Self‐Absorption‐Free Double Perovskite Scintillators for Synergistic Enhancement of Light Output and Spatial Resolution for X‐Ray and CBCT Imaging

ABSTRACT Lead halide perovskites have emerged as promising scintillators, yet their practical use in high‐resolution imaging is severely hampered by pronounced self‐absorption, which exerts distinct directional detriments: vertical self‐absorption causes severe scintillation light output attenuation, while lateral self‐absorption induces intense photon diffusion. This dual effect creates a trade‐off for classic direct bandgap perovskites like CsPbBr 3 : increasing thickness to boost x‐ray absorption inevitably exacerbates both vertical light loss and lateral resolution degradation. Herein, we report a lead‐free double perovskite Cs 2 NaTbCl 6 scintillator that fundamentally eliminates self‐absorption via a self‐trapped exciton‐mediated energy transfer to Tb 3+ luminescent centers. This design achieves an ultra‐large absorption‐emission shift, rendering the host fully transparent to its own emission and decoupling optical crosstalk in both directions. Breaking the conventional thickness‐resolution constraint, we realize a synergistic enhancement of light output and spatial resolution. Cs 2 NaTbCl 6 exhibits a high photoluminescence quantum yield and a substantially elevated steady‐state light yield; crucially, eliminating lateral self‐absorption‐induced photon diffusion enables a dramatic spatial resolution improvement. Experiments confirm Cs 2 NaTbCl 6 ’s superior performance in high‐fidelity x‐ray and cone‐beam computed tomography imaging, and more importantly, the design principle of eliminating directional self‐absorption effects via spectral decoupling provides a pivotal insight into the rational design of advanced scintillators for high‐resolution imaging.