits, Junsheng Chen, Laishun Qin. Recent Advances in Cation-Engineered A₃BX₆ Metal Halide Perovskite for Enhanced Radiative Transition[J]. Research, 2026 , 9 (5) : 1281 - . DOI: 10.34133/research.1281

Full Text

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Introduction

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Radiative transitions, as the core mechanism of energy release in quantum theory, not only elucidate light–matter interactions but also enable breakthroughs in optoelectronic conversion, high-energy scintillation imaging, and quantum light sources, bridging photophysical mechanisms and practical applications [1]. Both scintillation and luminescence possess cross-domain similarities in photophysical mechanisms, particularly in excitation modalities, radiative decay pathways, fluorescent spectral range (ultraviolet [UV] or visible), energy conversion and migration process, and charge carrier dynamics [2,3]. More recently, metal halide perovskites (MHPs) have emerged as potential luminescent scintillators, leveraging their superior photoelectric properties for applications spanning photoluminescence (PL), electroluminescence (EL), and radioluminescence (RL) [4–7]. For example, the applied research for CsPbX₃ centered on the properties of PL and EL prior to 2015, while a breakthrough emerged in 2018 with its RL application in x-ray and γ-ray detection as efficient scintillators [8,9]. Following these breakthroughs, it has been increasingly recognized that high-energy scintillation performance is highly sensitive to compositional tunability, where cation substitution directly influences crystal structure, electronic configuration, and defect landscape, thereby modulating light yield (L.Y.), energy resolution (E.R.), and time response [10]. Thus, the spotlight has gradually connected application demonstrations with cation-engineered strategies, which is crucial for tailoring the electronic structure, regulating radiative transitions, and ultimately improving the scintillation performance of MHPs.

To mitigate the toxicity of Pb²⁺, as well as the radiation sensitivity and poor stability of CsPbX₃ [11], lead-free A₃BX₆ MHPs (strictly speaking, A₃BX₆ compounds are perovskite-derived structures [12]; however, they are discussed here within the framework of MHPs) are priorities for potential applications(Fig. S1) in anticounterfeiting, light-emitting diodes (LEDs) [13,14], photodetectors [15], and x-ray or γ-ray detection [16,17], due to their tunable electronic structure [16,18], highly tolerant crystallographic lattices [19,20], low phonon energies [21,22], and functional luminescence [19,23]. Recent advancements in A₃BX₆ systems have expanded the elemental scope across the periodic table, encompassing A-site cations (in blue), B-site cations (in green), halide anions (in yellow), and dopant ions (in espresso), as systematically summarized in Fig. 1. Importantly, the selection of B-site cations governs the electronic and structural characteristics, serving as a pivotal determinant for tuning luminescent behavior and functional performance through strategic doping engineering. According to the periodic table (Fig. 1), chemically accessible B-site cations in A₃BX₆ systems are classified; the B-site host engineering can be grouped into 3 categories: P-block elements, rare-earth (RE) elements with empty f orbitals (RE³⁺: Sc³⁺, Y³⁺, and La³⁺. It should be noted that La³⁺ has empty 4f orbitals, whereas Sc³⁺ and Y³⁺ lack f orbitals. For consistency, both cases are collectively classified as “empty-f” systems in this work.), and trivalent lanthanides (Ln³⁺, which are divided into light REs and heavy REs) with f orbitals. Accordingly, this review highlights the B-site cation-centered categorization of A₃BX₆ MHPs and explores their functional applications.

The Luminescence Mechanism of Host and Dopant Engineering

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Intrinsic luminescence

Substituting Pb²⁺ with lead-free cations to form A₃BX₆ reduces the Goldschmidt tolerance factor, driving a structural transition from a 3-dimensional ABX₃ to a zero-dimensional (0D) A₃BX₆. This dimensional change results in distinct electronic structures and offers opportunities for tuning structure–property relationships, particularly via symmetry control and orbital interactions. The crystal structure of A₃BX₆ with the C2/c space group features alternating octahedra with 2 distinct tilt angles, due to the different 2 independent site occupations of A cation [24]. The low charge symmetry in 0D A₃BX₆ MHPs favors the charge localization in both the ground and excited states, further affecting the formation of self-trapped excitons (STEs) and second-order Jahn–Teller distortion [25]. In general, this distortion in A₃BX₆ is derived from lone-pair electrons of ns² cations, where the antibonding orbitals formed between B-site cation and X-site anion can hybridize with the unoccupied p orbitals of the cations.

Unlike CsPbX₃ perovskites, where intrinsic luminescence primarily arises from band-edge exciton recombination (Fig. 2A) [26], A₃BX₆ MHPs crucially exhibit intrinsic STE emission leading to large Stokes shifts and broad emission spectra [27]. According to the self-trapping criterion, which is expressed as Eq. (1) [25]:

E st = W 2

(1)

where W represents the bandgap width and E_st is the self-trapping energy, which can be calculated using Eq. (2) [25]:

E st = E free − E trap

(2)

where E_free represents the free exciton energy and E_trap represents the STE state energy. Compared with 3D ABX₃, the 0D A₃BX₆ structure exhibits more pronounced local lattice distortion and stronger lattice relaxation, which lowers the energy of the E_trap. As a result, E_st increases and more readily satisfies Eq. (1), thereby facilitating the formation of STEs. In addition, the emission energy can also be described by Eq. (3) [28]:

E PL = W − E b − E st − E d

(3)

where E_b represents the exciton binding energy and E_d represents the lattice distortion energy. Compared with APbX₃, A₃BX₆ exhibits larger E_st and E_d, which results in E_PL < E_g. Consequently, this leads to a larger Stokes shift and effectively suppresses self-absorption.

Under high-energy excitation such as x-rays and γ-rays, energy deposition occurs through multiple processes (Fig. 2B) including the photoelectric effect, Compton scattering, and subsequent electron–hole pair generation [29]. Different types of high-energy radiation interact with materials through distinct mechanisms, resulting in different energy deposition characteristics. X-rays in the kiloelectronvolt range primarily deposit energy via the photoelectric effect, whereas higher-energy γ-rays mainly undergo Compton scattering, often accompanied by photoelectric absorption or pair production, leading to more spatially distributed energy deposition and differences in carrier dynamics and scintillation behavior. High-energy radiation generates ions and core-excited electrons, giving rise to a cascade of secondary electrons. It is particularly noteworthy that the lower-energy segment of these secondary electrons is most efficient at producing the low-lying excited states responsible for luminescence [30]. As a result, the scintillation superiority of A₃BX₆ MHPs is characterized by low self-absorption, high photon output efficiency, and broad spectral response compatible with photomultiplier tube or silicon photomultiplier [31,32]. However, the isolated octahedra in 0D A₃BX₆ MHPs are susceptible to point defects or heterogeneous interactions, causing energy disorder that suppresses emission [33,34]. Hence, the STE emission could be improved by dopant-related luminescence.

Dopant-related luminescence

To enhance the photoelectric properties of A₃BX₆ MHPs, B-site dopant engineering has emerged as an effective strategy for band structure modulation, which can be divided into 4 categories (Fig. 2C to E):

1.	ns² cations as B-site dopant. Incorporation of ns² cations into the A₃BX₆ host induces the modified lattice distortion, via size mismatch (ionic radius disparities causing local strain), lone-pair effects (asymmetric coordination distorting [BX₆]³⁻ octahedron), and charge redistribution (polarizable ns² electrons altering electron density and bond lengths), thereby promoting STE formation and efficient broadband emission [35]. Most ns² cations used as dopant in A₃BX₆ are summarized in Fig. 1, highlighting P-block elements (e.g., In, Sb, and Bi) into yellow dashed borders and Ln with empty f orbitals (e.g., Sc, Y, and La) into green dashed borders.
2.	Transition-metal cations as B-site dopant. Incorporated transition-metal cations in A₃BX₆ can be summarized in dual luminescence regimes: One is as B-site luminescent center ions (e.g., atomic-like ionic d–d transitions) with sharp emission lines, and the other is STE emission (Fig. 2C). Herein, Mn²⁺ (3d⁵), Mn⁴⁺ (3d³), and Cr³⁺ (3d³) exhibit distinct d–d transitions governed by their crystal-field environments [36–38]. The Mn²⁺ typically dominates an orange–red broadband emission (550 to 650 nm) originating from ⁴T₁ → ⁶A₁ transition (Fig. 2D), which is enhanced by electron–phonon coupling in weak octahedral fields. In contrast, Mn⁴⁺ (²E → ⁴A₂) and Cr³⁺ (⁴T₂ → ⁴A₂) emit narrow deep-red (630 to 650 nm) and tunable red to near-infrared (NIR) luminescence (650 to 800 nm), respectively, owing to spin-orbit or vibronic coupling within rigid and intermediate octahedral sites [39–41]. In addition, the incorporation of Ag⁺, Cu⁺, and Pt⁴⁺ can enhance the lattice distortion to facilitate the formation of STEs, further improving the efficiencies of PL and RL [42–45].
3.	Ln³⁺ with f orbitals as B-site dopant. The incorporation of Ln³⁺ into the A₃BX₆ lattice (A₃BX₆:Ln³⁺) is facilitated by their ionic charge compatibility with the host B-site cation, enabling isovalent substitution without introducing extrinsic charge defects [46]. In addition, the superiority of A₃BX₆:Ln³⁺ arises from the unique shielding effect of the 5s²5p⁶ subshell in Ln³⁺, which confines f–f or d–f transitions within the large bandgap of the host matrix, thereby enabling tunable luminescence pathways via energy-level modulation [47]. This strategy not only preserves the intrinsic electrostatic balance in A₃BX₆ but also modulates the luminescence dynamics based on the localized 4f electrons of Ln³⁺. As illustrated in Fig. 2E, such intrabandgap engineering with different Ln³⁺ as B-site luminescent center enables characteristic f–f transitions (e.g., Tb³⁺) [48] or d–f charge–transfer transitions (e.g., Ce³⁺) [49]. The energy transfer (ET) efficiency between these pathways can be optimized by controlling the Ln³⁺ doping concentration and local coordination environment. Specifically, ET or defect-state coupling activates dual-mode emission in A₃BX₆:Ln³⁺, coexisting with broadband STE emission [50]. By tailoring the B-site dopant composition and concentration, the dual-mode emission can be further tuned to match the spectral sensitivity of photodetectors (e.g., photomultiplier tube or silicon photomultiplier), further improving the scintillation performance, such as L.Y., E.R., and time response. The distinct combination of tunable luminescence, structural stability, and radiation responsiveness positions A₃BX₆ MHPs as highly versatile materials for optoelectronic and scintillation applications. Recent work focusing on B-site scalable synthesis, dopant–host matching, and interface engineering will be essential for advancing their practical implementations.
4.	ET processes induced by single or codoping. Upon incorporation of luminescent ions into the A₃BX₆ lattice, their emission can arise not only from direct excitation of dopant-specific energy levels but also from ET from intrinsic emissive states of the host lattice. Such ET processes can be broadly classified into 3 categories: STE to Ln³⁺, STE to transition metal, and Ln³⁺–Ln³⁺. In vacancy-ordered A₃BX₆ MHPs featuring isolated [BX₆]³⁻ octahedra, ET between intrinsic emission and dopant activators can be consistently rationalized within a Förster–Dexter framework [51,52]. The key criterion for distinguishing Förster resonance ET (FRET) from Dexter ET lies in their characteristic transfer distances. FRET originates from long-range Coulombic dipole–dipole interactions and can operate over distances of approximately 1 to 10 nm without requiring wavefunction overlap, whereas Dexter ET is a short-range electron exchange process that relies on direct orbital overlap and therefore becomes effective only at subnanometer distances (<1 nm) [53]. In A₃BX₆ systems, the isolated arrangement of [BX₆]³⁻ octahedra leads to increased effective donor–acceptor separations compared to more strongly connected structures. As a result, STE–Ln³⁺ and Ln³⁺–Ln³⁺ ET are predominantly governed by FRET, which is predominantly mediated by dipole–quadrupole and quadrupole–quadrupole interactions, while dipole–dipole coupling is typically much weaker. In contrast, STE–transition metal ET is more likely dominated by Dexter exchange interactions because transition-metal d–d excited states are spin- and parity-forbidden, efficient sensitization typically requires short-range exchange coupling at subnanometer distances, as evidenced in 0D isolated octahedra halides, where ET occurs exclusively via Dexter interactions between adjacent donor–acceptor pairs [54]. Thus, the isolated [BX₆]³⁻ octahedral geometry in A₃BX₆ directly governs the effective donor–acceptor separation and, consequently, the energy transfer efficiency.

In addition to the forward energy transfer pathways, thermal back-transfer represents a ubiquitous quenching channel in A₃BX₆ systems [55]. When the excited-state energy levels of dopant activators are energetically close to those of the intrinsic emissive states (e.g., STEs or defect-related states), reverse ET from the dopant back to the host lattice can be thermally activated [56]. This process is typically governed by an Arrhenius-type behavior and becomes increasingly significant at elevated temperatures or under sustained excitation, leading to reduced emission intensity, shortened lifetimes, and compromised operational stability [56]. Owing to the strong localization of excitons and the discrete energy landscape imposed by isolated [BX₆]³⁻ octahedra, A₃BX₆ materials are particularly susceptible to such thermally assisted back-transfer processes, which may coexist with nonradiative relaxation and defect trapping to collectively limit luminescence efficiency [57]. Consequently, suppressing thermal back-transfer through energy-level engineering and structural optimization is crucial for achieving high-efficiency and stable emission in A₃BX₆-based optoelectronic and scintillation applications.

Concentration quenching effect

In doped A₃BX₆ systems, the emission intensity typically increases with dopant concentration at low levels and decreases rapidly after reaching the critical quenching concentration (q_c). Compared with 3D ABX₃ and double-perovskite A₂B(I)B(III)X₆ systems, A₃BX₆ generally exhibits a higher q_c, typically around ~5 to 15 mol% for Ln³⁺ or transition-metal dopants, indicating a stronger tolerance toward heavy doping [32,58,59], which is higher than ABX₃ and A₂B(I)B(III)X₆ [60,61]. Time-resolved PL measurements further elucidate the underlying dynamics. When the dopant concentration is below q_c, the emission lifetime remains nearly unchanged, indicating that radiative recombination dominates the emission process. In contrast, once the dopant concentration exceeds q_c, the average lifetime decreases markedly, suggesting the emergence of dopant-related nonradiative energy-loss pathways [62]. The concentration-quenching behavior in A₃BX₆ can be analyzed in terms of possible quenching mechanisms. Exchange interactions are generally negligible because of the relatively large separation between dopant ions, while the limited spectral overlap between emission and absorption bands excludes reabsorption as the dominant mechanism. Therefore, multipolar-interaction-assisted energy migration is considered the primary origin of quenching [63].

This process can be well described by the Yokota–Tanimoto model, which assumes that excitation energy migrates among luminescent centers and is eventually trapped by nonradiative quenching sites, leading to the reduction of emission intensity and lifetime [64]. The isolated [BX₆]³⁻ octahedra in the vacancy-ordered A₃BX₆ framework further suppress long-range energy migration, accounting for the relatively delayed concentration quenching observed in this system [65]. In contrast, the continuously connected octahedral networks in ABX₃ and A₂B(I)B(III)X₆ are more favorable for rapid energy migration, making concentration quenching more likely to occur at much lower dopant concentrations [65,66]. It is precisely this synergistic effect of structural isolation and strong exciton localization that enables A₃BX₆ to maintain relatively high radiative efficiency at elevated dopant levels and to exhibit markedly delayed concentration quenching behavior.

