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 CsCu₂I₃ NCs exhibit broadband emission originating from self-trapped excitons (STEs), which arise from the 1D all-inorganic double chains composed of edge-sharing CuI₄ tetrahedra. While pressure‑induced STE emission enhancement has been demonstrated in bulk CsCu₂I₃ crystals, the high‑pressure behavior of CsCu₂I₃ 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 CsCu₂I₃ NCs. This enhancement is attributed to structural distortions occurring both within and between the CuI₄ tetrahedra under compression. In addition, the structural phase transitions (∼3.1 GPa) of CsCu₂I₃ 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 CsCu₂I₃ 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.