Stereochemical Activity and Luminescence Mechanism in (CHN)SnCl Doped with ns Metal Ions.

Metal halide luminescent materials, particularly those doped with ns ions, exhibit exceptional optical properties. However, the luminescent mechanisms associated with the stereochemical activity of lone-pair electrons remain insufficiently explored. In this study, zero-dimensional (0D) tin-based halide (CHN)SnCl is utilized as a model system to investigate the effects of lattice distortion and lone-pair electron expression on fluorescence emission characteristics by doping with 6s and 5s ions. The findings reveal that compared to 6s ions, 5s ion doping results in stronger electron-phonon coupling, causing significant octahedral lattice distortion and producing unique dual emissions along with a large Stokes shift of 317 nm. Remarkably, even at temperatures as high as 360 K, (CHN)SnCl:Sb maintains its dual emission due to insufficient thermal activation energy to promote electron transition from excited state 1 to excited state 2. In contrast, 6s doping exhibits a single blue emission with a small Stokes shift of 101 nm. Additionally, calculations of the electron localization function reveal that 5s lone pairs exhibit static stereochemical expression with specific spatial orientation, while 6s lone pairs display dynamic behavior. These findings highlight the critical role of lone-pair stereochemistry in governing the photophysical properties of ns-doped metal halides, offering new insights into their luminescent mechanisms.