The Potential Application of A₃BX₆ MHPs

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Stability and application potential

To evaluate the practical potential of A₃BX₆ materials, their stability under various environments, including moisture, high temperature, and high-energy irradiation, has been systematically examined. Under humid conditions, some A₃BX₆ compounds undergo structural phase transitions; however, unlike the typically irreversible transformations observed in ABX₃ perovskites, these transitions are often reversible and can be restored by treatment with polar solvents. The associated changes in PL enable potential applications in moisture sensing, anticounterfeiting, and information encryption.

Owing to their relatively rigid lattices, A₃BX₆ compounds generally exhibit excellent resistance to thermal quenching. For instance, Rb₃InCl₆:Sb³⁺ maintains stable emission up to 500 K [67], while Cs₃GdCl₆:Sb³⁺ retains 82.4% of its room temperature (RT) emission intensity at 150 °C [22]. This behavior originates from the 0D isolated [BX₆]³⁻ octahedral framework, in which thermal expansion is mainly accommodated by interoctahedral spaces and the relatively soft A-site sublattice, thereby preserving the local coordination environment of the emissive centers. Moreover, relatively high phonon energies and thermal activation barriers (e.g., 33.0-meV phonon energy and 51.3-meV activation energy for Cs₃GdCl₆ [22]) further suppress nonradiative relaxation processes.

In addition, the isolated octahedral framework effectively limits the diffusion of irradiation-induced defects, while the rigid lattice and localized excitonic emission enhance defect tolerance. As a result, A₃BX₆ materials display remarkable radiation stability. For example, Rb₃InCl₆:Sb³⁺ shows nearly unchanged RL intensity up to a cumulative dose of 561.6 Gy [68], whereas Cs₂NaLuCl₆/Cs₃LuCl₆:Sb³⁺ maintains stable RL output even at doses as high as 1,000 Gy [69], highlighting their robustness in high-energy radiation environments.

Applications of photoexcitation and electrical excitation

Building upon the abovementioned optical and electronic advantages, such as reversible phase transitions, tunable luminescence, and B-site elemental diversity, A₃BX₆ MHPs exhibit great potential in a range of PL and EL applications. In addition, the structural isolation of A₃BX₆ enhances exciton binding energy, effectively suppressing exciton dissociation and free carrier generation at RT [70]. Moreover, the flat conduction band (CB) and valence band (VB) for A₃BX₆ MHPs lead to large carrier effective mass, further promoting exciton self-trapping and broadband luminescence efficiency [71–73]. These features render A₃BX₆ MHPs particularly suitable for use as phosphors and active layer in thin-film LED devices.

Under UV excitation, the photogenerated carriers formed in A₃BX₆ MHPs can be driven by an external electric field to convert optical signals into electrical signals, enabling their application in photodetectors. For photodetectors, detectivity is a key performance parameter (Table 1), which is expressed as Eq. (4) [15]:

D = R 2 qI dark

(4)

where D represents the detectivity, R represents the responsivity, q represents the elementary charge, and I_dark represents the dark current per unit area. Currently, the highest sensitivity of detectors based on A₃BX₆ MHPs has reached 1.48 × 10¹³ Jones [15].

Furthermore, the photogenerated carriers yield an emission wavelength spanning from 300 to 1,000 nm without the application of an external electric field. PL quantum yield (PLQY) is a key parameter for evaluating emissive efficiency, as shown in Eq. (5):

PLQY = N em N abs

(5)

where N_em and N_abs represent the number of emitted and absorbed photons, respectively. Although visible-emissive A₃BX₆ MHPs can achieve PLQY approaching 100% [74] and even reach 93.2% in nanocrystals (NCs) [50]. The PLQY of NIR-emissive A₃BX₆ can reach 87.4%.

Relatively, the reversible hydration/dehydration between A₃BX₆ and A₂BX₅·H₂O has been actively explored for application in NIR emission, information storage, and anticounterfeiting. Moreover, the phase transitions in A₃BX₆ compounds often involve changes in crystal symmetry and optical properties, enabling tunable emission color or intensity. Notably, the NIR-emissive PLQY of A₃BX₆ MHPs after phase transitions has been reported to exceed 75% [75].

In contrast, EL differs in that it generates photons through the injection and recombination of electric-field-driven electron–hole pairs. In EL devices, external quantum efficiency (EQE) is a critical parameter (Table 2), given by Eq. (6) [76]:

EQE = η out ⋅ η r ⋅ γ ⋅ PLQY

(6)

where η_out is the light outcoupling efficiency, the η_r is radiative recombination efficiency, and γ is exciton formation efficiency. As the active layers in thin-film LEDs, A₃BX₆ MHPs have demonstrated that a maximum EQE can reach 7.9%, which is the highest efficiency among metal halide deep-blue LEDs so far [13,14].

Application of x-ray excitation

In scintillators, the majority of light emission originates from electronic transitions induced by energetic electron impact, which, in some respects, resembles the electrical excitation processes in LEDs [30]. Consequently, high-performance x-ray detector materials must simultaneously possess a high effective atomic number (Z_eff) and mass attenuation coefficient (μ/ρ) to ensure efficient x-ray absorption within limited thicknesses [77]. The total μ/ρ can be described by Eq. (7) [78]:

μ / ρ = τ / ρ + σ / ρ + κ / ρ + σ R / ρ

(7)

where τ/ρ is the contribution of the photoelectric effect, σ/ρ is that of the Compton effect, κ/ρ is that of pair production, and σ_R/ρ is that of Rayleigh scattering.

In the photoelectric effect regime (<100 keV), the mass attenuation coefficient approximately scales as Eq. (8) [79]:

μ / ρ ∝ Z eff n E 3

(8)

where n ranges from 3 to 4, indicating a strong dependence on atomic composition and photon energy. A₃BX₆ MHPs inherently possess the high Z_eff and μ/ρ due to the presence of heavy elements at both A- and X-sites, as well as their tunable composition through B-site doping.

In addition, 3 key performance metrics for x-ray detectors include L.Y., limit of detection (LoD), and spatial resolution (f) (Table 3). The L.Y. is defined as Eq. (9) [80]:

L . Y . = η ⋅ E dep W

(9)

where η is the energy conversion efficiency, E_dep is the energy deposited by x-rays, and W is the average energy required to generate one photon. Recently, the reported A₃BX₆ have demonstrated a value of L.Y. as high as 88,800 ph/MeV under 50-keV x-ray excitation [31], significantly outperforming conventional scintillators, such as NaI:Tl (~41,000 ph/MeV) and CsI:Tl (~60,000 ph/MeV) [81].

A high L.Y. enhances signal output under low x-ray dose, improving the signal-to-noise ratio (SNR) and contributing to superior detection sensitivity. For estimating the practical sensitivity, LoD is defined as Eq. (10) [82]:

LoD = 3 × σ bg S

(10)

where σ_bg is the standard deviation of background noise and S is the slope of the signal response to x-ray dose. As is known, LoD as low as 63 nGy/s has been reported, highlighting the excellent detection sensitivity of A₃BX₆ scintillators [83].

In general, a combination of high L.Y. and low LoD is highly desirable for low-dose x-ray imaging applications. As for spatial resolution, it is commonly evaluated using the modulation transfer function (MTF), defined as Eq. (11) [84]:

MTF f = M output f M input f

(11)

where M_output(f) and M_input(f) represent the contrast of the output and input signals, respectively, at a given spatial frequency. All inorganic A₃BX₆ MHPs have demonstrated the spatial frequency of 26.4 lp/mm at an MTF of 0.2. This recorded f value of A₃BX₆ MHP demonstrates greater potential than that of current commercial scintillators [68].

The application of γ-ray excitation

Beyond x-ray applications, A₃BX₆ MHPs also demonstrate considerable potential in γ-ray detection. The total μ/ρ for γ-ray photons is described by the same physical formalism as that for x-ray photons. Relative to x-rays with photoelectric effect, Compton scattering and pair production become increasingly dominant at γ-ray energies (>100 keV). Therefore, as candidates of γ-ray scintillators, the modified A₃BX₆ MHPs require not only high ρ and Z_eff but also high L.Y., fast response, and superior E.R. (Table 4).

The E.R. is a critical parameter for evaluating a scintillator’s ability to discriminate between γ-ray energies, and its value is defined as Eq. (12):

E . R . = FWHM E γ × 100 %

(12)

where FWHM is the full width at half maximum of the full-energy peak and E_γ is the energy of the incident γ-ray. A smaller E.R. value corresponds to superior detector performance and enables more accurate identification of γ-ray sources [85]. Up to now, the maximum L.Y. of A₃BX₆ scintillators has achieved 47,000 ph/MeV under ¹³⁷Cs γ-ray excitation with a good E.R. of 4.0% [32]. Compared to commercial scintillators (Table 5), their performance still differs from that of commercial scintillators.

In general, A₃BX₆ MHPs feature flexible B-site composition, tunable luminescence, and good scintillation performance under high-energy excitation. These attributes endow them with great advantages for multifunctional applications in PL/EL devices, as well as x-ray or γ-ray detections, highlighting their potential as a new generation of luminescent scintillators enabled by B-site compositional engineering.

The Categories of Cation-Engineered A₃BX₆ MHPs

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By engineering host and dopant cation, the radiative transition mechanisms of A₃BX₆ MHPs can be tailored, enabling diverse carrier dynamics and performance to meet the demands of potential applications in PL, EL, and high-energy photon detection. In this section, we focus on 6 categories of A₃BX₆ MHPs classified on the basis of B-site cation engineering and highlight their corresponding luminescence mechanisms and applications.

A₃InX₆ type MHPs

As one of the P-block cations, In³⁺ has emerged as a promising candidate for B-site host composition in A₃BX₆ (i.e., A₃InX₆) MHPs because In³⁺ exhibits good chemical stability and structural compatibility, a tunable electronic structure, and unique luminescent properties (such as intrinsic luminescence, water-driven luminescence, and pressure-driven luminescence) [23,71,86]. The A-site cations in the majority of A₃InX₆ MHPs are predominantly composed of the inorganic alkali metals, such as Cs⁺, K⁺, and Rb⁺ (Table 6). Notably, a water-driven strategy effectively induces intrinsic luminescence by incorporating H₂O into the lattice, converting A₃InX₆ into A₂InX₅·H₂O (Fig. 3A) [21,87,88]. However, such a phase transition may lead to structural instability and disrupt the electronic band structure, ultimately resulting in degraded device performance or even device failure. To manage the structural transformation of A₃InX₆ MHPs, synthesis conditions must be carefully controlled in humid environments with a polar solvent. For instance, using methanol favors the formation of pure A₃InX₆, whereas hydrochloric acid promotes the coexistence of A₃InX₆ and A₂InX₅·H₂O (Fig. 3B and C) [89]. Upon hydration, the [InX₆]³⁻ octahedral framework evolves into low-symmetry [InX₅OH₂]²⁻ dramatically modifying carrier recombination and intrinsic luminescence [87]. For example, Cs₃InBr₆, which exhibits STE emission (Fig. 3D) [71,90], transforms to Cs₂InBr₅·H₂O with RT phosphorescence (Fig. 3E), allowing reversible water sensing: The dehydrated powder exhibits yellow luminescence when dispersed in tetrahydrofuran, with its emission undergoing a distinct chromatic transition to red upon reaching a water content of 0.025% (v/v) (Fig. 3F) [78]. Under high pressure, the lower-symmetry [InBr₅OH₂]²⁻ octahedra undergo a secondary phase transition that activates mechanoluminescence (Fig. 3G) [23]. Together, the water- and pressure-driven effects in A₃InX₆ MHPs endow their intrinsic luminescence with multifunctionality.

Although the intrinsic luminescence for A₃InX₆ MHPs supports good PL applications, their PLQY remains low, primarily due to the parity-forbidden transition [91]. To improve this, as described in the “Dopant-related luminescence” section, researchers have incorporated ns²-typed dopants into A₃InX₆ hosts. Most efforts have focused on Sb³⁺, Bi³⁺, and Te⁴⁺, which introduce new electronic states that break the forbidden transition and enhance PL properties [87,92,93]. Upon Sb³⁺ incorporation, A₃InX₆:Sb³⁺ exhibits 3 different absorption bands: the ¹S₀ → ³P₁, ¹S₀ → ³P₂, and ¹S₀ → ¹P₁ (Fig. 4A) [94,95]. The emission for Cs₃InCl₆:Sb³⁺ has been ascribed to the STE state based on the excited-state absorption of Sb³⁺ from ³P₁ to higher-energy states by femtosecond transient absorption spectra [21]. Although the ¹S₀ → ³P₁ and ¹S₀ → ¹P₁ transitions exhibit distinct excitation energies, the excitons generated by both processes ultimately relax into the same STE state, resulting in emission (Fig. 4B) [96]. According to the similar luminescence mechanism, K₃InCl₆:Sb³⁺ displays dual emission peaks at 505 and 555 nm, with distinct decay lifetimes observed for these 2 emission bands, indicating the existence of 2 STE emission (Fig. 4C) [97]. In addition, Sb³⁺ imparts high resistance to thermal quenching to the material, and the Rb₃InCl₆:Sb³⁺ is applied for high-temperature white LED with exceptional thermal quenching resistance up to 500 K (Fig. 4D) [67].

In contrast to the bright emission observed in A₃InX₆:Sb³⁺ MHPs, Cs₃InCl₆:Te⁴⁺ remains negligible PL at RT [88]. However, the Te⁴⁺ doping strategy of water-driven phase transition induces bright-yellow luminescence in A₂InCl₅·H₂O (A = Cs⁺ and Rb⁺) [88,92,98,99]. One application is a promising platform for anticounterfeiting with ethanol-sensitive structural transformation between Cs₂InCl₅·H₂O:Te⁴⁺ and Cs₃InCl₆:Te⁴⁺ (Fig. 4E) [88]. The other application is visual temperature monitoring through the color-changing temperature indicator light in ratio mode, with luminescence color transition from orange–red to white (Fig. 4F) [92]. However, PL vanishes from RT to 480 K due to phase transition to Rb₃In₂Cl₉, limiting its applicable temperature range [98]. The Bi³⁺ doping strategy in Cs₂InCl₅·H₂O induces a phase transition similar to that observed with Te⁴⁺ doping, which extends the luminescent temperature window to 300 to 460 K (Fig. 4G and H) [93].

Beyond ns²-typed dopants act as sensitizers, transition-metal cations and Ln³⁺ are regarded as effective alternatives through ET process [20], the STE–transition metal ET is typically governed by Dexter exchange interaction [100], whereas STE–Ln³⁺ transfer mainly occurs via dipole–dipole interaction [101]. For example, in Cs₃InCl₆:Sb³⁺,Mn²⁺, ET from STEs to Mn²⁺ facilitates simultaneous green STE emission and Mn²⁺-derived red emission (Fig. 5A). The white LED with Cs₃InCl₆:Sb³⁺, Mn²⁺ achieves higher color rendering index (CRI = 85.5) and correlated color temperature (CCT = 6,452 K) than that of Cs₃InCl₆:Sb³⁺ (Fig. 5B) [102]. Similarly, Cs₃InCl₆:Sb³⁺,Ln³⁺ (Ln³⁺ = Nd³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, and Yb³⁺) leverages ET from STE to Ln³⁺ to achieve NIR luminescence (Fig. 5C). Notably, Cs₃InCl₆:Sb³⁺,Nd³⁺ exhibits both green and NIR emissions, while Cs₃InCl₆:Sb³⁺,Eu³⁺ exhibits excitation-wavelength-dependent luminescence due to the absence of ET between STEs and Eu³⁺, enabling anticounterfeiting applications (Fig. 5D) [50]. In addition, introducing an ET pathway between Bi³⁺ and Mn²⁺ in Cs₂InCl₅·H₂O:Bi³⁺,Mn²⁺ enhances its originally weak emission by 60-fold (Fig. 5E) [103]. These strategies highlight the synergistic potential of codoping and structural engineering to modulate luminescence in A₃InX₆ MHPs for multifunctional optoelectronic applications.

