Inorganic perovskite nanocrystals exhibit superior thermal stability and higher quantum yields compared to organic-inorganic hybrid perovskites. Additionally, perovskite nanocrystals have gained significant attention in fields such as solar cells, low-threshold lasers, light-emitting diodes (LEDs), and photodetectors, owing to their excellent tunable luminescent and optoelectronic properties. As a kind of nanocrystal with excellent photoelectric properties, CsPbX3 can achieve tunable emission in the whole visible spectral region by means of compositional alloying and quantum size effect. However, all-inorganic CsPbX3 perovskite nanocrystal still faces challenges in terms of poor stability and the toxicity of lead, which limits its application. Various strategies have been proposed to improve its resistance against environmental erosion, including surface modification, polymer encapsulation, and in-situ crystallization within inert glass matrices. Among them, embedding nanocrystals into inert glass matrices has been proposed to enhance their stability and demonstrate excellent heat resistance and resistance to intense light irradiation. However, traditional oxide glass is prepared under high-temperature open environments, leading to the volatilization of some glass components and the decomposition of perovskite nanocrystals. It results in unclear composition of the prepared glass and poor sample reproducibility. On the other hand, in response to the environmental toxicity of lead-based perovskites, non-toxic metals such as Sn, Bi, and Ge were employed for the substitution for Pb. Tin-based perovskites, in particular, have similar crystal and electronic structures to lead-based perovskites and exhibit fascinating near-infrared luminescence. By controlling the composition and quantum size, the emission spectra of CsSnX3 perovskites can be tuned from visible light to approximately 1 μm in the near-infrared spectral region, which can not be achieved in lead-based perovskite materials. However, due to the high sensitivity and easy oxidation of metastable Sn2+, the synthesis of CsSnX3 perovskite usually requires more stringent conditions, making the preparation procedure more difficult.Chalcogenide glassy flux method is introduced by using chalcogenide-based materials with good glass-forming ability, such as GeS2 and Sb2S3, as fluxes. Metal halides like CsX, SnX2, or PbX2 are dissolved in such chalcogenide fluxes, and the resulting mixture is melted and rapidly cooled to form glass. Subsequent heat treatment is applied to achieve controllable precipitation of the dissolved metal halides. This method allows for the formation of perovskite nanocrystals with arbitrary halide compositions within the transparent glass matrix, and meanwhile prevents the loss of metal halide precursors, therefore improving the reproducibility. The controllable crystallization mechanism of chalcogenide glass-ceramics with the composition of 79.2GeS2-15.8Sb2S3-5CsSnBr3 was investigated. The base samples were subjected to thermal treatments at 290 ℃ for 13, 20, 60 h, and 100 h. The variation of particle size and quantity of precipitated CsSnBr3 nanocrystals was observed by SEM and plotted as a function of the heat-treatment conditions. It was found that it exhibited power-law variations with time, following the Lifshitz-Slyozov-Wagner (LSW) theory. The phenomenon of increasing crystal size and decreasing crystal quantity during the heat treatment process was explained using Ostwald ripening theory. As the heat treatment progresses, the continuous growth of larger crystals consumes at the expense of smaller crystals.Eventually, when all crystal sizes became similar, this dissolution-growth behavior reach equilibrium.
Summary and prospects Inorganic perovskite nanocrystals have attracted significant attention due to their tunable emission wavelength and excellent optoelectronic properties. By utilizing glass flux method, controlled precipitation of perovskite nanocrystals such as CsPbX3 and CsSnX3 has been successfully achieved in sulfur-based glass. Tunable photoluminescence ranging from visible to near-infrared has been realized. The crystallization behavior of these perovskite nanocrystals in sulfur-based glass was revealed to follow the Ostwald ripening mechanism, allowing for controllability of nanocrystal size, crystal phase, and crystallinity. However, further research is required to investigate the characteristics of perovskite nanocrystals in sulfur-based glass, e.g., the relationship between their size, luminescence intensity, composition variations, and luminescence efficiency. Additionally, as a semiconductor material, sulfur-based glass holds potential application in electroluminescence compared to other substrate materials.