White-light defect emission and enhanced photoluminescence efficiency in a 0D indium-based metal halide

Abstract

Low-dimensional ns²-metal halide compounds with confined structures and localized electronic states have received considerable attention due to their superior luminescence properties, while the intriguing photophysical dynamics of metal halides without ns² electrons is still elusive and has yet to be investigated. Herein, we have developed a novel In³⁺-based (C₆H₈N)₆InBr₉ single crystal that exhibits intrinsic white-light emission at room temperature. Such white light stems from multiple defect states owing to the presence of Br vacancies, which however delivers a low photoluminescence quantum yield (PLQY) (2.72%) due to a severe thermal quenching effect. To improve the photoluminescence efficiency, the Sb³⁺ ion with a 5s² lone pair has been embedded into the lattice, which leads to broadband orange emission with a high PLQY of up to 71.84%. The enhanced PL efficiency results from efficient triplet self-trapped excitons (STEs) in the (SbBr₆)³⁻ octahedron and the energy transfer from defect states to STE states. This work not only sheds light on the mechanism of defect-related white-light emission, but provides a successful strategy for designing novel materials with excellent PL properties for versatile optical applications.