Elucidating the Role of Antimony Dopant in Optical Properties of Brightly Luminescent Zero-Dimensional Organic–Inorganic Metal Halides

Doping strategies are regarded as an effective means to improve the optical properties of organic–inorganic metal halides and have attracted widespread attention. Here, we synthesized undoped and Sb3+-doped MA4InX7 (X = Cl, Br; MA+ = CH3NH3+) single crystals. Sb3+-doped samples exhibited bright broadband emissions of extrinsic self-trapped excitons (STEs). The photoluminescence quantum yields of Sb3+-doped MA4InX7 (X = Cl, Br) are increased by more than 38 and 15 times compared with undoped samples, respectively. While a similar behavior in the optical characteristics was observed before and after introducing Sb3+, explained well by the non-ignorable trace Sb3+ ions in the precursors, which often confused researchers’ judgement about the origin of photoluminescence (PL) emission in previous studies. In addition, an apparent concentration quenching effect was found when excessive dopants were fed. The close connection between extrinsic STE emissions and the vibrational mode of [SbX6]3– octahedrons was revealed by temperature-dependent PL spectra and Raman spectra. Our work provides a deep understanding of extrinsic STE emission and thus facilitates the design and development of eco-friendly light-emitting metal halides.