Scintillation Efficiency Enhancement of Cs 3 Cu 2 I 5 Single Crystals via Exciton Harvesting Toward Low‐Dose and High‐Resolution X‐Ray Imaging

ABSTRACT Low‐dimensional metal halides, especially Cu‐based systems, have emerged as promising x‐ray scintillators due to high scintillation efficiency. However, mitigating non‐radiative energy losses remains a critical hurdle to achieving further performance gains. In this work, efficient exciton utilization was achieved in Bridgman‐grown Cs 3 Cu 2 I 5 single crystals by introducing Mn 2 + to modulate exciton relaxation dynamics. The synergistic effect of efficient Mn 2+ ‐centered emission and the energy transfer from STE to Mn 2 + and Mn 2+ ‐Mn 2+ pairs effectively suppresses non‐radiative dissipation, achieving a remarkable light yield of 120 000 photons MeV −1 under x‐ray irradiation. Thanks to ultrabright scintillation yield, the Cs 3 Cu 2 I 5 :Mn single crystals demonstrate a superior spatial resolution of 30 lp mm −1 and a low detection threshold of 91 nGy s −1 , enabling clear resolution of fine features in a 50 µm copper grid. This study clarifies the exciton‐dopant interactions in Mn 2+ ‐activated Cs 3 Cu 2 I 5 scintillators and provides guidance for designing efficient materials for x‐ray imaging.