Boosting Scintillation Yield in Cs ₃ Cu ₂ I ₅ Single Crystals via Europium (II) Incorporation toward High‐Resolution and Fast X‐Ray Imaging

Abstract Low‐dimensional halides (LDHs), in particular Cu(I)‐based halides, are attracting great attention due to their non‐toxic nature and efficient radioluminescence. Nonetheless, these LDHs still suffer serious scintillation yield loss due to nonradiative exciton‐exciton/exciton‐defect interactions, which poses a significant challenge for X‐ray imaging applications. Herein, an exciton‐harvesting strategy is proposed to enhance the scintillation yield of 0D Cs 3 Cu 2 I 5 single crystals by Eu 2+ doping. It is demonstrated that the 5d‐4f transitions and charge transfer process of Eu 2+ in the Cs 3 Cu 2 I 5 host can mitigate nonradiative energy dissipation effectively, possessing a high scintillation performance. Additionally, based on their X‐ray excited radioluminescence properties, the Cs 3 Cu 2 I 5 :Eu 2+ single crystals achieve high‐resolution and fast X‐ray imaging, resolving fine structures in a 300‐mesh copper grid (≈50 µm) and clearly capturing dynamic profiles of a chopper blade operating at 180 Hz. This advancement establishes a novel design strategy for developing highly efficient scintillators toward high‐resolution and fast X‐ray imaging applications.