Solid state speciation of uranium and its local structure in SrCeO using photoluminescence spectroscopy.

An effort was taken to carry our speciation study of uranium ion in technologically important cerate host SrCeO using time resolved photoluminescence spectroscopy. Such studies are not relevant only to nuclear industry but can give rich insight into fundamentals of 5f electron chemistry in solid state systems. In this work both undoped and varied amount of uranium doped SrCeO compound is synthesized using complex polymerization method and is characterized systematically using X-ray diffraction (XRD), Raman spectroscopy, impedance spectroscopy and scanning electron microscopy (SEM). Both XRD and Raman spectroscopy confirmed the formation of pure SrCeO which has tendency to decompose peritectically to SrCeO and SrO at higher temperature. Uranium doping is confirmed by XRD. Uranium exhibits a rich chemistry owing to its variable oxidation state from +3 to +6. Each of them exhibits distinct luminescence properties either due to f-f transitions or ligand to metal charge transfer (LMCT). We have taken SrCeO as a model host lattice to understand the photophysical characteristics of uranium ion in it. Emission spectroscopy revealed the stabilization of uranium as U (VI) in the form of UO (octahedral uranate) in SrCeO. Emission kinetics study reflects that uranate ions are not homogeneously distributed in SrCeO and it has two different environments due to its stabilization at both Sr as well as Ce site. The lifetime population analysis interestingly pinpointed that majority of uranate ion resided at Ce site. The critical energy-transfer distance between the uranate ion was determined based on which the concentration quenching mechanism was attributed to electric multipolar interaction. These studies are very important in designing SrCeO based optoelectronic material as well exploring it for actinides studies.