Lone‐Pair‐Driven, Brightly Emitting Lead‐Free Zero‐Dimensional Inorganic Luminescent Member

Zero‐dimensional (0D) 5s2‐metal halide (MH) materials offer potential for use in solid‐state lighting, optical thermography, and scintillation applications. The organic components of most highly luminescent materials are inherently unstable under moisture and thermal stress, which restricts their practical use in advanced applications. Hence, highly luminescent and stable inorganic luminescent materials are required. In this work, to the best of current knowledge, a 0D completely inorganic luminescent member of K2SbCl5 that exhibits orange emission at 610 nm with an 80% photoluminescence quantum yield (PLQY) is reported for the first time. Density functional theory calculations reveal that the [SbCl5]2‐ square pyramidal units are the only optically active emission centers in K2SbCl5. The white light‐emitting device utilizing K2SbCl5 demonstrates impressive performance metrics, boasting a substantial color rendering index (CRI) of 94 and an exceptional luminous efficacy of 118.1 lm W−1. Hence, this isolated [SbCl5]2−square pyramidal environment serves as a design principle for the development of highly efficient inorganic Sb3+‐based luminescent materials for future optoelectronic applications. The zero‐dimensional (0D) compound K2SbCl5 boasts an extraordinary 80% photoluminescence quantum yield (PLQY), the highest reported among inorganic Sb3+–based metal halides (MH). Comprehensive research, employing cutting‐edge density functional calculations and spectroscopic analyses has revealed the origin of this remarkable PLQY and emission mechanism, offering valuable insights for developing efficient 0D MH materials for lighting.