Colloidal Cu₄I₄ Clusters for High-Resolution X-ray Imaging Scintillation Screens

Luminescent copper halide clusters have attracted wide attention in light-emitting diodes and optical sensors due to their intriguing physicochemical properties and diverse chemical structures. Recently, the clusters have also been explored as promising scintillation materials due to the heavy copper halide cores that provide a large absorption cross section for X-ray radiation. However, the related research on copper halide cluster scintillators is only in its infancy, and the scintillation performance of the clusters still lags behind that of perovskite and its related metal halide structures. Here we report 0D cubane-like Cu₄I₄(L)₄ (L = 4-benzylpyridine or 4-tert-butylpyridine) clusters with broad emission band, high photoluminescence quantum yield (>85%), and a large Stokes shift. Density functional theory calculations demonstrate that the emission of both clusters mainly originates from the ligand-to-core charge transfer state. Besides, we successfully synthesized the colloidal cluster microcrystals and fabricated microcrystal-based films for X-ray imaging applications. We found that the cluster-based X-ray screens exhibited high light yields (>30000 photons MeV^-1), low detection limits (<150 nGy s^-1), and excellent spatial resolutions exceeding 20 lp mm^-1, surpassing the resolution of the most common commercial scintillators. We believe that this work provides the foundation for the further development of high-performance copper cluster-based scintillators.