Achieving Near‐Unity Red Light Photoluminescence in Antimony Halide Crystals via Polyhedron Regulation

Exploration of efficient red emitting antimony hybrid halide with large Stokes shift and zero self‐absorption is highly desirable due to its enormous potential for applications in solid light emitting, and active optical waveguides. However, it is still challenging and rarely reported. Herein, a series of (TMS)2SbCl5 (TMS = triphenylsulfonium cation) crystals have been prepared with diverse [SbCl5]2‐ configurations and distinctive emission color. Among them, cubic‐phase (TMS)2SbCl5 shows bright red emission with photoluminescence quantum yield (PLQY) up to 90% and a large Stokes shift of 312 nm. In contrast, monoclinic and orthorhombic (TMS)2SbCl5 crystals deliver efficient yellow and orange emission, respectively. Comprehensive structural investigations reveal that larger Stokes shift and longer‐wavelength emission of cubic (TMS)2SbCl5 can be attributed to the larger lattice volume and longer Sb···Sb distance, which favor sufficient structural aberration freedom at excited states. Together with robust stability, (TMS)2SbCl5 crystal family has been applied as optical waveguide with ultralow loss coefficient of 3.67·10‐4 dB μm‐1, and shows superior performance in white‐light emission and anti‐counterfeiting. In short, our study provides a novel and fundamental perspective to structure‐property‐application relationship of antimony hybrid halides, which will contribute to future rational design of high‐performance emissive metal halides.