Sb-Doped Cs₃ TbCl₆ Nanocrystals for Highly Efficient Narrow-Band Green Emission and X-Ray Imaging

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) Cs₃ TbCl₆ 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 Cs₃ TbCl₆ : 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.