Apart from their application of PL and EL, A₃InX₆ MHPs have also been explored for scintillation applications. The emerging studies highlight their immense potential in this field. For instance, the L.Y. of Rb₃InCl₆:Sb³⁺ NCs exhibit 1.65 times higher than that of Bi₄Ge₃O₁₂ (BGO) under x-ray excitation, reaching 15,500 ph/MeV (Fig. 5F). Composite films fabricated with polysulfone and Rb₃InCl₆:Sb³⁺ achieve a spatial resolution of 18.5 lp/mm at an MTF of 0.2, showcasing promise for bioimaging applications (Fig. 5G). Radiation resistance is another critical parameter for scintillators [68]. Rb₃InCl₆:Sb³⁺ retains 85% of its initial RL intensity after 30-min exposure to a dose rate of 5.2 mGy/s and maintains its initial RL intensity even at cumulative doses of 500 Gy_air under a high dose rate of 0.5 Gy/s (Fig. 5H and I) [65,68]. These results underscore the outstanding radiation hardness of In³⁺-based MHPs and their potential for x-ray imaging. However, their performance under γ-ray irradiation remains unexplored, necessitating further investigation to unlock their full capabilities in high-energy radiation detection. This pioneering work positions In³⁺-based MHPs as promising candidates for next-generation scintillators, bridging the gap between optical excellence and functional radiation detection.

A₃SbX₆-type MHPs

P-block metal ion Sb³⁺ can not only act as dopant in enhancing the luminescence in A₃InX₆ MHPs but also serve as the B-site host composition to construct A₃SbX₆ MHPs. However, all-inorganic A₃SbX₆ faces the challenge of low PL efficiency, primarily due to crystal defects, which act as multiple nonradiative recombination centers [104,105]. For instance, K₃SbCl₆ NCs exhibit a broad STE emission centered at 440 nm (FWHM = 102 nm); through the optimization of the synthesis temperature, the maximum PLQY reached 22.3% (Fig. 6A) [104]. However, the presence of defects leads to poor optical properties in materials synthesized at RT, resulting in limited research on all-inorganic A₃SbX₆ compounds.

Compared to all-inorganic A₃SbX₆ MHPs, implementation of the metal complexes as the A-site to construct A₃SbX₆ organic–inorganic hybrid perovskites (OIHPs) can substantially strengthen perovskite framework robustness and lattice coherence, thereby enhancing charge carrier mobility through optimized defect configurations and radiation hardness [106–108]. For example, [Na(DMSO)₂]₃SbBr₆ demonstrates a broadband emission with a remarkable Stokes shift of 200 nm and a PLQY of 60%. The measured electrical–optical–electrical (EOE) frequency response yields a 7.2-MHz bandwidth, which enables an 81.6-Mbps data transmission rate using orthogonal frequency-division multiplexing (Fig. 6B and C) [109]. Similarly, [C@Cs]₂CsSbBr₆ (C = 18-crown-6) exhibits a broad orange emission (1.3 eV; FWHM = 0.35 eV) under 365-nm excitation. Its temperature-dependent PL lifetime yields a thermal sensitivity coefficient (α) of 0.04 °C⁻¹, significantly surpassing conventional thermoluminescent materials (α = 0.005 to 0.03 °C⁻¹) (Fig. 6D), highlighting its potential for high-sensitivity thermal imaging applications [110].

In addition, the incorporation of organic cations imparts structural flexibility and dynamic characteristics to the crystal lattice, providing enhanced freedom and pathways for exciton migration and recombination, thereby improving luminescence efficiency [111]. Notably, Sb³⁺-based OIHPs achieve a record PLQY of up to 100% (Fig. 6E) [74]. Relative to their inorganic Sb³⁺-based MHPs counterparts, Sb³⁺-based OIHPs exhibit broader Stokes shifts. For instance, [C₅mim][Mim]₂SbCl₆ ([C₅mim]⁺ = 1-pentyl-3-methylimidazolium; [Mim]⁺ = N-methylimidazolium) demonstrates a Stokes shift of 335 nm, significantly larger than those of other Sb³⁺-based OIHPs such as [primim]₃SbCl₆, [PMA]₃SbBr₆, and [DphgH]₃SbCl₆ ([primim] = 1-propyl-3-methylimidazolium, [PMA] = phenylmethylammonium, [Dphg] = N,N′-diphenylguanidine) [112–114]. This phenomenon arises from the disruption of supramolecular interactions within imidazolium-based groups, which triggers pronounced anionic lattice distortions [115]. Intriguingly, certain OIHPs exhibit stimulus-responsive luminescence, enabling advanced applications in information encryption. For example, [DPA]₃SbCl₆ (DPA = dipropylamine) enables a dual-mode encryption–decryption process mediated by ethanol exposure: Encrypted information remains invisible under ambient and UV light due to the inherent transparency of SbCl₃, while decryption is achieved by spraying with a [DPA]Cl ethanol solution to generate fluorescent [DPA]₃SbCl₆ under UV illumination. Subsequent methanol treatment quenches the emission for re-encryption, followed by dissolution recrystallization to restore fluorescence for secondary decryption (Fig. 6F and G) [116].

While most organic A-site cations primarily enhance luminescence efficiency by introducing structural flexibility and modulating carrier recombination without altering the intrinsic luminescence mechanism, certain organic cations, such as Bzmim⁺ (Bzmim = 1-benzyl-3-methylimidazolium), fundamentally modify the optoelectronic behavior. When Bzmim⁺ occupies the A-site to form [Bzmim]₃SbCl₆, it undergoes phase transitions analogous to those observed in In³⁺-based MHPs [21,87], albeit through distinct pathways. In In³⁺-based MHPs (e.g., Cs₃InCl₆), phase transitions involve the replacement of a CsCl unit by H₂O under humid conditions, accompanied by O²⁻ substituting Cl⁻ in the [InCl₆]³⁻ octahedral framework [21]. In contrast, the phase transition in [Bzmim]₃SbCl₆ is driven by the extraction and reinsertion of [Bzmim]Cl within the [Bzmim]_n−3SbCl_n structure (Fig. 7A) [117]. This structural reorganization induces tunable luminescence: The emission difference between [Bzmim]₃SbCl₆ (λ_em = 525 nm) and [Bzmim]₂SbCl₅ (λ_em = 600 nm) arises from a coordination-induced redshift in the halide–metal charge transfer within the [SbCl_n]³⁻ⁿ complexes [118]. This structural reorganization-induced color change can be applied to information encryption. For example, the word “disagree” written on paper was encrypted and required decryption using specific [Bzmim]Cl solution concentrations, thermal treatment, and UV observation (Fig. 7B) [117]. In addition, leveraging the low melting point and thermally responsive luminescence of [Bzmim]₃SbCl₆, direct laser writing on paper coated with this material enabled reversible information writing and erasure through localized melting and luminescence modulation (Fig. 7C) [118]. A₃SbX₆ MHPs also show promising application in scintillation. Abovementioned [Bzmim]₃SbCl₆ generates a single radiative center at 540 nm with an L.Y. of 24,600 ph/MeV (Fig. 7D). When integrated into [Bzmim]₃SbCl₆@PMMA film scintillator fabricated through this strategy enables noninvasive internal imaging of earphones, demonstrating a high spatial resolution of 8.3 lp/mm (Fig. 7E and F) [119]. In addition to the reported 0D A₃SbX₆ MHPs, [SbI₆]³⁻ isolated octahedra tend to form higher-dimensional architectures (3D and 2D) when constructing OIHPs, while also finding applications in scintillation detection. X-ray detectors fabricated using 2D FPEA₃SbI₆ (FPEA = 4-fluorophenethylammonium) exhibit a LoD of 0.123 μGy/s and a spatial resolution of 1.59 lp/mm for imaging applications [120]. Similarly, 3D [Mor]₂RbSbI₆ (Mor = morpholinium)-based detectors achieve exceptional sensitivity (1.09 × 10⁴ μC·Gy⁻¹·cm⁻²) and an ultralow detection limit of 3.1 nGy/s [105]. In contrast, the 0D Gua₃SbCl₆ (Fig. 7G) demonstrates an L.Y. of 2,300 ± 500 ph/MeV under x-ray excitation (Fig. 7H). Furthermore, Sb³⁺-based OIHPs exhibit responsiveness to higher-energy γ-rays: Gua₃SbCl₆ achieves an L.Y. of 1,800 ± 500 ph/MeV under 120-keV ⁶⁰Co γ-ray irradiation (Fig. 7I) [121].

A₃BiX₆-type MHPs

As another P-block cation, Bi³⁺ is also a promising B-site constituent for constructing A₃BiX₆ MHPs [122]. The greater atomic mass of Bi³⁺ relative to Sb³⁺ reduces lattice vibrational frequencies, thereby enhancing carrier mobility and improving the suitability of A₃BiX₆ for photodetector applications [123,124]. The intrinsic luminescence of Cs₃BiCl₆ single crystal at 390 nm arises from the parity-forbidden ³T_1u → ¹A_1g transition of Bi³⁺, while the dual-band absorption at 220 and 330 nm originates from the ¹A_1g → ¹T_1u and ¹A_1g → ³T_1u transitions, respectively [125]. Similarly, Cs₃BiBr₆ NCs display blue emission at RT with a PLQY of merely 6.03%, which could increase to 22% upon oleic acid passivation [126]. The poor luminescence efficiency of Cs₃BiX₆ due to strong exciton–phonon coupling and severe nonradiative recombination has shifted research focus toward its potential for UV dual-band photodetection.

The fabricated photodetectors based on Cs₃BiBr₆ single crystals show an impressive detectivity of 8 × 10⁸ Jones and a low dark current under 400-nm illumination (Fig. 8A and B) [123]. Given that Cs₃BiBr₆ and Cs₃Bi₂Br₉ are interconvertible, Cs₃BiBr₆ can undergo phase transformation to form Cs₃Bi₂Br₉ during synthesis using identical precursors [18,122]. Fang’s group [127] successfully constructed a Cs₃BiBr₆/Cs₃Bi₂Br₉ bulk heterojunction applying with dual-band photodetection (Fig. 8C). In this regard, the self-powered ITO (ITO = indium tin oxide)/Cs₃BiBr₆/Cs₃Bi₂Br₉/Au photodetector achieves responsivities of 59.4 mA/W at 360 nm and 3.09 mA/W at 450 nm (Fig. 8D) [124].

To overcome the limitation of inherent challenges in photodetectors, such as narrow optical absorption range and low carrier mobility, the favorable band alignment between Cs₃BiCl₆ and GaN enables the formation of a built-in electric field at their heterojunction interface [128]. The interfacial electric field suppresses carrier recombination and separates photogenerated electron–hole pairs, significantly enhancing responsivity and detection sensitivity. The Cs₃BiCl₆/GaN heterojunction photodetector achieves exceptional performance: strong specific detectivity (1.23 × 10¹² Jones) and ultrafast response (τ_r/τ_f = 28/190 μs). Its intrinsic UV dual-band selectivity enables applications in logic operations and encrypted optical communication systems (Fig. 8E).

On the one hand, the A₃BiX₆ MHPs show strong application into photodetection. On the other hand, the absence of PL in A₃BiCl₆ (A = Rb and Cs) at RT is attributed to the strong exciton–phonon coupling with the coupling constant reaching 693 meV, which facilitates severe nonradiative recombination [33], structural and vibrational studies indicate that the RT luminescence quenching of A₃BiX₆ is closely related to pronounced local distortion of isolated [BiX₆]³⁻ octahedra and strong lattice anharmonicity [129]. To enhance the efficiency of radiative recombination, ns²-typed Sb³⁺ was incorporated into Rb₃BiCl₆ (i.e., Rb₃BiCl₆:Sb³⁺), resulting in a bright STE emission with a reduced coupling constant of 347 meV (Fig. 8F), the PLQY increased to 33% [33]. The strategy of structural modifications further improved the PLQY, achieving a maximum of 45% in Rb₂CsBiCl₆:Sb³⁺ (Table 7) [130–132]. Beyond ns²-type dopants, transition-metal cation Mn²⁺ is also regarded as effective dopant. Due to the primarily participation of Mn d orbitals in the conduction band minimum (CBM), both (Cs₂K)BiCl₆:Mn²⁺ and Cs₃BiCl₆:Mn²⁺ can exhibit a narrow bandgap and an allowed ⁴T₁ → ⁶A₁ transition [18,133]. Direct Mn²⁺ doping yields weak NIR emission, while Sb³⁺, Cr³⁺ codoping enables efficient ET (PLQY = 11.03%). Sb³⁺-induced quasi-2D domains further enhance PLQY to 30.68%, enabling multifunctional NIR LEDs for night vision, penetration imaging, and vein visualization [134].

Although Cs₃BiCl₆ exhibits negligible emission at RT, its PL intensity significantly increases when the temperature falls below 80 K, as shown in Fig. 8G [122,125]. This behavior suggests that radiative recombination becomes more favorable at low temperatures under UV excitation, due to the suppression of thermally activated nonradiative processes. Under high-energy radiation excitation, a large number of high-energy electron–hole pairs are generated, creating dense excitation conditions that allow radiative recombination pathways to effectively compete with nonradiative processes. As a result, Cs₃BiCl₆ exhibits dual emission bands at 400 and 600 to 700 nm under x-ray excitation, accompanied by fast decay kinetics (τ₁ = 0.61 ns [43%] and τ₂ = 9.4 ns [57%]) (Fig. 8H and I). Notably, an L.Y. of approximately 800 ph/MeV has been achieved under ¹³⁷Cs γ-ray irradiation (Fig. 8J), highlighting the potential of Cs₃BiCl₆ for radiation detection applications [125].

A₃REX₆-type MHPs with empty f orbitals

As for the A₃REX₆ MHPs, RE³⁺ with empty f orbitals (since La³⁺ has empty f orbitals and Sc³⁺ and Y³⁺ lack f orbitals, these ions are collectively treated as RE³⁺ with empty f orbitals in this work) is similar to the P-block cation as B-site composition, including the intrinsic luminescence mechanism and water-driven phase transition. The intrinsic luminescence for Cs₃ScCl₆, Cs₃YCl₆, and Cs₃LaCl₆ single crystals is ascribed to STE emission [72,135,136], albeit with relatively low efficiencies, as in the case of Cs₃YCl₆, the PLQY is merely 3.1% [72]. Relatively, their NCs could achieve better PL properties due to the surface modifications by oleic acid ligands [137,138]. Based on this strategy, the PLQY of Cs₃YCl₆ NCs achieves up to 89.3%, while its single crystal is still limited to the modest PLQY (<10%) [139]. The water-driven strategy is also effective for incorporating H₂O into the lattice, converting A₃REX₆ into A₂REX₅·H₂O. The phase-transformed Cs₃ScX₆ and Cs₂ScCl₅·H₂O demonstrate excitation wavelength-dependent luminescence at RT (Fig. 9A). The femtosecond transient absorption, temperature-dependent PL, and time-resolved PL studies reveal that this tunable emission originates from 2 distinct STE states. Selective excitation to different STE states through wavelength modulation enables emission color tuning from cyan through white to yellow [140].

