Transparent Organic Glass With Bright Triplet Excitons for High‐Spatial‐Resolution Indirect X‐Ray Imaging via Heavy Metal Halide Incorporation

Abstract Organic scintillators are emerging as promising candidates for indirect X‐ray imaging due to their tunable luminescent properties. However, achieving high transparency while maintaining a high content of organic luminescent material in organic scintillation pellets remains a challenge, which limits their imaging performance. In this study, a transparent luminescent organic glass based on ethyl‐triphenyl‐phosphonium chloride (ETPCl) is presented, which exhibits bright exciton emission and enhance X‐ray attenuation through the incorporation of lead halide. Remarkably, the addition of lead halide does not compromise the glass's high transparency, which remains ≈90% in the 400–800 nm wavelength range. Transient absorption measurements further reveal that the presence of heavy atoms enhances intersystem crossing and improves triplet emission efficiency, increasing the photoluminescence quantum yield from 7.1% in pure ETPCl glass to 35.4% in glass containing 10 mol.% PbCl 2 . Additionally, the heavy atom effect enhances X‐ray attenuation, leading to increased radioluminescence intensity. X‐ray imaging experiments demonstrate a spatial resolution of up to 19.9 lp mm⁻¹ at a modulation transfer function value of 0.2. These findings provide a promising approach for fabricating transparent organic scintillator glasses with improved triplet exciton utilization and X‐ray attenuation, enabling high‐resolution X‐ray imaging.