Ratiometric Copper Iodide Scintillators for Temperature‐Resolved X‐Ray Imaging

ABSTRACT Multifunctional X‐ray imaging that simultaneously resolves structural and thermal information is highly desirable under thermally dynamic and extreme conditions. Yet conventional systems require separate temperature sensors, which increases complexity and limits direct spatial correlation between the two. Here, we report a structurally engineered copper iodide (Cu–I) cluster scintillator that integrates high‐resolution x‐ray imaging with ratiometric thermometry in a single material. Regulating the Cu–I cluster and ligand coordination environment yields dual‐emissive Cu 4 I 4 (3F‐py) 4 , which exhibits two well‐resolved excited‐state emissions and a high light yield of 40 000 photons MeV −1 . The two channels respond differently to temperature, producing a pronounced intensity‐ratio change and continuous radioluminescence color evolution from orange to blue as the temperature decreases from 300 to 100 K. Excited‐state analysis reveals that the electron‐withdrawing substituent stabilizes ligand‐centered frontier orbitals and lowers the barrier for interconversion from the cluster‐centered state to the metal/halide‐to‐ligand charge‐transfer state, enabling broad‐range thermochromism. The resulting scintillation screen achieves a spatial resolution exceeding 13 lp mm −1 , while the Boltzmann‐type temperature dependence of the emission ratio allows quantitative thermal information to be encoded directly into the spectral ratio and color of x‐ray images. This work establishes excited‐state engineering of cluster scintillators as a strategy for temperature‐resolved x‐ray imaging.