Near‐Unity PLQY and Strong Broadband Emission From 0D (BYA) ₄ InCl ₇ Enabling High‐CRI Solid‐State Lighting

0D metal halides are promising light emitters owing to strong quantum confinement and efficient self-trapped exciton (STE) emission, yet achieving both broadband tunability and near-unity PLQY in lead-free systems remains challenging. This study reports the synthesis and comprehensive characterization of Sb³⁺-doped 0D perovskite single crystals, (BYA)₄InCl₇: xSb³⁺. Structural analysis confirms the successful substitution of Sb³⁺ into the isolated [InCl₆]³⁻ octahedra, which are spatially separated by bulky BYA⁺ organic cations, thereby preserving the intrinsic 0D framework. Sb³⁺ incorporation induces a substantial bandgap narrowing from 4.08 to 2.85 eV, accompanied by a pronounced enhancement of broadband STE emission. At an optimal doping level (x = 4.87%), the material achieves an ultrahigh PLQY of 97.53%. Temperature-dependent photoluminescence measurements, together with density functional theory calculations, reveal that the exceptional emission efficiency arises from strong electron phonon coupling and a low activation energy for thermal quenching. Furthermore, a prototype white light-emitting diode fabricated using the (BYA)₄InCl₇: Sb³⁺ phosphor exhibits excellent color rendition (CRI = 89.3) and robust operational stability. This study elucidates the structure property interplay governing Sb³⁺-doped 0D indium halides and highlights their promise as high-performance emitters for advanced optoelectronic devices.