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

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.