Pressure Regulating Self‐Trapped Exciton Emission Enhancement of One‐Dimensional Cu‐Based Halide Nanocrystals

Copper(I)‐based halide nanocrystals (NCs) have captured significant attention as a viable alternative to lead halides in various light‐emitting applications, owing to their low toxicity, cost‐effectiveness, and abundance. Among these materials, the all‐inorganic one‐dimensional (1D) halide CsCu 2 I 3 NCs exhibit broadband emission originating from self‐trapped excitons (STEs), which arise from the 1D all‐inorganic double chains composed of edge‐sharing CuI 4 tetrahedra. While pressure‑induced STE emission enhancement has been demonstrated in bulk CsCu 2 I 3 crystals, the high‑pressure behavior of CsCu 2 I 3 NCs—particularly the role of nanoscale dimensions on the phase transition pressure and emission properties—remains unexplored. In this study, by employing a high‐pressure technique, we have successfully achieved a significant enhancement in the emission of STEs within Copper(I)‐based halide CsCu 2 I 3 NCs. This enhancement is attributed to structural distortions occurring both within and between the CuI 4 tetrahedra under compression. In addition, the structural phase transitions (∼3.1 GPa) of CsCu 2 I 3 NCs from orthorhombic (I2/M) phase to the triclinic (P1̅) phase under pressure were the rooted reason for the change of optical properties. This reduction in transition pressure compared to bulk CsCu 2 I 3 crystals (∼5 GPa) is attributed to a size effect in nanomaterials. Our research provided further evidence between structure and optical properties in tetrahedron‐based halide complexes.