Decoupling X‐Ray Absorption and Emission: Ionic TADF Scintillators With Heavy‐Atom‐Functionalized Organic Anions

ABSTRACT Organic scintillators hold great promise for x‐ray imaging due to their solution processability and low cost, yet their practical application is fundamentally limited by weak x‐ray absorption and inefficient exciton utilization. Here, we overcome these limitations through a functional‐separation design that yields exceptional radioluminescence in a purely organic system. We have developed ionic phosphonium scintillators integrating thermally activated delayed fluorescence (TADF) cations with heavy‐atom‐containing organic anions. In this architecture, the organic anions act as sensitizing antennas for x‐ray photons, while the TADF cations independently govern the emission process. Upon x‐ray excitation, energy is unidirectionally transferred from the heavy anions to the luminophores, followed by efficient triplet harvesting via TADF—delivering materials that achieve photoluminescence quantum yields of up to 81%. Leveraging this molecular design, a highly doped (60 wt%) transparent screen based on the brominated compound achieves a remarkable spatial resolution of 97.8 lp/mm. The imaging screen enables clear visualization of fine structures, such as the internal wiring in electronic chips and a 400‐mesh copper grid. By decoupling x‐ray absorption from emission, our work establishes a new paradigm for designing solution‐processable organic scintillators with high radioluminescence performance, offering a promising pathway toward advanced x‐ray imaging applications.