Lead halide perovskites have attracted much attention in optoelectronic research due to their exceptional properties, such as long carrier diffusion lengths, low exciton binding energies, and cost-effective production. However, their inherent lead toxicity and poor environmental stability have challenges, restricting their wider adoption. It is thus important to search for safer, lead-free alternatives. Cesium copper halides emerge as promising candidates, offering the similar photoluminescent properties and potential for full-spectrum emission. Nevertheless, these materials still suffer from degradation under harsh conditions, which limits their practical use. Embedding cesium copper halides in glass matrices can enhance the stability via protecting the quantum dots from environmental factors like moisture and oxygen. However, challenges such as low transparency and limited tunability remain. To overcome these issues, the introduction of rare-earth ions like europium (Eu²⁺/Eu³⁺) into the glass matrix is proposed. In this work, transparent Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ dual-phase quantum dot glass was synthesized by an one-step melt-quenching method. The resulting glass exhibits a full-spectrum cold white light emission with a correlated color temperature (C) of 7 421 K, a general color rendering index (R) of 82, and a photoluminescence quantum yield of 75.1%.

In this study, a transparent Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ biphasic quantum dot glass was synthesized by an one-step melt-quenching method. The glass composition designed was 20% SiO₂, 50% B₂O₃, 5% ZnO, 3% Al₂O₃, 10% Cs₂CO₃, and 12% NaI, all in molar percentages. To induce the precipitation of biphasic quantum dots within the glass matrix, additional components were introduced, i.e., 1% CuI to promote the formation of cesium copper iodide, 0.04% SnO to prevent the oxidation of Cu⁺, 1% CaO to facilitate the precipitation process, and 1% MnO to reduce the viscosity of the glass. Various concentrations of Eu₂O₃ (i.e., 0%, 0.02%, 0.05%, and 0.10%) were added to enhance the glass emission properties.

The crystalline phases in the glass were determined by X-ray diffraction (XRD). The glass transition temperature and crystallization temperature were determined by differential scanning calorimetry (DSC) as indicatives of the thermal stability of the glass. The photoluminescence (PL) spectra were employed to evaluate the optical properties of the glass (i.e., the emission spectrum, quantum yield, and R). The oxidation states of the elements within the glass were analyzed by X-ray photoelectron spectroscopy, providing an insight into the distribution of Eu²⁺/Eu³⁺. The absorption spectra of the glass were characterized by UV-visible spectrophotometry.

The results demonstrate that the Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ biphasic quantum dot glass exhibits enhanced photoluminescent properties, compared to the undoped samples. The introduction of Eu₂O₃ can increase the overall emission intensity and broaden the emission spectrum, resulting in a full-spectrum cold white light emission. Specifically, the glass doped with 0.05% Eu₂O₃ achieves a photoluminescence quantum yield of 75.1%, with a C of 7421 K and a general R of 82. These results indicate that the Eu²⁺/Eu³⁺ co-doping effectively improves the glass emission characteristics via providing additional emission centers in the blue and red regions of the spectrum, attributed to Eu²⁺ and Eu³⁺, respectively. The structural analysis shows the effective incorporation of Eu²⁺/Eu³⁺ ions into the Cs₃Cu₂I₅/CsCu₂I₃ matrix without disrupting the existing crystal structures. The XRD patterns indicate that the doped glass maintains the characteristic diffraction peaks of Cs₃Cu₂I₅ and CsCu₂I₃, indicating that the addition of Eu₂O₃ does not alter the fundamental crystal structure of the biphasic quantum dots. Moreover, the DSC analysis reveal a high glass transition temperature of 652 K and a crystallization temperature of 717 K, indicating that the doped glass has an excellent thermal stability. The glass samples are also subjected to long-term stability tests, showing a minimal degradation in their optical properties after three months of storage. The photoluminescence spectra of the stored samples exhibit only minor shifts in emission peak positions and intensity, indicating that the glass retains its luminescent properties. In addition, the Eu²⁺/Eu³⁺ doping also improves the glass transparency and color rendering capabilities. The doped glass samples have a higher degree of transparency, compared to the undoped samples, which is attributed to the clarifying effect of Eu₂O₃. The Eu²⁺/Eu³⁺ ions provide complementary blue and red emission, thus enhancing the overall color rendering and allowing for the production of cold white light with a high color quality. The improved transparency and color rendering make the doped glass suitable for use in lighting and display applications in which high brightness and accurate color representation are required.

Eu²⁺/Eu³⁺ doped Cs₃Cu₂I₅/CsCu₂I₃ biphasic quantum dot glass was synthesized as a stable, lead-free photoluminescent material. The synthesized glass demonstrated an excellent full-spectrum cold white light emission, making it a promising candidate for various optoelectronic applications (i.e., lighting, displays, and sensors). The one-step melt-quenching method was effective in producing a material with a high thermal stability, a robust structural integrity and an enhanced optical performance. The introduction of Eu₂O₃ provided additional emission centers, improved transparency, and enhanced color rendering, addressing the limitations of previous cesium copper halide quantum dot glasses. This study could provide a viable strategy for the design and fabrication of advanced quantum dot glasses that meet the stringent demands of modern optoelectronic devices, offering a safer and more stable alternative to lead-based perovskites.