Abstract
Uranium is the heaviest naturally occurring element with appreciable crustal abundance. Its dominated oxidation state under oxidizing conditions is UVI, and this cation is typically found within the uranyl cation, UO22+. The combination of high atomic number and high oxidation state gives rise to both high X‐ray attenuation efficiency and intense green luminescence originating from ligand‐to‐metal charge transfer. These two features suggest that UVI materials might act as superior X‐ray scintillators, but this postulate has remained substantially untested. Here we report the first observation of intense X‐ray scintillation in a uranyl‐organic framework (SCU‐9) that is observable by the naked eye. This compound exhibits the highest quantum yield of uranyl‐organic frameworks reported. Combining the advantage in minimizing the non‐radiative relaxation during the X‐ray excitation process over those of inorganic salts of uranium, SCU‐9 exhibits a very efficient X‐ray to green light luminescence conversion. The luminescence intensity of SCU‐9 shows an essentially linear correlation with the received X‐ray intensity, and is comparable with that of commercially‐available CsI:Tl. More importantly, SCU‐9 possesses an improved X‐ray attenuation efficiency (E > 20 keV) as well as enhanced radiation resistance and decreased hygroscopy, when compared to CsI:Tl.