Self-trapped exciton engineering for white-light emission in colloidal lead-free double perovskite nanocrystals

Intrinsic broadband photoluminescence (PL) of self-trapped excitons (STEs) are systematically studied in lead-free double perovskite nanocrystals (NCs). It is clarified that bandgap (direct/indirect) has important influence on the PL properties of STEs: indirect bandgap NCs exhibit strong exciton-phonon coupling which results in non-radiative STEs, while direct bandgap NCs exhibit moderate exciton-phonon coupling, inducing bright STE PL. Furthermore, by alloying K⁺ and Li⁺ ions in Cs₂AgInCl₆ NCs, the NCs exhibit broadband white-light emission. Charge-carrier dynamics study indicates that the efficient white-light emission originates from the further suppressed non-radiative processes of the STEs in the direct bandgap structure. This work may deepen the understanding of STEs and guide the design of high-performance lead-free perovskites.