Efficient White Light‐Emitting Diodes Based on Cu(I) Activated Single‐Phase Halide Single Crystals

Abstract

Single‐phase white light emitters have become a potential substitute for tricolor phosphor mixtures for the white light‐emitting diodes (WLEDs) application to simplify device structure and eliminate self‐absorption. Newly developed low‐dimensional halides, noted for their highly efficient luminescent characteristics, have seen increasing interest in recent years. Herein, highly efficient white‐light emission is demonstrated in single‐phase zero‐dimensional halide single crystal, namely monovalent Cu‐doped Cs2HfCl6. Cs2HfCl6:Cu single crystals have three luminescent centers. Two emission peaks at 365 nm and 380 nm correspond to the intrinsic self‐trapped excitons emission and a defect‐related trapped exciton emission, respectively. Cu doping introduces an intense Cu‐bound exciton emission peaking at 540 nm with a large Stokes shift of 250 nm and a high photoluminescence quantum yield of 68%. With different excitation wavelengths and Cu‐doping concentrations, Cs2HfCl6:Cu single crystals show tunable emissions. Under 254 nm ultraviolet light excitation, Cs2HfCl6:0.5%Cu yields cold white light with a high color rendering index (Ra = 87.3). These findings demonstrate the potential of Cs2HfCl6:Cu as a promising phosphor for cold WLEDs.