Although Cs₂ScCl₅·H₂O exhibits excitation wavelength-dependent PL with low efficiency, using Sb³⁺ as a ns²-typed dopant enables direct ET to yellow-emitting STE states, boosting the PLQY to nearly 100% [140]. Similarly, Sb³⁺ doping in Cs₃ScCl₆ also enhances the luminescence efficiency. A comparative study of Sb³⁺-doped A₃REX₆ MHPs revealed that structural evolution results in tunable emission (Table 8): Cs₃ScCl₆:Sb³⁺ emits cyan (500 nm) [141], Cs₃YCl₆:Sb³⁺ emits green (545 to 550 nm) [72,142], and Cs₃LaCl₆:Sb³⁺ emits yellow (570 nm) [142]. This PL tunability may originate from the local distortion of the [SbCl₆]³⁻ octahedral in the host lattices (Fig. 9B), which alters the Sb–Cl bond lengths and consequently modulates the energy levels of the frontier molecular orbitals. Intriguingly, Cs₃ScCl₆:Sb³⁺ NCs exhibit white emission under 365-nm excitation (Fig. 9C), attributed to the partial transformation into carbon dots during synthesis. The resulting synergy between broad STE emission and blue emission from carbon dots enables full-spectrum coverage, i.e., white light [143]. Similarly, the white LED based on Cs₃ScCl₆:Sb³⁺ maintains stable white emission under 200 mA, achieving a high CRI (=90) and a luminous efficacy of 23 lm/W (Fig. 9D) [143]. Likewise, the white LED fabricated from Cs₃LaCl₆:Sb³⁺ reaches a CRI of 91 at 25 mA, with brightness further increased at higher currents (Fig. 9E) [142]. Ln³⁺ incorporation enables efficient STE–Ln³⁺ ET for NIR emission; Br^– substitution renders the ET efficiency of Cs₃La_0.5Nd_0.5Br₆ nearly unity and boosts the PLQY of Cs₃La_0.17Nd_0.83Br₆ NCs to 64.65% (after APTN treatment), enabling NIR LEDs with 3.49% EQE and a 488-min T₅₀ lifetime [144].

Furthermore, Rb₂ScCl₅·H₂O:Sb³⁺ exhibits x-ray absorption coefficients comparable to CsI and α-Se, with a radiation sensitivity of 58.5 μC·Gy⁻¹·cm⁻² (2.9 times higher than commercial α-Se) (Fig. 9F) [145]. Cs₃YCl₆:Sb³⁺ exhibits identical STE emission under x-ray (6.6 mGy/s) as UV excitation, achieving an L.Y. of 16,000 ph/MeV. At an SNR of 3, its detection limit reaches 1.12 μGy/s, far below medical diagnostic thresholds (Fig. 9G). Flexible films of Cs₃YCl₆:Sb³⁺ embedded in polydimethylsiloxane (PDMS) enable high-resolution x-ray imaging, resolving internal structures of adapters, earphones, and circuit boards at dose rate of 1.2 mGy/s, with a spatial resolution up to 9 lp/mm (Fig. 9H) [72].

Compared to ns²-typed dopants, Ln³⁺ as dopant shows better compatibility with A₃REX₆ MHPs for enhancing PL and RL performance. Replacing Y³⁺ with La³⁺ enlarges the [LnCl₆]³⁻ polyhedra, increasing electron density and inducing greater lattice distortion [142]. This effect is observed in both Ln³⁺ with empty f orbital and Ln³⁺ with f orbital, such as Gd³⁺ and Lu³⁺ [142]. The distortion caused by different Ln³⁺ alters the electronic structure of A₃REX₆, directly impacting its luminescent properties [142,143].

When Ce³⁺ is incorporated as a luminescent center in A₃REX₆ host such as Cs₃ScCl₆, Li₃YCl₆, and Cs₃LaX₆ (X = Cl, Br, and I), dual-shoulder characteristics are observed in the emission peaks of PL and RL spectra within low doping levels, accompanied by rapid decay times (Fig. 10A and B) [58,135,146]. In addition, Cs₃LaCl₆:Ce³⁺ and Cs₃LaBr₆:Ce³⁺ exhibit remarkable thermal quenching resistance, with PL and RL intensities decreasing by less than 25% from 40 to 500 K (Fig. 10C and D). This stability arises from enhanced ET from host-derived STEs to Ce³⁺ ions at elevated temperatures (Fig. 10E) [136]. A similar ET is observed in Cs₃ScCl₆:Ce³⁺ [135], underscoring the critical role of STE-to-activator energy migration in thermal stability.

Notably, Ce³⁺-doped A₃REX₆ MHPs primarily focus on high-energy scintillation. For instance, Cs₃ScCl₆ achieves optimal scintillation properties at 0.5% Ce³⁺ doping, delivering an L.Y. of 9,200 ph/MeV under 662-keV ¹³⁷Cs γ-ray excitation (Fig. 10F) [135]. Similarly, Li₃YCl₆ with 1% Ce³⁺ exhibits an L.Y. of 6,185 ph/MeV under identical conditions [146]. High L.Y. and reduced E.R. are observed in Cs₃LaCl₆ and Cs₃LaBr₆ synthesized via the multiple alternating direction melt-mixing and cooling method at elevated doping concentrations. For example, Cs₃LaCl₆:10% Ce³⁺ achieves an L.Y. of 20,000 ph/MeV under 662-keV ¹³⁷Cs γ-ray excitation, with an E.R. of 9% at 40% Ce³⁺. Cs₃LaBr₆:10% Ce³⁺ demonstrates even higher performance, reaching 35,000 ph/MeV and 8% E.R. at 40% Ce³⁺ doping [34]. However, crystal quality significantly impacts scintillation metrics. Bridgman-grown Cs₃LaCl₆:8% Ce³⁺ and Cs₃LaBr₆:15% Ce³⁺ show reduced L.Y. (16,000 and 32,500 ph/MeV, respectively) but improved E.R. (8.6% and 4.9%, respectively) (Fig. 10G and H). Remarkably, Bridgman-synthesized Cs₃LaI₆:0.5% Ce³⁺ achieves an exceptional L.Y. of 43,000 ph/MeV (Fig. 10I) [58].

A₃LnX₆ MHPs with f orbitals based on light Ln³⁺

Light lanthanides (Ln³⁺ = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, and Eu³⁺) with f orbitals, when incorporated B-site luminescent center ions of A₃LnX₆ MHPs, exhibit fundamentally different luminescence and scintillation properties relative to A₃REX₆ MHPs lacking f orbitals. This difference originates from the unfilled 4fⁿ electron configuration of Ln³⁺ ions, which gives rise to characteristic 4f–4f or 5d–4f transitions. In particular, Eu³⁺ and Ce³⁺ serve as representative Ln³⁺ emitters (Table 9), whose bright luminescence stems from the strong shielding of the 4f orbitals by the outer 5s²5p⁶ orbitals.

As Eu³⁺ is incorporated as B-site host composition, it tends to undergo partial reduction to Eu²⁺, resulting in the coexistence of both dual oxidation states within distinct luminescence characteristics. Specifically, Eu³⁺ contributes red emission via f–f transitions, while Eu²⁺ emits blue light through the 4f⁷ → 4f⁶5d¹ transition. Exploiting this duality, Cs₃EuCl₆ NCs exhibit excitation-wavelength-dependent multicolor emission, ranging from red to deep blue [147]. A similar photochromic effect is also observed in Cs₃TbCl₆ (Fig. 11A); both Cs₃EuCl₆ and Cs₃TbCl₆ NCs have been utilized in anticounterfeiting inks, enabling dynamic and multicolor pattern encoding (Fig. 11B) [147]. To further enhance PL properties of Cs₃EuCl₆, constructing ET channels using organic ligands represents another effective strategy [148,149]. For instance, the small molecule ethyl 7-hydroxycoumarin-3-carboxylate (EHC) coordinates with undercoordinated Ln³⁺ through its carbonyl group, passivating surface defects. Furthermore, its singlet excited state exhibits strong spectral overlap with Ln³⁺’s absorption, significantly boosting the overall ET efficiency [150]. Based on this strategy, EHC-passivated Cs₃EuCl₆ achieves PLQY of 92.4%. The LED devices based on EHC-Cs₃EuCl₆ achieved an EQE of 5.17% and an L_max of 370 cd/m² (Fig. 11C and D). Notably, the red LED based on EHC-Cs₃EuCl₆ NCs achieved a T₅₀ of 440 h at an initial luminance of 100 cd/m² [150], outperforming most reported MHP-based LEDs. However, the T₅₀ of the EHC-Cs₃EuCl₆ LED remains inferior to commercial LEDs due to defect accumulation, halide migration, interfacial degradation, and thermally activated instability under continuous operation.

The emission of A₃CeX₆ also originates from the parity-allowed 5d–4f transition, resulting in a fully permitted emission in the UV or blue spectral regions with nanosecond-scaled lifetime [73]. According to the CsBr–CeBr₃ phase diagram in Fig. 11E, the stable phases are limited to Cs₃CeBr₆ and CsCe₂Br₇ [73]. As for the PL application, Cs₃CeBr₆ featuring a single Ce³⁺ emissive center, good stability, and few defects compared with CsCe₂Br₇ with the dual Ce³⁺ emissive centers (Fig. 11F) [151] exhibits a high PLQY of ~90% and a fast decay time of ~28 ns. Tang et al. fabricated an LED device with Cs₃CeBr₆ as the active layer via a dual-source coevaporation method, achieving an L_max of 25 cd/m² and an EQE of 0.46% (Fig. 11G), and obtained a white LED by combining it with a yellow Y₃Al₅O₁₂:Ce phosphor down-converter (Fig. 11H) [73]. Compared to Cs₃CeBr₆, Cs₃CeI₆ enables spectral tuning by shifting the emission from the UV to deep-blue region (Fig. 12A), which can result in a narrower spectral emission and enhanced color purity in LEDs [13,14]. Density functional theory (DFT) calculations further reveal that Cs₃CeI₆ possesses a higher exciton binding energy (225 meV) than Cs₃CeBr₆ (135 meV) [73,152]. Furthermore, the film fabrication process was optimized; the high-quality, dense, and uniform Cs₃CeI₆ thin films were fabricated using a 5-nm CsCl seed layer and dual-source coevaporation; and the resulting deep-blue LED device (ITO/ZnO/Al₂O₃/Cs₃CeI₆/MCP/TAPC/HAT-CN/Al) achieved an L_max of 470 cd/m² and an EQE_max of 3.5% (Fig. 12B and C) [13]. The luminescence mechanism of Cs₃CeI₆ is driven by ET from STEs of I₂⁻ species to Ce³⁺-based Frenkel excitons (CFEs) (Fig. 12D), and increasing STE-CFE spectral overlap with excess CsI could improve ET process, resulting in a deep-blue LED with high L_max of 1,075 cd/m² and an EQE_max of 7.9% (Fig. 12E and F) [14].

The narrowband absorption of Cs₃CeBr₆ enables solar-blind UV detection without requiring additional optical filters, making it highly suitable for UV photodetector applications [15]. In general, Cs₃CeBr₆ films prepared by spin-coating, suffer from high trap-state densities and relatively low carrier mobility, limiting their utility in UV photodetectors. Seok et al. through a postannealing optimization process reduced the trap state density in Cs₃CeBr₆ films to approximately 8 × 10¹² cm⁻²·eV⁻¹ while simultaneously increasing the field-effect carrier mobility to about 10 cm²·V⁻¹·s⁻¹. The UV photodetectors fabricated from the optimized films demonstrated a high responsivity of 2.05 A/W, a detectivity of 1.48 × 10¹³ Jones (Fig. 13A), and a wide linear dynamic range of 99.64 dB (Fig. 13B). The optimized Cs₃CeBr₆ films as the UV photodetector also exhibited fast response times (rise time, 93 ms; fall time, 345 ms), excellent spectral selectivity, and remarkable stability, retaining ~91% of their initial photocurrent even after 60 d of storage without encapsulation [15]. Similar to Cs₃CeBr₆, Cs₃CeCl₆ features effectively UV absorption and convert it into electrical signals, making its potential for UV photodetectors. While Cl⁻ substitution of Br⁻ improves intrinsic thermal stability, the strong polarity of the Ce–Cl bond renders the material prone to oxidation and hydrolysis reactions [153,154]. To address this, Gd³⁺ is introduced into the crystal lattice of Cs₃CeCl₆. On the one hand, the incorporation of Gd³⁺ enhances material stability and improves film compactness, thereby boosting charge transport efficiency. On the other hand, the partial substitution of Ce³⁺ sites by Gd³⁺ increases the interionic distance between Ce³⁺, suppressing concentration quenching effects, reducing radiative reabsorption, and elevating the PLQY to 96%, which enhances detector sensitivity. Ultimately, the UV photodetector fabricated based on Gd-doped Cs₃CeCl₆:Gd³⁺ thin films demonstrates high detectivity (7.938 × 10¹¹ Jones), high responsivity (0.195 A/W) and the dark current densities at 0- and −0.1-V bias voltages are as low as 4.4 × 10⁻¹⁰ and 1.9 × 10⁻⁷ A/cm², respectively (Fig. 13C and D) [155].

Owing to the excellent x-ray response of Ce³⁺ and Eu³⁺, A₃CeX₆ and A₃EuX₆ have been explored for x-ray imaging applications [156]. The Cs₃CeCl₆ film achieved a spatial resolution of 11 lp/mm [157], while the Cs₃EuCl₆@PDMS composite film realized a spatial resolution of 9 lp/mm [158]. In addition, (MTP)₃EuCl₆ (MTP = methyl(triphenyl)-phosphonium) glass exhibited a spatial resolution of 14.3 lp/mm together with recoverable radiation stability (Fig. 13E) [159].

Beyond its applications in photodetectors, electroluminescent LEDs, and x-ray imaging, the utility of A₃CeX₆ extends to γ-ray scintillation. Under ¹³⁷Cs γ-ray irradiation, Cs₃CeCl₆ demonstrates an L.Y. of 19,000 ph/MeV and an E.R. of 8.4% [17]. Slow cooling to reduce light-scattering defect concentrations enabled the growth of a large single crystal (Φ10 mm × 30 mm, Fig. 13F), thereby enhancing the L.Y. to 21,000 ph/MeV and lowering the E.R. to 7.6% (Fig. 13G) [160]. However, challenges such as internal stress, insufficient release of crystallization latent heat, and by-product formation persist in the Bridgman method. In contrast, mechanical grinding emerges as an eco-friendly alternative, enhancing luminescent performance and thermal stability while minimizing by-products and chemical waste. Mechanically ground Cs₃CeCl₆, Cs₃TbCl₆, and Cs₃EuCl₆ powders exhibit x-ray-induced quantum tunneling effects, where high-energy ionizing radiation facilitates electron tunneling between trap states and the conduction band [161]. The hydrated phase Cs₃CeCl₆·3H₂O was also synthesized, which preserves the excellent scintillation performance of Cs₃CeCl₆ while benefiting enhanced properties due to water incorporation. Under x-ray irradiation, it achieves a high L.Y. of 31,900 ph/MeV, surpassing commercial LuAG:Ce. It exhibits a LoD as low as 108 nGy/s and a spatial resolution of 12 lp/mm, making it suitable for high-resolution imaging applications [162]. As similar as nanosecond-scaled decay time with Cs₃CeCl₆, Cs₃PrCl₆ exhibits the 4f¹5d¹ → 4f² transition with fast scintillating decay time (11.7 ns [53%] and 72 ns [47%]) (Fig. 13H) and L.Y. of 5,900 ph/MeV under ¹³⁷Cs γ-ray excitation (Fig. 13I) [163]. As expected, Cs₃CeCl₆ and Cs₃PrCl₆ are promising scintillators as radiation detectors in time-of-flight positron emission tomography.

