One-Dimensional Cs ₅ Cu ₃ Cl ₄ Br ₂ I ₂ Crystal with Efficient and Thermally Stable Cyan Photoluminescence

In recent years, copper-based halides have attracted considerable attention due to their exceptional optical properties. Nevertheless, these materials often exhibit poor thermal stability at elevated temperatures, which significantly limits their potential for practical applications. In this study, we successfully synthesized large-sized, one-dimensional chain-structured Cs5Cu3Cl4Br2I2 single crystals using the vertical Bridgman method. The crystal’s structure and composition were characterized through XRD and TG-DTA. Our experimental investigations into the optical properties of the Cs5Cu3Cl4Br2I2 single crystals revealed strong cyan emission with a high photoluminescence quantum yield (PLQY) of approximately 90.78% and a significant Stokes shift, attributable to self-trapped exciton (STE) emission. Additionally, we measured the temperature-dependent fluorescence spectra to further elucidate the luminescence mechanism. Notably, the fluorescence intensity of the Cs5Cu3Cl4Br2I2 single crystal increased with temperature, peaking at 425 K, a phenomenon seldom observed in copper-based halides. This study underscores the potential of Cs5Cu3Cl4Br2I2 single crystals for high-temperature optoelectronic applications.