Enhancement of self-trapped excitons and near-infrared emission in Bi/Er co-doped CsAgNaInCl double perovskite.

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 Bi doping at the In site is a possible strategy to enhance the broadband emission of CsAgInCl, which could be used as a sensitizer for energy transfer to rare-earth elements. Herein, self-trapped exciton (STE) energy transfer to Er at 1540 nm in double perovskite is reported. An acid precipitation method was used to synthesize CsAgInCl and its derivatives with Er, Bi, and Na. Bare CsAgInCl:Er emission signals were found to be weak at 1540 nm, but Bi doping increased them by 12 times, and Bi and Na doping increased signal intensity by up to 25 times. Electron paramagnetic resonance spectroscopy characterized a decrease in axial symmetry over the Er ions after the substitutions of Na and Bi in CsAgInCl 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.