Blast furnace slag is a type of bulk solid waste generated by the iron and steel industry. The high value-added utilization of blast furnace slag has been the focus of research in the relevant industries, which is of great significance to the green development of the steel industry. This work focuses on blast furnace slag and reviews the progress of its use as a photocatalytic material for wastewater treatment in the last five years. Firstly, we introduce the basic information of blast furnace slag, such as the formation and mineral composition of blast furnace slag, the feasibility of using it as a photocatalytic material, the current situation of comprehensive utilization at home and abroad, and the problems in comprehensive utilization. Secondly, the current status of photocatalytic technology is briefly explained, covering its mechanism of action, performance improvement methods and development trends. Then, the progress of research on blast furnace slag as a photocatalytic material for wastewater purification is described. The existing literature on the factors affecting its photocatalytic efficiency and ways to improve it are discussed. Finally, the treatment and application of blast furnace slag-based photocatalytic materials are summarized, and its sustainable resource utilization is also prospected.

The existing mechanoluminesence has a single band. The ³P₁→¹S₀ transition of Bi³⁺ ion can achieve an ultrabroadband emission in UV-Visible. However, the existing Bi³⁺ ion activated mechanoluminesence materials only emit blue light. To solve this problem, the UV-Visible-NIR ultrabroadband mechanoluminesence is realized in a multi-lattice garnet compound matrix, and its mechanoluminesent performance is regulated by the neighbor ion (i.e., Sc³⁺ ion) substitution strategy. The luminescence source is determined by steady-state fluorescence spectroscopy (at 465 nm, corresponding to the ³P₁→¹S₀ transition of Bi³⁺ ion). The mechanism of mechanoluminesence is related to the persistent luminescence. The material defect distribution is obtained by thermoluminescence test, and the deep trap (>0.7 eV) contributes to the mechanoluminesence.

Mn²⁺ doped garnet-type Na₂CaSn₂Ge₃O₁₂ phosphor was selected and studied due to its abundant chemical compositions and several crystallographic sites. Several ion substitution strategies including the chemical substitution of Na⁺/Sr²⁺/Ba²⁺ on Ca²⁺ sites and the anti-site occupation of Sn⁴⁺/Ge⁴⁺ were designed for regulating the different energy traps and promoting multimode luminescence properties like persistent luminescence, X-ray storage capacities and mechano-luminescence. In addition, the X-ray luminescence storage and mechano-luminescence properties of these materials as well as their applications on X-ray luminescence extension imaging and stress sensing were also investigated.

Compared with conventional destructive mechanoluminescent materials, trap-controlled mechanoluminescent materials generally preserve high structural integrity and repeatability during the mechanoluminescent process. The trap-controlled mechanoluminescent materials have attracted recent attention in diverse fields of stress sensors, mechano-driven lighting and displays. The development of high-performance trap-controlled mechanoluminescent materials is of great significance to promote the application of mechanoluminescence. This paper was to investigate a trap-controlled reproducible mechanoluminescent material, i.e., Ca₂Ga₂GeO₇:Pr³⁺, and analyze its luminescent properties by the measurements of X-ray diffraction patterns, diffuse reflection spectra, phosphorescent decay curves, photoluminescence, mechanoluminescence and thermoluminescence. The emission peaks of photoluminescence and mechanoluminescenc are the same at 488 nm, 610 nm and 648 nm, corresponding to the energy level transition of Pr³⁺ of ³H₄→³P₀, ³H₄→¹D₂ and ³F₂→³P₀, respectively. A slow-decaying mechanoluminescent behavior occurs when the continuous frictional stimulation and the mechanoluminescent intensity increase linearly with increasing the pressure. According to the thermoluminescent measurement, the slow-decaying mechanoluminescence is attributed to existence of deep traps. The deep traps provide an electron replenishment for shallow traps for Ca₂Ga₂GeO₇:Pr³⁺ under continuous stress stimulation. This paper may provide a material-and-experimental basis for the development and application of high-performance trap-controlled mechanoluminescent materials.

