Sb‐Doped Cs₃TbCl₆ Nanocrystals for Highly Efficient Narrow‐Band Green Emission and X‐Ray Imaging

Abstract Metal halide nanocrystals (NCs) with high photoluminescence quantum yield (PLQY) are desirable for lighting, display, and X‐ray detection. Herein, the novel lanthanide‐based halide NCs are committed to designing and optimizing the optical and scintillating properties, so as to unravel the PL origin, exciton dynamics, and optoelectronic applications. Sb‐doped zero‐dimensional (0D) Cs₃TbCl₆ NCs exhibit a green emission with a narrow full width of half maximum of 8.6 nm, and the best PLQY of 48.1% is about three times higher than that of undoped NCs. Experiments and theoretical calculations indicate that 0D crystalline and electronic structures make the exciton highly localized on [TbCl₆]³⁻ octahedron, which boosts the Cl⁻‐Tb³⁺ charge transfer process, thus resulting in bright Tb³⁺ emission. More importantly, the introduction of Sb³⁺ not only facilitates the photon absorption transition, but also builds an effective thermally boosting energy transfer channel assisted by [SbCl₆]³⁻‐induced self‐trapped state, which is responsible for the PL enhancement. The high luminescence efficiency and negligible self‐absorption of the Cs₃TbCl₆: Sb nanoscintillator enable a more sensitive X‐ray detection response compared with undoped sample. The study opens a new perspective to deeply understand the excited state dynamics of metal halide NCs, which helps to design high‐performance luminescent lanthanide‐based nanomaterials.