Structural Relaxation Modulated Phonon‐Assisted Energy Transfer Scintillator for Simultaneous X‐Ray Imaging and Thermal Signals Visualization

ABSTRACT Abnormal overheating often leads to malfunctions in electronic components during operation. Although traditional scintillators have shown great potential in object imaging, they are often unable to capture thermal signals. In this work, a series of Tb 3+ /Eu 3+ co‐doped MOF‐based scintillators ( Tb x Eu (1–x) ) were developed with exceptional Förster resonance energy transfer from Tb 3+ to Eu 3+ . Crucially, a distinctive structural relaxation occurs at 440 K in Tb x Eu (1–x) , which activates a specific phonon mode to dissipate the excess energy from Tb 3+ ( 5 D 4 ) to Eu 3+ ( 5 D 1 ). The abrupt weakening of coordination interaction and subsequent lattice softening above 440 K trigger the release of vibrational freedom and the increase of phonon population, leading to pronounced energy transfer efficiency enhancement and temperature‐dependent luminescent color shift. Leveraging the unique high‐temperature responsiveness and superior scintillation performance of Tb 0.99 Eu 0.01 , the developed Tb 0.99 Eu 0.01 ‐screen enables simultaneous capture of x‐ray imaging and thermal signals, which provides a new approach for achieving precise structural observation of electronic components and spatial localization of the abnormal overheating zone.