A₃LnX₆ MHPs with f orbitals based on heavy Ln³⁺

Although some medium-heavy Ln³⁺ possess electrons in their f orbitals, A₃LnX₆ MHPs still exhibit both intrinsic luminescence and characteristic f–f or d–f transition. In general, Gd³⁺, Tm³⁺, and Yb³⁺ are utilized as B-site host composition, the PLQY of Cs₃GdCl₆ NCs, Cs₃TmCl₆ NCs, and Cs₃YbCl₆ NCs after oleic acid passivation is 30.3%, 22.8%, and 59.8%, respectively, attributed to intrinsic STE emission [27,139]. Herein, the white LED based on Cs₃TmCl₆ shows a CRI of 87.0, a CCT of 5,283 K (Fig. 14A), and a T₅₀ of 336 h (Fig. 14B), surpassing the T₅₀ reported in prior studies [27].

In A₃LnX₆, the incorporation of ns²-typed Sb³⁺ dopant induces local Jahn–Teller distortions owing to the low-symmetry coordination environment, thereby enhancing STE emission [164]. The extent of distortion depends on the specific B-site host composition. For example, Cs₃GdCl₆:Sb³⁺, Cs₃YbCl₆:Sb³⁺, and Cs₃LuCl₆:Sb³⁺ emits at ~545 nm [22,142], 533 nm [165], and 525 nm [166], respectively, and their PLQY could increase to 96.3%, 66.9%, and 99% (Table 10) [22,165,166]. The white LED based on Cs₃GdCl₆:Sb³⁺ exhibits a high CRI of 96.5 (Fig. 14C). Furthermore, excellent thermal quenching resistance enable the long-term operation of white LED (Fig. 14D) [22]. Meanwhile, the white LED based on Cs₃LuCl₆:Sb³⁺ exhibits excellent color quality, with a high CRI of 94 and a CCT of 5,565 K, and also shows strong resistance to thermal quenching [166]. Interestingly, Cs₃YbCl₆:Sb³⁺ allowed a reversible transformation to Cs₂YbCl₅·H₂O:Sb³⁺, which is analogous to transformation from Cs₃InCl₆:Sb³⁺ to Cs₂InCl₅·H₂O:Sb³⁺ [87,165]. The water-driven strategy would be triggered rapidly after exposure to methanol (within 15 s), accompanying with an emission color change from yellow to green (Fig. 14E) [165]. This stimulus-responsive luminescence switching reveals the potential of information encryption as the former turns green, while the latter remains yellow [165]. Moreover, Cs₃LuCl₆:Sb³⁺ delivers 7,300 ph/MeV and a LoD of 0.4 μGy/s, with flexible films achieving a spatial resolution of 11.5 lp/mm [167]. A Cs₂NaLuCl₆:Sb³⁺/Cs₃LuCl₆:Sb³⁺ heterojunction enhances RL to 2.4× BGO and lowers the detection limit to 140 nGy/s and a spatial resolution of 14 lp/mm, while Mn²⁺ incorporation enables trichromatic emission for color x-ray imaging [69]

Beyond the intrinsic luminescence, Ln³⁺ as B-site host and dopant enables the tunable emission with ET process, based on the characteristic f–f or d–f transitions (Fig. 15A) [19,168,169]. Under x-ray excitation, 0.5-in Cs₃GdCl₆:Ce³⁺ and Cs₃GdBr₆:Ce³⁺ exhibit the L.Y. of 40,000 and 48,000 ph/MeV, respectively (Fig. 14F). When excited by ¹³⁷Cs γ-ray, their L.Y. reaches 24,500 and 47,000 ph/MeV, with E.R. of 4.5% and 4.0%, respectively (Fig. 14G and H). Relatively, Cs₃GdBr₆:Ce³⁺ delivers the highest L.Y. and lowest E.R. reported among A₃BX₆ MHPs under ¹³⁷Cs γ-ray excitation [32]. Cs₃TbCl₆:Sb³⁺ NCs achieved an L.Y. of 20,300 ph/MeV, a reduced detection limit of 212 nGy/s (Fig. 15B), and an improved spatial resolution of 9.6 lp/mm (Fig. 15C). They further enabled high-contrast imaging of circuit features across a wide range of irradiation doses [16].

Although ET process toward Ln³⁺ to Ln³⁺ is environmentally insensitive, it mainly involves quadrupole–quadrupole [170], Cs₃Tb_0.5Ce_0.5Cl₆ establishes an efficient ET pathway of Ce³⁺ → Tb³⁺ channel (Fig. 15D), suppressing nonradiative recombination and achieving a PLQY of up to 86%. The white LED based on Cs₃Tb_0.5Ce_0.5Cl₆ exhibited a CRI of ~78 and a light efficiency of ~118 lm/W at 25 mA (Fig. 15E) [171]. In addition to Ce³⁺-sensitized dopant, A₃TbF₆:Eu³⁺ (A = Cs and Rb) demonstrates stimulus-responsive luminescence based on humidity-induced phase transitions. Initially, weak orbital coupling between Eu³⁺ and Tb³⁺ results in low ET efficiency, with dominant green emission from Tb³⁺. Upon exposure to a humid environment, the material undergoes a phase transition to A₂TbF₅:Eu³⁺, where shortening interionic distance and triggering efficient energy coupling between Tb³⁺ and Eu³⁺ activate the ET process and characteristic Eu³⁺ red emission (Fig. 15F) [168,169]. Screen-printed patterns utilizing differently doped Cs₃TbF₆ crystals have been developed for information encryption, where concealed multicolor graphics become visible only under specific stimulus conditions (Fig. 15G) [169]. Furthermore, beyond their kinetically tunable hydrochromic luminescence properties, Rb₃TbF₆:Eu³⁺ crystals also exhibit excitation-wavelength-dependent luminescence phenomena, attributed to the unique light absorption of Eu³⁺ at 393 nm. Leveraging this phenomenon, 4 distinct sample sets can generate varying arrays of color combinations depending on the excitation/stimulus conditions. These combinations can serve as identification codes for encryption (Fig. 15H) [168].

As one of the high-efficiency scintillator, A₃TbCl₆ (A = Cs and Rb) exhibits similar excited-state relaxation pathways under both low- and high-energy excitations [161]. The scintillation properties of A₃TbCl₆ are dependent on its structural form (e.g., polycrystalline, microcrystalline, or glass), which, in turn, is dictated by the synthesis route. The performance divergence between polycrystal and microcrystal forms is largely dictated by variations in grain size, orientation, grain boundary density, and film compactness. Benefiting from large grain sizes, Cs₃TbCl₆ and Rb₃TbCl₆ polycrystals achieve impressive L.Y. of 56,800 and 88,800 ph/MeV, respectively, with LoD of 149.65 and 115.38 nGy/s (Fig. 16A) under x-ray excitation. The spatial resolution of Cs₃TbCl₆ and Rb₃TbCl₆ polycrystals films reach 3.3 and 3.9 lp/mm, respectively (Fig. 16B) [31]. Although the reduced grain size of RT recrystallized Cs₃TbCl₆ microcrystals led to a lower L.Y. of 51,800 ph/MeV, this refinement in microstructure enabled the fabrication of a denser, more uniform film. This resulted in a significantly improved spatial resolution of 12 lp/mm and a lower LoD of 63 nGy/s (Fig. 16C and D) [83]. In addition, the glass scintillator prepared by substituting Cs⁺ with organic groups (e.g., Bzmim⁺), although resulting in a decrease in L.Y., the high transmittance of the glass has achieved a high spatial resolution of 25 lp/mm (Fig. 16E and F) [172]. In general, polycrystals typically achieve high L.Y.s owing to their large grain size; microcrystals facilitate the fabrication of dense films, leading to a low detection limit; and highly transparent glasses offer high spatial resolution. Introducing emissive fluorophores to construct ET channels with Ln³⁺ enhances radiative performance, as exemplified by (BuTPP)₃TbCl₆ (BuTPP = butyltriphenylphosphonium) glass achieving 8,100 ph/MeV of L.Y., 0.93 μGy/s of LoD, and 26.8 lp/mm of spatial resolution [173].

Machine Learning for A₃BX₆ MHPs with Enhanced Radiative Transitions

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Exploring the broad compositional landscape of A₃BX₆ perovskites remains challenging using conventional approaches, this is mainly reflected in long experimental cycles, high material costs, and limited reproducibility, motivating the introduction of machine learning (ML) as an efficient tool for high-throughput prediction and guided synthesis. Im et al. [174] demonstrated this potential by constructing a 1,703-composition Cs-B-X library and using crystal graph convolutional neural networks to learn structural features, ultimately identifying 40 thermodynamically stable compounds (Fig. 17A). Among them, 27 have been experimentally verified, while several other experimentally confirmed that stable compounds were not captured by the ML predictions.

Such structural stability mapping is particularly relevant for scintillators, as the accessible compositional phase space constrains the formation of thermodynamically stable hosts and helps preselect candidates with favorable electronic and optical properties, such as bandgap width. Building on this foundation, ML can act as a “virtual experimentalist” by learning quantitative correlations between host structures and photophysical properties, enabling the rapid evaluation of thousands of candidate materials prior to synthesis (Fig. 17B) [175].

For scintillators, the fundamental L.Y. can be approximated as the product of 3 constituent processes: absorption, ET, and luminescence Eq. (13) [176]:

L . Y . = E γ β E g ⋅ η 2 ⋅ η 3

(13)

where E_g is the bandgap of scintillators, E_γ is the energy of the incident radiation, and η₂ and η₃ are the efficiencies of ET and intracenter luminescence, respectively. Herein, the E_g can be efficiently computed from electronic structure calculations, serving as a physically meaningful descriptor for ML-based prediction of L.Y. (Fig. 17C).

Beyond E_g, the overall L.Y. also depends on the carrier recombination efficiency, which is governed by the interplay between the thermalization length and the Onsager radius (R_Ons). R_Ons represents the distance at which the Coulomb potential between an electron and hole equals the thermal energy and can be expressed as Eq. (14) [177]:

R Ons = e 2 4 πε 0 ε r k B T

(14)

where e is the elementary charge, k_B is the Boltzmann constant, ε₀ is the permittivity of free space, T is the absolute temperature, and ε_r is the relative dielectric constant of the host (including both ionic and electronic contributions). Thermalized carriers separated by a distance r recombine with probability 1 − exp(−R_Ons/r) or escape with probability exp(−R_Ons/r). Therefore, R_Ons and ε_r directly influence electron–hole recombination and serve as key descriptors for ML prediction of L.Y. at RT.

Together, Pilania et al. [176] investigated a set of 25 Eu²⁺- and Ce³⁺-doped scintillators by computing bandgaps, densities, and both ionic and electronic contributions to the dielectric constant using DFT. ML models based on Kernel Ridge Regression and AdaBoost were then trained to predict L.Y. and scintillation performance. Their results show that both a smaller E_g and a lower ionic contribution to ε_r tend to achieve higher L.Y. (Fig. 17D and E) [176].

Although ML methods have shown great potential in predicting the properties of perovskite materials, their practical application still faces several limitations. On the one hand, compared with datasets in bioinformatics or genomic prediction that often contain tens of thousands of entries, the datasets currently available for perovskite structure and property prediction remain relatively small, and the descriptors used to characterize luminescence performance are still limited. On the other hand, light emission is fundamentally governed by excited-state carrier dynamics and electron–phonon coupling, which cannot be fully captured by ground-state DFT descriptors. Consequently, predicting luminescence properties solely based on ground-state DFT parameters has intrinsic limitations. Notably, recent studies have shown that methods such as time-dependent DFT, GW–Bethe–Salpeter equation method, and surface hopping can more effectively describe the excited-state properties of materials [178–180].

Conclusion and Prospects

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A₃BX₆ MHPs feature tunable electronic structures, highly tolerant crystal lattices, and functional charge carriers generated under optical or electrical excitation, which endow them with broad application prospects in optoelectronic and scintillation applications. This review summarizes recent progress in A₃BX₆ MHPs (A₃SbX₆, A₃InX₆, A₃BiX₆, A₃REX₆, and A₃LnX₆) with a focus on B-site dopant engineering and its influence on radiative transition mechanisms. B-site cation engineering effectively modulates the electronic structures and luminescence pathways in these materials. Specifically, ns²-typed dopant induce STE emission, while transition-metal and RE dopants activate characteristic d–d, d–f, and f–f transitions, enabling tunable PL and EL. In addition to conventional light emission applications, A₃BX₆ MHPs also exhibit excellent performance in x-ray and γ-ray detection, owing to their strong high-energy photon absorption, low self-absorption, and broad spectral response.

Despite their tunable luminescence and enhanced scintillation performance, the practical development of A₃BX₆ MHPs continues to face substantial challenges and opportunities, including but not limited to the following:

1.	The high CRI of A₃BX₆ MHPs is advantageous for white-light LED applications; however, the inherently broad emission spectra limit the achievable color purity for narrowband or monochromatic LEDs. In addition, the relatively low PLQY in the NIR spectral region may constrain their performance in bioimaging, NIR sensing, and other NIR photonic applications.
2.	Although the EQE of deep-blue A₃BX₆ LEDs reaches 7.9%, which is relatively high for this challenging spectral region, the EQE of green and red LEDs remains below the reported records, indicating that further optimization of charge carrier injection, recombination efficiency, and material stability is required.
3.	In the field of x-ray scintillators, RE A₃BX₆ MHPs are promising candidates for high-resolution x-ray imaging due to their high L.Y. (maximum L.Y. = 88,800 ph/MeV), low detection limit (minimum LoD = 63 nGy/s), and high spatial resolution (highest spatial frequency = 18.5 lp/mm). However, current studies predominantly report NCs or submillimeter-sized single crystals, which critically influences edge emission, photon escape, suboptimal light coupling, and reduced optical transmittance, thereby limiting the overall scintillation performance. To address this, further advances in crystal growth techniques and scalable strategies for producing centimeter-scale single crystals are essential to obtain the superior scintillation properties.
4.	In the field of γ-ray scintillators, RE A₃BX₆ MHPs have demonstrated considerable promise owing to their high L.Y. (maximum L.Y. = 47,000 ph/MeV) and low E.R. (minimum E.R. = 4.0%). However, these values remain inferior to those of state-of-the-art scintillators such as LaBr₃:Ce, which exhibits an L.Y. of 74,196 ph/MeV and an E.R. of ~3% at 662 keV [181]. In general, the high scintillation performance of A₃BX₆ MHPs has been mainly achieved by Ce³⁺ doping. However, the characteristic energy levels of Ce³⁺ limit further optimization of L.Y. and decay-time, hindering time-critical applications such as time-of-flight position emission tomography. Future studies should explore multicomponent doping or codoping strategies to require fast response and high photon output.
5.	Compared to CsPbX₃ perovskites, A₃BX₆ MHPs are intrinsically lead-free and exhibit good thermal and radiation stability due to their vacancy-ordered framework and strong B–X bonding. However, environmental factors may still affect their long-term performance. Under high-humidity conditions, certain compositions may undergo hydration-induced phase transitions, which introduce structural defects and degrade luminescence performance. To enhance moisture resistance, strategies such as encapsulation, surface passivation, halide substitution, and lattice rigidification via cation engineering can be used to suppress ion migration and structural rearrangement. Under prolonged irradiation, A₃BX₆ MHPs generally demonstrate high radiation hardness. For example, Rb₃InCl₆:Sb³⁺ exhibits nearly unchanged RL intensity under a cumulative dose of 561.6 Gy, while Cs₂NaLuCl₆/Cs₃LuCl₆:Sb³⁺ maintains stable RL output up to 1,000 Gy. Nevertheless, sustained irradiation may still induce defect accumulation and halide vacancy formation, thereby increasing nonradiative recombination pathways. Further improvement in radiation tolerance requires minimizing initial defect densities, enhancing crystal quality, and strengthening structural stability through cation engineering.

