Self-Trapped Exciton Emission In An Sn(Ii)-Doped All-Inorganic Zero-Dimensional Zinc Halide Perovskite Variant

The toxicity of Pb in conventional perovskites impedes the commercialization of their optoelectronic devices. Therefore, the search for comparable Pb-free perovskites is vital and needs urgent attention. Herein, for the first time, we successfully synthesize the Sn(ii)-doped Pb-free zinc-based perovskite variant Cs2ZnCl4. The influence of doping is investigated both experimentally and theoretically. Broad bright red emission with a large Stokes shift is observed and attributed to the self-trapped exciton (STE) emission of the doped disphenoidal [SnCl4](2-) units in the host matrix, from P-3(1) to S-1(0). Temperature-dependent photoluminescence (PL) shows a peak split at cryogenic temperature, which is ascribed to the Jahn-Teller effect of the P-3(1) state. Theoretical study reveals that the impurity states of Sn2+ shrink the bandgap and localize the band edges, and distortion of [SnCl4](2-) under excitation ultimately leads to the STE emission. This work is significant for STE emission studies and will pave a way for Pb-free perovskite variants in illumination applications.