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 ³P₁ to ¹S₀. Temperature-dependent photoluminescence (PL) shows a peak split at cryogenic temperature, which is ascribed to the Jahn-Teller effect of the ³P₁ 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.