Enhancement of self-trapped excitons and near-infrared emission in Bi3+/Er3+ co-doped Cs2Ag0.4Na0.6InCl6 double perovskite

Abstract

Erbium (Er) complexes are used as optical gain materials for signal generation in the telecom C-band at 1540 nm, but they need a sensitizer to enhance absorption. Na⁺ substitution for Ag⁺ and Bi³⁺ doping at the In³⁺ site is a possible strategy to enhance the broadband emission of Cs₂AgInCl₆, which could be used as a sensitizer for energy transfer to rare-earth elements. Herein, self-trapped exciton (STE) energy transfer to Er³⁺ at 1540 nm in double perovskite is reported. An acid precipitation method was used to synthesize Cs₂AgInCl₆ and its derivatives with Er³⁺, Bi³⁺, and Na⁺. Bare Cs₂AgInCl₆:Er emission signals were found to be weak at 1540 nm, but Bi³⁺ doping increased them by 12 times, and Bi³⁺ and Na⁺ doping increased signal intensity by up to 25 times. Electron paramagnetic resonance spectroscopy characterized a decrease in axial symmetry over the Er³⁺ ions after the substitutions of Na⁺ and Bi³⁺ in Cs₂AgInCl₆ at low temperatures (<7 K) for the first time. Moreover, an increase in pressure compressed the structure, which tuned the STE transition for free exciton emission, and a further increase in pressure distorted the cubic phase above 70 kbar.