Origin of singlet self-trapped exciton and enhancement of photoluminescence quantum yield of organic–inorganic hybrid antimony(III) chlorides with the [SbCl₅]²⁻ units

Sb-based organic–inorganic hybrid metal halides (OIHMHs) with [SbCl₅]²⁻ units have been widely reported due to high photoluminescence quantum yield (PLQY) and occasional multiple self-trapped exciton (STE) emission bands mainly out of singlet and triplet states, and their multi-band emission is important in white light-emitting diode (WLED). However, not all these OIHMH compounds can produce both emissions out of singlet STE and triplet STE at room temperature simultaneously. It is crucial to consider how the singlet STE generates and retains to emit light at room temperature for this material’s design and application. Herein, a strategy is proposed that can significantly lift Sb halide PLQY by synthesizing two Sb-based OIHMHs using organic amine cations of different-sized and -quantity, which modulate the distance of neighboring emission centers. Therein, the occurrence of singlet STE emission is found to be closely related to the distance of [SbCl₅]²⁻ units and local unit distortion in the lattice. The larger distance can produce smaller local distortions, favoring the formation of the singlet STE emission band at higher energy. This is the first work to reveal the relationship between the local structure and the origin of the singlet STE emission band, providing new insights into the modulation of the Sb-based OIHMH’s emission.