Overall, the above strategies demonstrate that B-site cation engineering is central to achieving enhanced luminescence and scintillation in A₃BX₆ MHPs, providing a foundation for further optimization of synthesis methods, dopant–host compatibility, and interface modification. The incorporation of ns², transition-metal, and RE dopants enables diverse radiative pathways, supporting applications ranging from PL and EL to high-energy radiation detection. Despite the substantial progress achieved, challenges remain in large-scale single-crystal growth, long-term stability, and standardized device evaluation. Future advances may be accelerated by artificial-intelligence-assisted materials discovery, improved crystal engineering, and deeper understanding of carrier dynamics, paving the way for the practical implementation of A₃BX₆ MHPs in next-generation optoelectronic and radiation detection technologies.

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doi: 10.34133/research.1281

Receive Date：2026-01-20
Online Date：2026-10-16
Published：2026-05-20

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Received：2026-01-20
Revised：2026-04-14
Accepted：2026-04-14

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¹College of Materials and Chemistry, China Jiliang University, Hangzhou 310018, China.

²Chemical Physics and NanoLund, Lund University, Lund 22100, Sweden.

³Nano-Science Center and Department of Chemistry, University of Copenhagen, Copenhagen 2100, Denmark.

⁴Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen 518110, China.

Corresponding:

^* Address correspondence to: yinhang@cjlu.edu.cn (H.Y.);

^* Address correspondence to: junsheng.chen@chem.ku.dk (J.C.);

^* Address correspondence to: qinlaishun@cjlu.edu.cn (L.Q.)

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表12种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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Table 1. The key performance metrics of A₃BX₆ MHPs for photodetectors

Compound	Detectivity (Jones)	Responsivity	Dynamic range (dB)	Rise time	Fall time	Ref.
Cs₃BiBr₆	0.8 × 10⁹	25 mA/W	–	0 ms	60 ms	[123]
Cs₃BiBr₆/Cs₃BiBr₉	8.5 × 10¹⁰ (360 nm)	5.6 mA/W (360 nm)	>36.9 (360 nm)	1.4 μs	2.0 μs	[127]
Cs₃BiBr₆/Cs₃BiBr₉	1.0 × 10⁹ (450 nm)	0.6 mA/W (450 nm)	>34.2 (450 nm)	1.4 μs	2.0 μs	[127]
Cs₃BiCl₆/GaN	1.23 × 10¹²	0.26 A/W	123	28 μs	190 μs	[128]
Cs₃CeBr₆	1.48 × 10¹³	2.05 A/W	99.64	93 ms	345 ms	[15]
Cs₃CeCl₆:Gd³⁺	7.938 × 10¹¹	0.195 A/W	–	0.30 s	0.35 s	[155]

MHPs, metal halide perovskites; Ref., reference.

Table 2. The key performance parameters of A₃BX₆ MHPs for LEDs, including EL peak, Commission Internationale de l’Éclairage (CIE) coordinates, EQE, maximum luminance (L_max), and half-lifetime (T₅₀)

Device structure	EL peak (nm)	CIE coordinates	EQE (%)	L_max (cd/m²)	T₅₀	Ref.
Al/TPBi/EHC-Cs₃LaCl₆/PEDO/ITO	442	(0.210, 0.171)	0.53	127	–	[150]
ITO/ZnO/Cs₃La_0.17Nd_0.83Br₆/TCTA/MoO₃/Al	1,070, 1,350	–	3.49	–	488 min	[144]
ITO/PEDOT/PSS/PVK/Cs₃CeBr₆/SPPO13/LiF/Al	392, 430	(0.158, 0.02)	0.44	–	–	[185]
ITO/ZnO/Al₂O₃/Cs₃CeBr₆/TCTA/TAPC/HAT-CN/Al	391, 421	–	0.46	–	–	[73]
ITO/ZnO:PEI/Al₂O₃/Cs₃CeI₆/MCP/TAPC/TAPC:HAT-CN/HAT-CN/Al	430, 470	(0.15, 0.04)	3.5	470	45 min	[13]
ITO/ZnO/Al₂O₃/Rb₃CeI₆/MCP/TAPC/HAT-CN/Al	427, 468	(0.15, 0.06)	0.67	98	–	[186]
ITO/ZnO:PEI/Al₂O₃/Cs₃CeI₆/MCP/TAPC/TAPC:HAT-CN/HAT-CN/Al	435, 480	(0.145, 0.057)	7.9	1,075	72 min	[14]
Al/TPBi/EHC-Cs₃EuCl₆/PEDO/ITO	616	(0.648, 0.338)	5.17	370	440 h	[150]
Al/TPBi/EHC-Cs₃TbCl₆/PEDO/ITO	545	(0.267, 0.418)	1.58	2,373	–	[150]
ITO/ZnO/LiF/Cs₃DyI₆:Er³⁺/TPPO/TCTA/MoO₃/Ag	1,540	(0.25, 0.35)	2.76	–	345 min	[187]

MHPs, metal halide perovskites; LED, light-emitting diode; EQE, external quantum efficiency; EL, electroluminescence.

Table 3. The key performance metrics of A₃BX₆ MHPs for x-ray imaging

Compound	Sample	RL peak (nm)	Tube voltage (kV)	L.Y. (ph/MeV)	LoD (μGy/s)	Film thickness (μm)	f (lp/mm)	MTF	Ref.
Rb₃InCl₆:Sb³⁺	NC	510	30	15,500	5.20 × 10³	200	18.5	0.2	[68]
Cs₃YCl₆:Sb³⁺	Powder	550	70	16,000	1.12	500	9	–	[72]
Cs₃CeCl₆	Film	375, 410	35	7,533	18.3	7.4	10.2	0.2	[157]
Cs₃CeBr₆	Film	390, 425	35	28,510	1.1	7.1	26.4	0.2	[157]
Cs₃EuCl₆	Powder	592, 614	50	12,877	643.1 × 10⁻³	300	9.17	0.2	[158]
Rb₃TbCl₆	Polycrystal	548	80	88,800	115.38 × 10⁻³	260	3.9	0.2	[31]
Cs₃TbCl₆	Polycrystal	548	80	56,800	149.65 × 10⁻³	260	3.3	0.2	[31]
Cs₃TbCl₆:Sb³⁺	NC	548	50	20,300	212 × 10⁻³	–	9.6	0.2	[16]
Cs₃TbCl₆	Powder	547	70	51,800	63 × 10⁻³	1,000	12	–	[83]
Bzmim₃TbCl₆	Glass	547	40	4,101	308.30 × 10⁻³	1,000	25	–	[172]
Bzmim₃EuCl₆	Glass	592, 611	40	1,419	1.56	1,000	–	–	[172]
BuTPP₃TbCl₆	Glass	547	50	8,100	0.93	–	26.8	0.2	[173]
Cs₃LuCl₆/Cs₂NaLuCl₆:Sb³⁺	NC	–	50	–	140 × 10⁻³	200	14	0.2	[69]
Cs₃LuCl₆:Sb³⁺	NC	531	50	7,300	0.4	110	11.5	0.2	[167]
Cs₃LuCl₆:Ce³⁺	Powder	380, 420		8,120	57.9 × 10⁻³	100	8.38	0.2	[188]
Cs₃LuCl₆:Tb³⁺	Powder	548	50	21,000	–	200	11 (423 K)	0.2	[189]
Cs₃LuCl₆:Ce³⁺, Sm³⁺	Powder	604	50	7,600	–	200	8 (423 K)	0.2	[189]

MHPs, metal halide perovskites; NC, nanocrystal; RL, radioluminescence; MTF, modulation transfer function; L.Y., light yield.

Table 4. The key metrics of A₃BX₆ MHPs single crystals (SCs) for γ-ray scintillator

Compound	Crystal size	Density (g/cm³)	γ-Ray source	L.Y. (ph/MeV)	Decay time (ns)	E.R. (%)	Ref.
Cs₃BiCl₆	–	–	¹³⁷Cs	800	0.61, 9.4	–	[125]
Cs₃ScCl₆:0.5% Ce³⁺	Φ ~ 6 × 2 mm	3.32	¹³⁷Cs	9,200	3.6, 54, 963	10	[135]
Li₃YCl₆:Ce³⁺	Φ ~ 4 mm	2.45	¹³⁷Cs	6,185	250, 2,300	–	[146]
Cs₃LaCl₆:20% Ce³⁺	1 × 2 × 2 mm³	3.27	¹³⁷Cs	2,000	56, 380	–	[34]
Cs₃LaCl₆:40% Ce³⁺	1 × 2 × 2 mm³	3.27	¹³⁷Cs	–	54, 314	9	[34]
Cs₃LaBr₆:10% Ce³⁺	1 × 2 × 2 mm³	3.99	¹³⁷Cs	35,000	71, 437	–	[34]
Cs₃LaBr₆:40% Ce³⁺	1 × 2 × 2 mm³	3.99	¹³⁷Cs	–	37, 287	8	[34]
Cs₃LaCl₆:8% Ce³⁺	3 × 3 × 1 mm³	3.36	¹³⁷Cs	16,000	79, 291	8.6	[58]
Cs₃LaBr₆:15% Ce³⁺	3 × 3 × 1 mm³	3.82	¹³⁷Cs	32,500	44, 124	4.9	[58]
Cs₃PrCl₆	3.0 × 3.0 × 1.0 mm	–	¹³⁷Cs	5,900	1.5, 11.7, 72	–	[163]
Cs₃CeCl₆	>1 cm³	3.4	¹³⁷Cs	21,000	50, 300	7.6	[160]
Cs₃CeCl₆	Φ 10 × 30 mm	3.4	¹³⁷Cs	19,000	50, 300	8.4	[17]
Cs₃GdCl₆:Ce³⁺	4–10 mm³	3.56	¹³⁷Cs	24,500	39, 129	4.5	[32]
Cs₃GdBr₆:Ce³⁺	4–10 mm³	4.14	¹³⁷Cs	47,000	72, 270	4	[32]
(Gua)₃SbCl₆	8 × 5 × 3 mm³	–	⁵⁷Co	2,000	2,500	–	[121]

MHPs, metal halide perovskites; L.Y., light yield; E.R., energy resolution.

Table 5. The key performance parameters of commercial scintillators [LYSO = (Lu, Y)₂SiO₅]

Compound	Crystal size	L.Y. (ph/MeV)	E.R. (%)	Decay time (ns)	Proportionality	Afterglow	Hygroscopicity	Radiation Hardness	Ref.
NaI:Tl⁺	Φ150 × 400 mm	38,000	6–7	230	Medium	Noticeable slow component	Hygroscopic	Poor–moderate	[190,191]
LaBr₃:Ce³⁺	89 × 203 mm	61,000	2.7–3.2	16–25	Good	Very low	Highly hygroscopic	Moderate–good	[192,193]
SrI₂:Eu²⁺	1–2 in	90,000	2.6–3.0	1–1.2 × 10³	Excellent	Low	Highly hygroscopic	Moderate	[194,195]
LYSO:Ce³⁺	64 × 220 mm	39,900	8.2	40–42	Moderate	Low	Nonhygroscopic	Excellent	[196,197]

L.Y., light yield; E.R., energy resolution.

Table 6. The key PL properties of A₃InX₆ (including PL peak, FWHM, Stokes shift, decay time and PLQY)

Compound	Sample	PL peak (nm)	FWHM (nm)	Stokes shift (nm)	Decay time	PLQY at λ_ex	Ref.
Cs₃InCl₆	SC	434	88	154	6.85 μs	8% (λ_ex = 280 nm)	[59]
Cs₃InBr₆	NC	450	–	75	8.25 ns	22.3% (λ_ex = 375 nm)	[90]
Cs₃InBr₆	NC	450	–	75	55.59 ns	22.3% (λ_ex = 375 nm)	[90]
Cs₃InCl₆	NC	397	98	107	–	24% (λ_ex = 370 nm)	[71]
Cs₃In(Cl_0.5Br_0.5)₆	NC	424	89	113	–	6% (λ_ex = 370 nm)	[71]
Cs₃InBr₆	NC	440	80	70	–	46% (λ_ex = 370 nm)	[71]
Cs₃In(Br_0.5I_0.5)₆	NC	507	87	103	–	2% (λ_ex = 370 nm)	[71]
Cs₃InI₆	NC	535	87	75	–	16% (λ_ex = 370 nm)	[71]
Rb₃InCl₆:Sb³⁺	SC	497	–	127	288.5 ns	95% (λ_ex = 324 nm)	[87]
Rb₃InCl₆:Sb³⁺	SC	497	–	127	1.82 μs	95% (λ_ex = 324 nm)	[87]
Cs₃InCl₆:Sb³⁺	NC	510	–	170	1.98 μs	93.2% (λ_ex = 340 nm)	[50]
Rb₃InCl₆:Sb³⁺	NC	510	107	230	1.65 μs	68.01% (λ_ex = 320 nm)	[68]
K₃InCl₆:Sb³⁺	SC	505	–	163	4.12 μs (100 K)	–	[97]
					4.46 μs (200 K)
					4.17 μs (400 K)
K₃InCl₆:Sb³⁺	SC	555	–	213	4.69 μs (100 K)	–	[97]
K₃InCl₆:Sb³⁺	SC	555	–	213	4.52 μs (400 K)	–	[97]
Rb₃InCl₆:Sb³⁺	SC	521	112	146	12.5 μs	>90% (λ_ex = 375 nm)	[67]
Cs₃InCl₆:Sb³⁺	NC	512		172	2.07 μs	52.3% (λ_ex = 322 nm)	[21]
Cs₃InCl₆:Cu⁺	SC	398	54	118	13.95 μs	95% (λ_ex = 280 nm)	[59]
Cs₃InCl₆:Sb³⁺/Mn²⁺	NC	530, 620	–	195, 295	1.61 μs	51.38% (λ_ex = 325 nm)	[102]

PL, photoluminescence; SC, single crystal; NC, nanocrystal; PLQY, PL quantum yield; FWHM, full width at half maximum.

Table 7. The key PL properties of A₃BiX₆ (including PL peak, FWHM, Stokes shift, decay time and PLQY)

Compound	Sample	PL peak (nm)	FWHM (nm)	Stokes shift (nm)	Decay time (μs)	PLQY at λ_ex	Ref.
Cs₃BiCl₆	NC	391 (80 K)	60	59	–	–	[122]
Cs₃BiBr₆	NC	435	–	–	2.77 × 10⁻³ (40.19%)	6.03% (λ_ex = 372 nm)	[198]
Cs₃BiBr₆	NC	435	–	–	12.16 × 10⁻³ (26.35%)	6.03% (λ_ex = 372 nm)	[198]
Rb₂CsBiCl₆:Sb³⁺	SC	560	133	182	452 × 10⁻³; 1.29	45% (λ_ex = 378 nm)	[130]
Rb₃BiCl₆:Sb³⁺	SC	625	170	245	4.1	33.6% (λ_ex = 380 nm)	[33]
Cs₃BiCl₆:Sb³⁺	SC	555	132	175	0.54; 1.45	15.85% (λ_ex = 380 nm)	[131]
Cs₃BiCl₆:Sb³⁺	SC	885	250		72.08 (765 nm)	30.68% (λ_ex = 532 nm)	[134]
Cs₃BiCl₆:Sb³⁺	SC	885	250		329.75 × 10⁻³ (885 nm)	30.68% (λ_ex = 532 nm)	[134]
(Cs₂K)BiCl₆:Mn²⁺	SC	605	–	235	60	–	[133]
Cs₃BiCl₆:Mn²⁺	NC	607	80	174	20	2.5% (λ_ex = 430 nm)	[18]

PL, photoluminescence; SC, single crystal; NC, nanocrystal; PLQY, PL quantum yield; FWHM, full width at half maximum.

