Multiple Self-Trapped Emissions in the Lead-Free Halide Cs₃Cu₂I₅

Low-dimensional copper halides with high luminance have attracted increasing interest as heavy-metal-free light emitters. However, the optical mechanisms underpinning their excellent luminescence remain underexplored. Here, we report multiple self-trapped emissions in Cs₃Cu₂I₅. Power-dependent photoluminescence spectra reveal the appearance of multiple self-trapped emission peaks with increasing excitation power, and this emission behavior is explored across a temperature range of 80-420 K. The zero-dimensional structure and soft crystal lattice contribute to the multiple self-trapped emissions in Cs₃Cu₂I₅: this explains the origin of the broad emission and the luminescence mechanism in Cs₃Cu₂I₅ and will assist in improving our understanding of the optical properties of other metal halides. We incorporate the Cs₃Cu₂I₅ in light-emitting diodes that achieve a peak luminance of 140 cd/m² and an external quantum efficiency of 0.27%.