Cr3+ doped Cs2ZnCl4 microcrystals enabling near-infrared emission

As a promising lead-free metal halide, Cs2ZnCl4 has the potential to serve as a host for achieving various photoluminescence emissions with different colors through ion doping. Therefore, studying the optical properties of various ions doped into Cs2ZnCl4 with tetrahedron coordination is of great significance. However, there is still a lack of research on near-infrared (NIR) emission in Cs2ZnCl4. In this study, we successfully synthesized Cs2ZnCl4:Cr3+ crystals using a simple hydrothermal method. The Cs2ZnCl4:Cr3+ exhibits luminescence in the range of 800–1300 nm, with a peak position at 915 nm and a full width at half maximum (FWHM) of 150 nm under 375 nm excitation. Through the analysis of photoluminescence spectra, density functional theory (DFT), lifetime decay curves, temperature-dependent spectra, and time-resolved photoluminescence (TRPL), we confirmed the presence of two potential sites for Cr3+ ion occupancy. Additionally, NIR phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by combining Cs2ZnCl4:Cr3+ with a green LED chip. The night-vision camera captured the distribution of blood vessels and bones in the fingers, demonstrating the promising potential of this material in the field of NIR imaging.