Defects and self-trapped exciton regulation in rare-earth doped all-inorganic perovskites

Abstract

All-inorganic lead halide perovskites (CsPbX₃) have attracted extensive attention due to their excellent optical and photovoltaic properties and have been applied to various novel optoelectronic devices. Transition metal ion doping has proven to be a practical pathway for improving their performance and extending their future application. However, it has not been realized how metal ions with different doping concentrations quantitatively affect the band structure, induce the formation of defect states and self-trapped excitons, and ultimately reflect the controllability of the optical properties of perovskites. Herein, single-crystalline erbium-doped CsPbCl_3xBr_3(1−x) perovskites were grown using a temperature-controlled chemical vapor deposition (CVD) method. By precisely controlling the growth temperature and concentration of doped transition metal ions, their emitted photoluminescence (PL) can be broadly tuned from the red (1.82 eV) to near-infrared (NIR) band (1.53 eV) while maintaining their intrinsic bandgap without significant variation. Through micro-area PL and time-resolved PL (TRPL) experiments, we found that when the doped transition metal ion concentration gradually increased in a pretty narrow range, such as from 0.87% to 1.02%, new luminescence centers gradually appeared, including defect luminescence and self-trapped exciton luminescence. Combined with density functional theory (DFT) calculations, the microscopic mechanism of transition metal ion doping inducing the above properties was quantitatively analyzed. The regulation method here is universal and may be applied to the future material design of multi-color and even white light-emitting devices.