Enhanced X-ray and β-ray Scintillation in a Bismuth MOF through Europium Doping

Metal-organic frameworks (MOFs) have recently emerged as promising scintillation platforms owing to their highly tunable architectures, versatile photophysical properties, and ability to incorporate high-Z elements and luminescent centers into a single lattice. In this study, we present a Bi-based MOF, Bi-ndc, along with its Eu-doped derivative, Eu@Bi-ndc, and provide a comparison of their scintillation characteristics. Bi-ndc, constructed from high-Z Bi³⁺ metal nodes and π-conjugated naphthalenedicarboxylate organic linkers, exhibits ligand-centered radioluminescence but suffers from inefficient utilization of triplet excitons. The doping of Eu³⁺ into the framework activates an antenna-type sensitization pathway in which linker triplet states transfer energy to Eu³⁺, thereby enabling effective harvesting of both singlet and triplet excitons. Consequently, Eu@Bi-ndc displays enhanced X-ray-excited luminescence, achieving a detection limit of 6.36 μGy s^-1, which is 111-fold lower than that of Bi-ndc. Beyond X-ray detection, Eu@Bi-ndc represents the second MOF material to exhibit a measurable β-ray scintillation spectrum and the second example of a lanthanide-based MOF β-ray scintillator. Under β-ray irradiation from a ⁹⁰Sr-⁹⁰Y source, Eu@Bi-ndc exhibits distinct Eu³⁺ emission signatures, outperforming Bi-ndc in terms of scintillation efficiency. This work underscores the critical role of lanthanide doping in enhancing the scintillation performance of MOF-based materials.