Table 8. The key PL properties of A₃REX₆ (including PL peak, decay time, and PLQY)

Compound	Sample	PL peak (nm)	Decay time (μs)	PLQY at λ_ex	Ref.
Cs₃ScCl₆:Sb³⁺	NC	545	3.6	32% (λ_ex = 345 nm)	[143]
Cs₃ScCl₆:Sb³⁺	NC	555	–	48% (λ_ex = 365 nm)	[143]
Cs₃YCl₆:Sb³⁺	Powder	550	2.37	93.5% (λ_ex = 345 nm)	[72]
Cs₃YCl₆:Sb³⁺	NC	545	3.9	26% (λ_ex = 320 nm)	[142]
Cs₃LaCl₆:Sb³⁺	NC	570	5.4	30% (λ_ex = 320 nm)	[142]
Cs₃La_0.17Nd_0.83Br₆	NC	1,070, 1,350	290	64.65% (λ_ex = 405 nm, NIR)	[144]
Cs₃LaI₆:Er³⁺	NC	1,540	6,670	7.8% (λ_ex = 370 nm)	[187]

PL, photoluminescence; NC, nanocrystal; PLQY, PL quantum yield; NIR, near infrared.

Table 9. The key PL properties of A₃LnX₆ (including PL peak, decay time, and PLQY)

Compound	Sample	PL peak (nm)	Decay time (ns)	PLQY at λ_ex	Ref.
Cs₃CeCl₆	SC	380, 410	13.61 (2.93%)	99.89% (λ_ex = 365 nm)	[199]
Cs₃CeCl₆	SC	380, 410	40.75 (97.07%)	99.89% (λ_ex = 365 nm)	[199]
Cs₃CeBr₆	Powder	392, 421	29.1	80% (λ_ex = 365 nm)	[185]
Cs₃CeBr₆	Powder	390, 421	28.33 (390 nm)	89.94% (λ_ex = 365 nm)	[15]
Cs₃CeBr₆	Powder	390, 421	28.67 (421)	89.94% (λ_ex = 365 nm)	[15]
Cs₃CeBr₆	Powder	391, 421	28.7 (391 nm)	92.5% (λ_ex = 350 nm)	[73]
Cs₃CeBr₆	Powder	391, 421	27.1 (425 nm)	92.5% (λ_ex = 350 nm)	[73]
Cs₃CeBr₆	SC	395, 425	8.06 (3.06%)	92.57% (λ_ex = 365 nm)	[199]
Cs₃CeBr₆	SC	395, 425	43.53 (96.94%)	92.57% (λ_ex = 365 nm)	[199]
Cs₃CeI₆	SC	427, 470	45.44	7.53% (λ_ex = 365 nm)	[199]
Cs₃CeI₆	Powder	430, 470	26.1	76.2% (λ_ex = 365 nm)	[13]
Rb₃CeI₆	Film	427, 468	22.3 (472 nm)	51% (λ_ex = 280 nm)	[186]
Rb₃CeI₆	Film	427, 468	25 (468 nm)	51% (λ_ex = 280 nm)	[186]
Cs₃CeCl₆:Gd³⁺	NC	376, 408	42.8	96% (λ_ex = 365 nm)	[155]
Cs₃EuCl₆	Powder	592, 614	4.35 × 10⁶ (λ_ex = 334 nm)	92.4% (λ_ex = 365 nm)	[158]
Cs₃EuCl₆	Powder	592, 614	4.11 × 10⁶ (λ_ex = 465 nm)	92.4% (λ_ex = 365 nm)	[158]
Cs₃EuCl₆	NC	590, 611, 652, 700	3.99 × 10⁶	48.78% (λ_ex = 280 nm)	[147]
Cs₃EuCl₆	NC	430	25.79	5.38% (λ_ex = 350 nm)	[147]
EHC–Cs₃EuCl₆	NC	617	3.09 × 10⁶	92.4% (λ_ex = 365 nm)	[150]

PL, photoluminescence; SC, single crystal; NC, nanocrystal; PLQY, PL quantum yield.

Table 10. The key PL properties of A₃LnX₆ (including PL peak, FWHM, Stokes shift, decay time and PLQY)

Compound	Sample	PL peak (nm)	FWHM (nm)	Stokes shift (nm)	Decay time	PLQY at λ_ex	Ref.
Cs₃TbCl₆	Powder	547	–	–	6.8 ms	90.8% (λ_ex = 280 nm)	[83]
Cs₃DyI₆	NC	488, 574, 660, 1,540	92	118	–	–	[187]
Cs₃TmCl₆	NC	440	88	70	1.5 ns (76.6%)	22.8% (λ_ex = 370 nm)	[27]
Cs₃TmCl₆	NC	440	88	70	7.1 ns (23.4%)	22.8% (λ_ex = 370 nm)	[27]
Cs₃YbCl₆	NC	429	–	–	1–2 ns (93%)	89.3% (λ_ex = 355 nm)	[139]
Cs₃YbCl₆	NC	429	–	–	8–9 ns (7%)	89.3% (λ_ex = 355 nm)	[139]
Cs₃GdCl₆:Sb³⁺	NC	550	–	–	4.1 μs	28% (λ_ex = 320 nm)	[142]
Cs₃GdCl₆:Sb³⁺	Powder	540	120	–	2.96 μs	96.3% (λ_ex = 330 nm)	[22]
Cs₃TbCl₆:Sb³⁺	NC	450, 489, 548, 621, 700	8.6	225	7.6 ms	48.18% (λ_ex = 280 nm)	[16]
Cs₃Tb_0.1Ce_0.9Cl₆	NC	470, 405, 546	–	–	33.04 ns (405 nm)	86% (λ_ex = 290 nm)	[171]
Cs₃DyI₆:Er³⁺	NC	488, 574, 660, 1,540	–	–	9.7 ns	87.4% (λ_ex = 370 nm)	[187]
Cs₃YbCl₆:Sb³⁺	SC	533	120	206	1.66 μs	66.9% (λ_ex = 365 nm)	[165]
Cs₃LuCl₆:Sb³⁺	NC	525	–	–	2.8 μs	13% (λ_ex = 320 nm)	[142]
Cs₃LuCl₆:Sb³⁺	NC	531	104	191	1.96 μs	92% (λ_ex = 340 nm)	[167]
Cs₃LuCl₆:Sb³⁺	Powder	380, 420	–	30, 70	33.76 ns (380 nm)	82.02% (λ_ex = 350 nm)	[188]
Cs₃LuCl₆:Sb³⁺	Powder	380, 420	–	30, 70	34.11 ns (420 nm)	82.02% (λ_ex = 350 nm)	[188]
Cs₃LuCl₆:Ce³⁺	Powder	382	57	42	26.6 ns	6% (λ_ex = 335 nm)	[189]
Cs₃LuCl₆:Tb³⁺	Powder	549	12	275	–	62% (λ_ex = 335 nm)	[189]
Cs₃LuCl₆:Ce³⁺, Sm³⁺	Powder	379	26	39	18.7 ns	5% (λ_ex = 335 nm)	[189]

PL, photoluminescence; SC, single crystal; NC, nanocrystal; PLQY, PL quantum yield; FWHM, full width at half maximum.

Fig. 1. A-site cations, B-site cations, and X-site halogen anions of A₃BX₆ metal halide perovskites (MHPs) are illustrated in the periodic table. (C, H, O, and N form organic groups occupying the A-site). The blue–gray dashed box denotes P-block elements; the teal–gray dashed box represents rare-earth elements with empty f orbitals; the light-olive dashed box indicates light rare-earth elements with f orbitals; and the sand-yellow dashed box corresponds to heavy rare-earth elements with f orbitals.

Fig. 2. (A) The band-edge luminescence mechanism diagram of CsPbBr₃. (B) The luminescence process triggered by different excitation sources. GS, ground state. (C) The luminescence mechanism of self-trapped exciton (STE) (including intrinsic STE and STE caused by doping). (D) The luminescence mechanism of transition-metal-doped luminescent ions (Mn²⁺, Mn⁴⁺, and Cr³⁺). (E) The d–f/f–f transition mechanism of rare earth.

Fig. 3. (A) The transformation between a regular octahedron [InCl₆]³⁻ and distorted octahedron [InX₅OH₂]²⁻. Adapted with permission [87]. Copyright 2020, published by Wiley-VCH. (B) The photoluminescence (PL) and PL excitation (PLE) of pure A₃InCl₆ synthesized from methanol. MeOH, methanol. Adapted with permission [89]. Copyright 2021, published by Wiley-VCH. (C) The PL and PLE of the coexisting samples of A₃InCl₆ and A₂InX₅·H₂O were synthesized using hydrochloric acid. Adapted with permission [89]. Copyright 2021, published by Wiley-VCH. (D) Schematic of the photophysical processes in Cs₃InBr₆. Adapted with permission [71]. Copyright 2021, published by Royal Society of Chemistry. (E) Configurational coordinate diagram illustrating the origin of PL in Cs₂InBr₅·H₂O. ISC, intersystem crossing. Adapted with permission [78]. Copyright 2019, published by Wiley-VCH. (F) The dehydrated mixture is contained in the tetrahydrofuran solution. The luminescence phenomenon of different water volumes (0 to 0.05%, v/v). Adapted with permission [78]. Copyright 2019, published by Wiley-VCH. (G) Schematic illustrations of the relaxation mechanisms of the self-trapped excitons (STEs) in phase I (left) and phase II (right). Ex, excitation; GS, ground state. Adapted with permission [23]. Copyright 2021, published by Wiley-VCH.

Fig. 4. (A) Photoluminescence (PL) excitation (PLE) spectra of Rb₃InCl₆:Sb³⁺ collected at room temperature (RT) and 80 K. Adapted with permission [96]. Copyright 2022, published by American Chemical Society. (B) The photophysical process of Rb₃InCl₆:Sb³⁺. GS, ground state. Adapted with permission [96]. Copyright 2022, published by American Chemical Society. (C) Peak-fitted PL spectra of K₃InCl₆:Sb³⁺. Adapted with permission [97]. Copyright 2024, published by Wiley-VCH. (D) Photographs of the white light-emitting diode (LED) based on Rb₃InCl₆:Sb³⁺ at low current (left) and high current (right). Adapted with permission [67]. Copyright 2024, published by American Chemical Society. (E) Reversible fluorescence switching between Cs₂InCl₅·H₂O:Te⁴⁺ and Cs₃InCl₆:Te⁴⁺. Adapted with permission [88]. Copyright 2023, published by Academic Press Inc. (F) The LED color changes as the temperature is monitored from 300 to 350 K using a temperature gun. Adapted with permission [92]. Copyright 2025, published by Royal Society of Chemistry. (G) Corresponding absolute sensitivity (S_a) and (H) relative sensitivity (S_r) values of Cs₂InCl₅·H₂O:xBi³⁺. Adapted with permission [93]. Copyright 2024, published by Elsevier.

Fig. 5. (A) Proposed photoluminescence (PL) mechanism of Sb³⁺/Mn²⁺-codoped Cs₃InCl₆ NCs. Adapted with permission [102]. GS, ground state; ES, excited state; Abs, absorption. Copyright 2024, published by American Chemical Society. (B) Emission spectra of Cs₃InCl₆:3% Sb³⁺ and Cs₃InCl₆:3% Sb³⁺, 15% Mn²⁺-based light-emitting diodes (LEDs) under 317-nm chip excitation. Adapted with permission [102]. Copyright 2024, published by American Chemical Society. (C) Schematic diagram of Cs₃InCl₆:Sb³⁺,Ln³⁺ (Ln³⁺ = Nd³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, and Yb³⁺). Adapted with permission [50]. Copyright 2023, published by Wiley-VCH. (D) Images of security patterns made of Cs₃InCl₆:1% Sb³⁺,50% Eu³⁺ nanocrystals (NCs). Adapted with permission [50]. Copyright 2023, published by Wiley-VCH. (E) PL spectra and patterns for the Cs₂InCl₅·H₂O:Bi³⁺,Mn²⁺. Adapted with permission [103]. Copyright 2023, published by American Chemical Society. (F) Radioluminescence (RL) spectra of Rb₃InCl₆:Sb³⁺ and Bi₄Ge₃O₁₂ (BGO) under x-ray excitation. Adapted with permission [68]. Copyright 2025, published by Elsevier. (G) Modulation transfer function (MTF) curves of the film of Rb₃InCl₆:Sb³⁺ NC and polysulfone. Adapted with permission [68]. Copyright 2025, published by Elsevier. (H) RL intensity of Rb₃InCl₆:Sb³⁺ under continuous x-ray irradiation. Adapted with permission [68]. Copyright 2025, published by Elsevier. (I) The RL spectra of Rb₃InCl₆:Sb³⁺, Cs₂KInCl₆:Sb³⁺, and Cs₂NaInCl₆:Sb³⁺ with increasing cumulative dose up to 500 Gy. Adapted with permission [65]. Copyright 2021, published by American Chemical Society.

Fig. 6. (A) Absorption and photoluminescence (PL) spectra of K₃SbCl₆ nanocrystals (NCs) at different synthesized temperatures. Adapted with permission [104]. Copyright 2021, published by Elsevier. (B) Electrical–optical–electrical (EOE) frequency response of the [Na(DMSO)₂]₃SbBr₆-based optical converter [109]. DSO, digital storage oscilloscope; PD, photodetector. Copyright 2022, published by Wiley-VCH. (C) The EOE frequency response. Adapted with permission [109]. Copyright 2022, published by Wiley-VCH. (D) Temperature-dependent decay time for [C@Cs]₂CsSbBr₆ and its derivatives. Adapted with permission [110]. Copyright 2020, published by American Chemical Society. (E) Correlation between shortest Sb–Sb distances and PL quantum yield (PLQY) for 0D Sb³⁺-based halides. (Among them, A is (gua-DPG)₃SbCl₆ [74], B is [Bzmim]₃SbCl₆ [118], C is (PMA)₃SbBr₆ [112] , D is [DMPZ]₂SbCl₆·Cl·(H₂O)₂ [182], E is [Prmim]₃SbCl₆ [113], F is [Hmim]₃SbCl₆ [113], and G is H₃SbBr₆(L)₆ [183].) Adapted with permission. Copyright 2023, published by American Chemical Society. The information encryption and decryption process for (F) panda pattern and (G) Chinese character, respectively. Adapted with permission [116]. Copyright 2022, published by Elsevier.

Fig. 7. (A) Structural transformation between [Bzmim]₃SbCl₆ and [Bzmim]₂SbCl₅. Adapted with permission [118]. Copyright 2019, published by Wiley-VCH. (B) Digital photographs of the paper before and after heating under 390-nm ultraviolet (UV) light, with words written using [Bzmim]Cl and SbCl₃ inks. Vis, visible. Adapted with permission [117]. Copyright 2025, published by Royal Society of Chemistry. (C) Schematic of the laser-based encryption/decryption process: (I) Printing the paper with a laser engraver; (II) blacking out in a moist environment; (III) aging at 353 K for initialization; (IV) heating at 353 K; and (V) keeping in moisture for 6 h [118]. Copyright 2019, published by Wiley-VCH. (D) The radioluminescence (RL) and light yield (L.Y.) of Bzmim₃SbCl₆. Adapted with permission [119]. Copyright 2024, published by Wiley-VCH. (E) The x-ray images of a standard resolution pattern plate and an earphone based on [Bzmim]₃SbCl₆@PMMA as the scintillator. Adapted with permission [119]. Copyright 2024, published by Wiley-VCH. (F) Modulation transfer function (MTF) curve of the [Bzmim]₃SbCl₆@PMMA scintillator film. Adapted with permission [119]. Copyright 2024, published by Wiley-VCH. (G) Configuration of Gua₃SbCl₆ supercell. Adapted with permission [121]. Copyright 2023, published by Wiley-VCH. (H) RL spectra of Gua₃SbCl₆ and Bi₄Ge₃O₁₂ (BGO). Adapted with permission [121]. Copyright 2023, published by Wiley-VCH. (I) L.Y. of Gua₃SbCl₆ under ⁵⁷Co γ-ray excitation. Adapted with permission [121]. REL, relative emission intensity; ABS, absorption. Copyright 2023, published by Wiley-VCH.

