Unlocking the Core Geometry of High-Efficiency Copper Iodide Cluster Scintillators

Copper(I) halide-based emitters have recently garnered significant attention for their potential in X-ray imaging applications owing to their efficient emission, facile synthesis, and low toxicity. While several strategies have been proposed to improve scintillation efficiency in these systems, the critical role of Cu-I cores─particularly during ultrafast energy conversion and transport─has received limited attention. In this work, we introduce a unified ligand strategy to construct a series of zero-dimensional copper(I) iodide clusters, including a Cu₁I₁ monomer, Cu₂I₂ rhomboid dimer, and Cu₄I₄ cubane tetramer, all exhibiting near-unity photoluminescence quantum yield (ϕ_PL). This approach enables a systematic investigation of how the core architecture governs radioluminescence (RL) behavior and efficiency beyond ϕ_PL. Our results demonstrate that the core geometry has a strong influence on both thermal stability and exciton relaxation pathways. Notably, low-temperature PL-RL differences uncover a previously unrecognized exciton relaxation channel intrinsic to the cubane cluster, allowing a fraction of excitons to directly populate the ³CC state. This process confines exciton generation, transport, and radiative recombination within the Cu-I cubane, thereby potentially increasing the exciton transfer efficiency and enhancing scintillation efficiency. These findings provide critical insights into the fundamental scintillation mechanisms and structure-property relationships of Cu-I clusters, establishing core geometry as a key design principle for the development of next-generation, high-performance scintillators.