Intrinsic Low‐Symmetry‐Assisted Growth and Efficient Luminescence in Zero‐Dimensional Hybrid Chloride Single Crystals

Abstract Zero‐dimensional (0D) organic–inorganic hybrid halides are emerging as promising lead‐free emissive materials. However, growing their high‐quality single crystals remains a formidable challenge, primarily due to uncontrolled nucleation and complex phase competition. Herein, a facile and eco‐friendly single‐heat‐source crystallization strategy is reported for the controllable growth of high‐quality MA 4 InCl 7 :Sb 3+ single crystals. The establishment of an axial temperature gradient promotes directional solute diffusion and Ostwald ripening, enabling spontaneous transformation from precursors to large transparent crystals. Structural analysis reveals that the asymmetric coordination environment and intrinsic low crystal symmetry facilitate selective nucleation and stable crystal growth. The grown transparent crystals exhibit intense yellow emission with a remarkable photoluminescence quantum yield (PLQY) of up to 92.86%, originating from self‐trapped excitons (STEs) within isolated [SbCl 6 ] 3− octahedra. The high optical quality and uniformity are further demonstrated by the fabrication of a bright yellow‐emitting LED, showing its potential in phototherapy‐related applications. This work not only provides a green and efficient pathway for synthesizing hybrid halide single crystals but also offers new insights into thermodynamics‐influenced selective crystallization associated with intrinsic low‐symmetry structural preferences.