Fig. 8. (A) Schematic diagram of the photodetector based on Cs₃BiBr₆. Adapted with permission [123]. Copyright 2019, published by Royal Society of Chemistry. (B) Comparison of the detectivity at 2 different light densities. Adapted with permission [123]. Copyright 2019, published by Royal Society of Chemistry. (C) Transmission electron microscopy image for Cs₃BiBr₆ and Cs₃Bi₂Br₉ interface. Adapted with permission [127]. Copyright 2022, published by Wiley-VCH. (D) Responsivity and detectivity spectra of Cs₃BiBr₆/Cs₃Bi₂Br₉ bulk. Adapted with permission [124]. Copyright 2022, published by Wiley-VCH. (E) Schematic diagram and effective digital data for encrypted photocommunication based on Cs₃BiCl₆/GaN heterojunction. Adapted with permission [128]. Copyright 2025, published by Wiley-VCH. (F) Fitting results of temperature-dependent full width at half maximum (FWHM) for Rb₃BiCl₆ and Rb₃BiCl₆:4.5% Sb³⁺. Adapted with permission [33]. Copyright 2021, published by Wiley-VCH. (G) Absorption, photoluminescence (PL), and PL excitation (PLE) spectra of Cs₃BiCl₆ nanocrystals (NCs). Adapted with permission [122]. Copyright 2020, published by Springer. (H) X-ray induced radioluminescence (RL) of Cs₃BiCl₆ single crystal. Adapted with permission [125]. Copyright 2016, published by Elsevier. (I) Pulsed x-ray induced decay profile of Cs₃BiCl₆ single crystal. Adapted with permission [125]. Copyright 2016, published by Elsevier. (J) Pulse-height spectra of Gd₂SiO₅:Ce³⁺ (GSO) and Cs₃BiCl₆ under ¹³⁷Cs γ-ray excitation. Adapted with permission [125]. Copyright 2016, published by Elsevier.

Fig. 9. (A) Photoluminescence (PL) spectra of Cs₂ScCl₅·H₂O at room temperature with different excitation wavelengths. Adapted with permission [140]. Copyright 2022, published by Wiley-VCH. (B) The frontier molecular orbital energies of the lowest electronic transitions involving the [SbCl₆]³⁻ octahedron upon symmetric percentage of elongation of Sb–Cl. Adapted with permission [142]. Copyright 2024, published by Elsevier. (C) Excitation and emission spectra of Cs₃ScCl₆:Sb³⁺ nanocrystals (NCs). Adapted with permission [143]. Copyright 2023, published by Wiley-VCH. (D) Photographic images of white light-emitting diode (LED) of Cs₃ScCl₆:Sb³⁺ at different applied currents. Adapted with permission [143]. Copyright 2023, published by Wiley-VCH. (E) Photographic images of fabricated white LED device of Cs₃LaCl₆:Sb³⁺ NCs at different applied current fluxes. Adapted with permission [142]. Copyright 2024, published by Elsevier. (F) Photocurrent generated by x-ray irradiation at various dose rates under 30-V bias. Adapted with permission [145]. Copyright 2023, published by American Chemical Society. (G) Linear relationship between signal-to-noise ratio value and x-ray dose rate. Adapted with permission [72]. Copyright 2025, published by Springer. (H) The photograph of the standard line-pair card under the visible light (left) and the corresponding x-ray image of the standard line-pair card (right). Adapted with permission [72]. Copyright 2025, published by Springer.

Fig. 10. (A) Photoluminescence (PL) and PL excitation (PLE) spectra of Cs₃ScCl₆:Ce³⁺ crystals. Em, emission; Ex, excitation. Adapted with permission [135]. Copyright 2020, published by Elsevier. (B) X-ray excited emission spectra of pure Cs₂LiYCl₆ (solid line), Cs₂LiYCl₆:Ce³⁺ (dashed line), and Li₃YCl₆:Ce³⁺ (dashed–dotted line), recorded at room temperature. The inset displays the same spectra plotted with a logarithmic Y axis. The emission intensity of the 3 crystals was normalized at 300 nm. Adapted with permission [146]. Copyright 1999, published by Elsevier. (C) Radioluminescence (RL) spectra comparison of Cs₃LaCl₆:2% Ce at 50 and 500 K. Adapted with permission [136]. Copyright 2015, published by Elsevier. (D) RL spectra comparison of Cs₃LaBr₆:2% Ce at 50 and 500 K. Adapted with permission [136]. Copyright 2015, published by Elsevier. (E) Scheme of Ce³⁺ emission and excitation. Adapted with permission [136]. Copyright 2015, published by Elsevier. (F) Pulse-height spectra of Gd₂SiO₅:Ce³⁺ (GSO) and Cs₃ScCl₆:Ce³⁺ under ¹³⁷Cs γ-ray excitation. Adapted with permission [135]. Copyright 2020, published by Elsevier. Pulse height spectrum measured on (G) Cs₃LaCl₆:Ce³⁺ and (H) Cs₃LaBr₆:Ce³⁺ single crystal under ¹³⁷Cs excitation, respectively. A commercial NaI:Tl crystal is used as the reference. Adapted with permission [58]. Copyright 2014, published by Elsevier. (I) Pulsed x-ray measurements of luminosities for Cs₃LaI₆ containing different Ce concentrations. Adapted with permission [58]. Copyright 2014, published by Elsevier.

Fig. 11. (A) Photoluminescence (PL) Photographs of Cs₃EuCl₆ and Cs₃TbCl₆ nanocrystal (NC) films under excitation wavelengths from 260 to 360 nm with a 10-nm interval. Adapted with permission [147]. Copyright 2023, published by Royal Society of Chemistry. (B) Photographs of anticounterfeiting marks formed by transfer printing under ambient, 254-nm, and 365-nm ultraviolet (UV) lights. Adapted with permission [147]. Copyright 2023, published by Royal Society of Chemistry. (C) Current density–voltage and luminance–voltage curves. Adapted with permission [150]. Copyright 2024, published by Wiley-VCH. (D) external quantum efficiency (EQE)–current density curves of Cs₃LaCl₆, Cs₃EuCl₆, and Cs₃TbCl₆ light-emitting diode (LEDs). Adapted with permission [150]. Copyright 2024, published by Wiley-VCH. (E) The phase diagrams of CeBr₃–CsBr binary system. Adapted with permission [73]. Copyright 2021, published by Royal Society of Chemistry. (F) PL spectra of CsCe₂Br₇ single crystals at 38 K. Adapted with permission [151]. Copyright 2015, published by American Chemical Society. (G) The EQE–voltage curve of Cs₃CeBr₆ LED. Adapted with permission [73]. Copyright 2021, published by American Chemical Society. (H) Spectrum of the white LED under forwarding voltage. The inset plot shows the photograph of the white LED device. Adapted with permission [73]. Copyright 2021, published by American Chemical Society.

Fig. 12. (A) Photoluminescence (PL) spectra of Cs₃CeBr₆, Cs₃CeBr₂I₄, and Cs₃CeI₆, with the inset showing the corresponding photographs under ultraviolet (UV) light radiation. Adapted with permission [13]. Copyright 2022, published by American Association for the Advancement of Science. (B) Voltage–luminance curves of Cs₃CeI₆ light-emitting diode (LEDs). Adapted with permission [13]. Copyright 2022, published by American Association for the Advancement of Science. (C) External quantum efficiency (EQE)–luminance curves of Cs₃CeI₆ LEDs. Adapted with permission [13]. Copyright 2022, published by American Association for the Advancement of Science. (D) Schematic diagram of Cs₃CeI₆ energy band structure and 2 types of excitons. Adapted with permission [14]. Copyright 2024, published by Springer Nature. (E) EQE–luminance curve of Cs₃CeI₆ control and Cs-rich devices. Adapted with permission [14]. Copyright 2024, published by Springer Nature. (F) Current density–voltage–luminance curve of Cs₃CeI₆ control and Cs-rich devices. Adapted with permission [14]. Copyright 2024, published by Springer Nature.

Fig. 13. (A) The logarithmic curve of light-intensity-dependent photocurrent density and corresponding power law fit curve under 320-nm light illumination. LDR, linear dynamic range. Adapted with permission [15]. Copyright 2024, published by Elsevier. (B) Responsivity and detectivity of the optimum photodetector versus the light intensity. Adapted with permission [15]. Copyright 2024, published by Elsevier. (C) Spectral responsivity and specific detectivity of 0% and 20% Gd³⁺-alloyed CCGC photodetector. Adapted with permission [155]. Copyright 2024, published by Wiley-VCH. (D) J–V curves of 0% and 20% Gd³⁺-alloyed CCGC photodetector in illumination (310 nm) in solid line and dark conditions in dashed line. Adapted with permission [155]. Copyright 2024, published by Wiley-VCH. (E) Radioluminescence intensity of the (MTP)₃EuCl₆ glass after high-dose irradiation, followed by heating at 150 °C for 1 h to restore scintillation performance. Adapted with permission [159]. Copyright 2025, published by Wiley-VCH. (F) Image of a polished slice of Cs₃CeCl₆ showing good transparency needed for efficient light emission. Adapted with permission [160]. Copyright 2013, published by Institute of Electrical and Electronics Engineers. (G) Pulse-height spectra of Cs₃CeCl₆ single crystals under excitation from 662-keV photons from a ¹³⁷Cs source. Adapted with permission [160]. Copyright 2013, published by Institute of Electrical and Electronics Engineers. (H) Pulsed x-ray-excited scintillation decay time profile of Cs₃PrCl₆. Adapted with permission [163]. Copyright 2022, published by M Y U Scientific Publishing Division. (I) ¹³⁷Cs γ-ray induced scintillation pulse height spectra of the Cs₃PrCl₆ and a reference Bi₄Ge₃O₁₂ (BGO) crystal. Adapted with permission [163]. PH, pulse height. Copyright 2022, published by M Y U Scientific Publishing Division.

Fig. 14. (A) Photoluminescence (PL) spectrum of the fabricated white light-emitting diode (LED) prepared by Cs₃TmCl₆. Adapted with permission [27]. Copyright 2024, published by American Chemical Society. (B) Long-term running test showing the T₅₀ of the white LED. Adapted with permission [27]. Copyright 2024, published by American Chemical Society. (C) Emission spectrum of the white LED device fabricated by blending the yellowish-emitting Cs₃GdCl₆:1.0% Sb³⁺ powder with the commercial BaMgAl₁₀O₁₇:Eu²⁺ and K₂SiF₆:Mn⁴⁺ on a 365-nm chip. Adapted with permission [22]. Copyright 2024, published by Royal Society of Chemistry. (D) Integrated PL intensities of the Cs₃GdCl₆:Sb³⁺ MCs as a function of temperature. Adapted with permission [22]. Copyright 2024, published by Royal Society of Chemistry. (E) The in situ dynamic emission color transformation of Cs₂YbCl₅·H₂O:Sb³⁺ to Cs₃YbCl₆:Sb³⁺ by methanol. Adapted with permission [165]. Copyright 2024, published by Wiley-VCH. (F) Estimated luminosity of polycrystalline samples (Cs₂NaGdCl₆:Ce³⁺, Cs₃GdCl₆:Ce³⁺, Cs₂NaGdBr₆:Ce³⁺, and Cs₃GdBr₆:Ce³⁺) under x-ray irradiation versus Ce concentration. Adapted with permission [32]. Copyright 2014, published by Elsevier. (G and H) γ-Ray pulse height spectra of Cs₃GdCl₆:Ce³⁺ and Cs₃GdBr₆:Ce³⁺, respectively. Adapted with permission [32]. Copyright 2014, published by Elsevier.

Fig. 15. (A) The charge–carrier dynamics model and photophysical processes of Cs₃TbCl₆:Sb³⁺ nanocrystals (NCs). (1) Transfer process assisted by Cl⁻-Tb³⁺ charge transition in [TbCl₆]³⁻; (2) thermally boosting energy transfer (ET) assisted by [SbCl₆]³⁻-induced self-trapped exciton (STE) state. Adapted with permission [16]. Copyright 2024, published by Wiley-VCH. (B) The variation of detection limit of Cs₃TbCl₆:Sb³⁺ NCs as a function of Sb/Tb ratio. Adapted with permission [16]. Copyright 2024, published by Wiley-VCH. (C) Modulation transfer function (MTF) of x-ray images from undoped and Sb³⁺-doped Cs₃TbCl₆ NCs. Adapted with permission [16]. Copyright 2024, published by Wiley-VCH. (D) Ce³⁺ to Tb³⁺ ET process in Cs₃Tb_xCe_1-xCl₆ alloy NCs. Adapted with permission [171]. Copyright 2024, published by Wiley-VCH. (E) Commission Internationale de l’Éclairage (CIE) coordinate of white light-emitting diode (LED) based on Cs₃Tb_0.5Ce_0.5Cl₆. Adapted with permission [142]. Copyright 2024, published by Wiley-VCH. (F) Emission spectra of Cs₃TbF₆:Eu³⁺ crystals before and after water treatment. Adapted with permission [169]. Copyright 2022, published by American Chemical Society. (G) Luminescence photographs of the orange pattern under 365-nm ultraviolet (UV) lamp excitation in a wetting–drying cycle. Adapted with permission [169]. Copyright 2022, published by American Chemical Society. (H) The encryption of ACSII binary codes and decryption process. Adapted with permission [168]. Copyright 2024, published by Wiley-VCH.

Fig. 16. (A) The linear response between radioluminescence (RL) intensity and x-ray dose rate of Cs₃TbCl₆ and Rb₃TbCl₆ under low-dose-rate excitation. Their detection limits can be defined, as the signal-to-noise ratio (SNR) is 3. Adapted with permission [31]. Copyright 2022, published by American Chemical Society. (B) Spatial resolution measurement of Cs₃TbCl₆, Rb₃TbCl₆, and Gd₂O₂S scintillator films. Adapted with permission [31]. Copyright 2022, published by American Chemical Society. (C) The linear relationship between SNR value of Cs₃TbCl₆ and x-ray dose rate. Adapted with permission [83]. Copyright 2025, published by Springer. (D) The photograph of a smartphone (left) the standard line-pair card under the visible light (top) and the corresponding x-ray image of the standard line-pair card (bottom). Adapted with permission [83]. Copyright 2025, published by Springer. (E) Transmission spectra of Bzmim₃LnCl₆ glass. Adapted with permission [172]. Copyright 2025, published by Wiley-VCH. (F) Spatial resolution of the Bzmim₃TbCl₆ glass scintillation demonstrated using a line pair card. Adapted with permission [172]. Copyright 2025, published by Wiley-VCH.

Fig. 17. (A) Workflow of computational exploration for inorganic halide perovskite derivatives. Adapted with permission [174]. Copyright 2022, published by American Chemical Society. (B) Radiographic imaging and tomography (RadIT) metrics and scintillator metrics are correlated through the energy and data (information) flows. Adapted with permission [175]. PSF, point spread function; LSF, line spread function; DQE, detective quantum efficiency; NEP, noise equivalent power. Copyright 2023, published by Institute of Electrical and Electronics Engineers Inc. (C) Empirical trend between light yield and material’s bandgap for a range of scintillator compounds. Adapted with permission [184]. Copyright 2002, published by Elsevier. (D) Trends of experimentally reported light yield (L.Y.) with density functional theory (DFT)-computed bandgaps and (E) averaged ionic part of the dielectric constants. Adapted with permission [176]. Copyright 2019, published by Springer.

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