Boosting Energy Transfer from Self-Trapped Exciton to Er3+ Through Sb3+ Doping in Cs2Na(Lu/Er)Cl6 Double Perovskites

Metal halide double perovskites are highly attractive for optoelectronic applications because of their superior optical properties. Here, a novel halide double perovskite, Cs2NaLuCl6, exhibiting bright blue emission originating from the host self-trapped exciton (STE) is reported. Through doping with Sb3+, the dopant-induced STE is formed in the crystals with a photoluminescence quantum yield up to 94%. The energy transfer from the dopant STE to Er3+ is superior to the direct excitation of Er3+, which is more efficient than the energy transfer from the host STE to Er3+. Furthermore, the energy transfer efficiency from STE to Er3+ is boosted from 8% to 33% through Sb3+ doping in Cs2NaLu0.95Er0.05Cl6. Due to the strong electron-phonon coupling and efficient energy transfer, the as-prepared crystals exhibit intense dual-band emissions and remarkable thermal stability. Importantly, the STE emission variation after the Er3+-substitution is explored based on the electron-phonon coupling effect. These findings provide new insights into the excited state dynamics of halide double perovskites and extend their luminescence applications such as white light-emitting diodes and night vision.