Assembling Two Self‐Trapped Exciton Emissions in 0D Metal Halides with Near‐Unity Quantum Yield and Zero Thermal‐Quenching Photoluminescence

Abstract Zero‐dimensional (0D) lead‐free metal halides with efficient photoluminescence (PL) have wide application prospects in the optoelectronics field due to their unique structures and physicochemical properties. However, thermal quenching seriously hinders the practical applications of metal halide materials. Herein, this challenging effort is spearheaded to design novel lead‐free 0D indium‐based chloride K 3 InCl 6 :Sb 3+ single crystals with zero‐thermal quenching and a near‐unity PL quantum yield based on an effective strategy to suppress non‐radiative transitions. Experimental and computational studies indicate that the intense PL emission originates from self‐trapping excitons (STEs). The extremely low temperature of 7 K and time‐resolved spectra reveal the existence of two individual STEs emissions induced by the distinguished octahedrons in K 3 InCl 6 :Sb 3+ crystals. Meanwhile, the K 3 InCl 6 :Sb 3+ crystals can maintain PL stability without thermal quenching over a wide temperature range. Furthermore, the phosphor‐converted light‐emitting diodes can stably operate in the long term, benefitting from the significant structural and PL stability of Sb 3+ ‐doped 0D indium‐based chlorides. Therefore, this work not only presents new 0D metal halides with high efficiency and remarkable stability, but also provides insights into designing high‐performance optoelectronic materials.