Synthesis of Thermally Stable and Highly Luminescent Cs 5 Cu 3 Cl 6 I 2 Nanocrystals with Nonlinear Optical Response.

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs 5 Cu 3 Cl 6 I 2 , which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs 5 Cu 3 Cl 6 I 2 nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs 5 Cu 3 Cl 6 I 2 NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating-cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs 5 Cu 3 Cl 6 I 2 NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs 5 Cu 3 Cl 6 I 2 NCs and a foundation for further research.