Fluorinated Copper(I) Iodine Cluster Scintillators Enable High-Temperature X-ray Imaging

The development of scintillators that maintain excellent performance under high temperatures is a critical challenge. Here, by simply replacing the triphenylphosphine ligand with its fluorinated analogue, we successfully switched the emission pathway of Cu2I2 clusters from pure phosphorescence to a hybrid phosphorescence/thermally activated delayed fluorescence (TADF) mechanism, enabling adaptive high-temperature X-ray imaging. Combined experimental and theoretical investigations reveal that the fluorination strategy reduces the singlet–triplet energy gap to an exceptionally small value of 35 meV, thereby promoting efficient reverse intersystem crossing. The TADF contribution reaches 95.7% at room temperature. This temperature-responsive characteristic endows the fluorinated cluster with adaptive X-ray imaging capability across a broad temperature window from 293 to 413 K, overcoming the thermal quenching phenomenon in traditional phosphorescence-only scintillators. This work establishes a molecular design approach for smart scintillators capable of reliable operation in demanding thermal environments.