Lead-free rare-earth double perovskite Cs2AgIn1−γ−xBixLaγCl6 nanocrystals with highly efficient warm-white emission

Lead-free double perovskite nanocrystals (NCs), such as Cs2AgInCl6, have attracted considerable attention as stable and non-toxic alternatives to lead-based perovskites. However, the low photoluminescence (PL) intensity of pristine Cs2AgInCl6 limits its practical applications. In this study, a series of Cs2AgIn1−γ−xBixLaγCl6 NCs were synthesized to break the parity-forbidden transition and modify the associated optical functionalities. A broadband bright warm-white emission in the visible region was achieved, with an excellent PL quantum yield of 60%. The dynamic mechanism, involving ultrafast transient absorption, suggests that high-efficiency PL is induced by triplet self-trapping exciton emission. The incorporation of La3+-Bi3+ facilitated the singlet-triplet transition by increasing the lifetime and quickening the intersystem crossing process. This finding provides a reliable method for optimizing the optical properties of emerging lead-free halide perovskite NCs.