Impact of bismuth-doping on enhanced radiative recombination in lead-free double-perovskite nanocrystals

Lead-free double-perovskite nanocrystals (NCs) have received considerable attention as promising candidates for environmentally friendly optical applications. Furthermore, double-perovskite nanostructures are known to be physically stable compared to most other inorganic halide perovskites, with a generic chemical formula of ABX₃ (e.g., A = Cs⁺; B = Sn²⁺ or Ge²⁺; X = Cl^-, Br^-, I^-, or their combination). However, relevant experimental studies on the photophysical properties are still insufficient for Pb-free double-perovskite NCs. Herein, we synthesized Cs₂Ag_0.65Na_0.35InCl₆ NCs doped with bismuth (Bi³⁺) ions and investigated their photophysical properties to reveal the role of the dopant on the enhanced photoemission properties. Specifically, it was found that the photoluminescence quantum yield (PLQY) increased up to 33.2% by 2% Bi-doping. The optical bandgap of the NCs decreased from 3.47 eV to 3.41 eV as the amount of the dopant increased from 2% to 15%. To find out the effect of Bi-doping, the temperature-dependent PL properties of the undoped and doped NCs were investigated by utilizing steady-state and time-resolved PL spectroscopy. With increasing the temperature from 20 K to 300 K, the PL intensities of the doped NCs decreased slower than the undoped ones. The correlated average PL lifetimes of both the bismuth-doped and undoped NCs decreased with increasing the temperature. The experimental results revealed that all the NC samples showed thermal quenching with the temperature increasing, and the PL quenching was suppressed in bismuth-doped NCs.