Rapid and non-invasive temperature detection inside biological tissues can be realized through a fluorescence intensity ratio thermometry technology, but it is still restricted due to the thermal quenching of fluorescence and the large absorption and scattering coefficients of tissues in practical applications. In this paper, cubic phase ScF₃:Yb³⁺/Er³⁺ nanocrystals with negative thermal expansion characteristics were synthesized by a one-step hydrothermal method, in which the thermal enhancement of up-conversion (UC) luminescence was achieved due to the thermally improved energy transfer efficiency from a shortened distance between the activator and sensitizer. For further realizing its application in biology, Nd³⁺ was introduced in ScF₃:Yb³⁺/Er³⁺ to construct a high-sensitivity temperature probe with near-infrared (NIR) excitation and NIR emission. Furthermore, calibrating the temperature measurement curve and designing the ex vivo experiment rationally can give a potential temperature detection of the present sample inside the tissue. The results indicate a strategy for solving the UC luminescence thermal quenching and developing NIR emission temperature probes for organisms.

Sulfur element doped RbNa₃(Li₁₂Si₄O_16-yS_y):Eu²⁺ narrow-band blue emitting UCr₄C₄ phosphors were synthesized by a conventional high-temperature solid-state method. The zero-thermal-quenching performance for the UCr₄C₄ structure was obtained, i.e., the integrated emission intensity at 250 ℃ increases to 107% rather than that at room temperature. The sites occupation of Eu²⁺ ions and defect analysis reveal the corresponding luminescence adjustment and zero-thermal-quenching mechanism. Also, the cationic substitution strategy of Ti⁴⁺ for Si⁴⁺ is designed to eliminate the shoulder band peak located at 525 nm for RbNa₃(Li₁₂Si₄O_16-yS_y):Eu²⁺ phosphors, and the color purity of blue emission is improved from 61.1% to 83.7%. It is indicated that the as-prepared RbNa₃(Li₁₂Si₃TiO_16-yS_y):Eu²⁺ phosphors could be used as a blue-emitting candidate material for liquid crystal display backlighting. This work can provide a guidance for the design of UCr₄C₄ phosphors to achieve the zero-thermal-quenching performance and high color purity.

A novel afterglow mechanoluminescent (ML) composite elastic material was obtained with ZrO₂:Ti⁴⁺ phosphor synthesized by a solid-state method and PDMS polymer. The structure, luminescence and traps properties of the phosphor and the elastomer were investigated by X-ray diffraction, scanning electron microscopy, and spectroscopy. The results show that ZrO₂ belongs to a monoclinic system with a space group P21/c (No.14), which is a centrosymmetric structure, and its ML is irrelevant to the common piezoluminescence. The band gap of the matrix is 5.01 eV, and its width is large, which is conducive to the irradiation transition of the luminescence energy level. The cyan photoluminescence and afterglow luminescence with Ti⁴⁺ characteristic emission e_g→t_2g are obtained after Ti⁴⁺ is uniformly doped into ZrO₂ as a luminescence center. After it is irradiated by 254 nm ultraviolet lamp, the composite elastic material prepared with ZrO₂:Ti⁴⁺ phosphor and PDMS can emit bright cyan ML under the stimulation of external forces such as tearing, pressing, bending and stretching. The ML occurs clearly for several seconds. The afterglow mechanoluminescent phenomenon is linearly dependent on the stress and it can repeat after irradiation, indicating a promising application potential in the fields of stress visualization, force-light sensing, engineering detection and artificial skin. In addition, a possible mechanism of afterglow ML caused by triboelectricity induced trapped carrier excitation was also proposed.

Sr₃Sn₂O₇:Sm³⁺ is a widely studied mechanoluminescent material, but there is still a lack of research on the doping amount of Sm³⁺. In this paper, Sr_3-xSn₂O₇: xSm³⁺ was prepared by a high-temperature solid-state method. A sample of Sr₃Sn₂O₇ with a small amount of Sm³⁺ still maintains a non-centrosymmetric double perovskite structure. The sample prepared has a stable photoluminescence, a long afterglow and mechanoluminescence after UV excitation or load application. The mechanoluminescence originates from the electron transition from the ⁴G_5/2 excited state of Sm³⁺ to the ⁶H_J (J=5/2, 7/2, 9/2) ground state. The luminescence performance was optimized by adjusting the value of x, and the optimum performance was achieved when x = 0.020. This study can provide a guidance for the future related research.

The mechanism of mechanoluminescent(ML) materials is a highly interdisciplinary research field involving the composite processes of mechanics, electricity, magnetism, and optics. At present, some special phenomena that cannot be fully covered by the existing mechanism models indicate that the process mechanism of ML is not fully clarified. This review represented the process mechanism of ML and the existing mechanism models and development strategies. In addition, some challenges and research directions of ML materials were also described.