Homo- and Heterovalent Doping-Mediated Self-Trapped Exciton Emission and Energy Transfer in Mn-Doped Cs₂Na_1–<i>x</i>Ag_<i>x</i>BiCl₆ Double Perovskites

Abstract

Double perovskites exhibit low toxicity, intrinsic thermodynamic stability, and small carrier effective mass. Herein, a novel doping route was adopted to incorporate Mn ions into Cs₂Na_1-<i>x</i>Ag_<i>x</i>BiCl₆ double perovskites for engineering the band gap and tailoring the energy transfer. The as-prepared Cs₂Na_1-<i>x</i>Ag_<i>x</i>BiCl₆ (0 < <i>x</i> < 1) exhibited excellent photoluminescence and a broad self-trapped exciton (STE) band from 500 to 900 nm, which exhibited an abnormal emission peak blue shift with increasing temperature. For Mn-doped Cs₂Na_1-<i>x</i>Ag_<i>x</i>BiCl₆, the two photoluminescence (PL) bands from d-d transition emission of Mn ions and STEs were always observed simultaneously in the PL window. The distinct energy-transfer channel from the Mn²⁺ ion guest to the double-perovskite host resulted in the dominant Mn²⁺ emission. Our results will be helpful for further understanding the nature of the photophysics of double perovskites.