Thallium-Doping-Modulated Photon Emission and Scintillation Performance in Cs₃Cu₂I₅ Nanocrystals

Fast and low-dose X-ray imaging is crucial for medical and security applications. Tl-doped Cs₃Cu₂I₅ stands out for dynamic X-ray imaging, outperforming many commercial scintillators. However, the mechanisms underlying the scintillation enhancements achieved through Tl doping remain unclear, hindering precise optimization and restricting utilization of its potential. Herein, the photon emission mechanism of Tl-doped Cs₃Cu₂I₅ nanocrystals was systematically investigated using photoluminescence, radioluminescence (RL), and femtosecond pump-probe laser spectroscopy, supported by time-dependent density functional theory calculations. The improved RL efficiency is attributed to the enhanced Jahn-Teller-type radiative recombination facilitated by the [TlI₈] polyhedrons. Moreover, the balanced electron-phonon coupling environment between the [Cu₂I₅] and [TlI₈] polyhedron effectively suppresses nonradiative recombination via intersection relaxation. This scintillator screen enables ghost-free X-ray imaging at a remarkable speed of 480 frames per second with a resolution of 30.4 line-pairs per millimeter, exceeding most reported scintillators. These findings offer advancing insights into developing dopant-triggered highly efficient scintillators.