Uranium speciation and its site occupancy in alkaline‐earth borophosphates

Alkaline‐earth (calcium, strontium, and barium) borophosphates doped with uranium (U) are prepared through conventional solid‐state reaction route. The form of stabilized uranium in these solid matrices was characterized and investigated using X‐ray diffraction (XRD), photo luminescence (PL) and extended X‐ray absorption fine structure (EXAFS). XRD measurements confirmed the single phase formation of uranium‐doped alkaline‐earth borophosphate samples. The PL characteristics of uranium in calcium and barium borophosphate are studied for the first time. Photoluminescence studies indicated presence of uranium as Uranyl in SrBPO5 and CaBPO5 matrices whereas in case of BaBPO5 the indication was for uranate species. The life time data corroborated the presence of a different uranium species in SrBPO5, CaBPO5, and BaBPO5. The site occupancy of uranium was further probed using EXAFS which confirmed that in case of BaBPO5, uranium enters the host as uranate whereas in case of SrBPO5 and CaBPO5, uranium enters as Uranyl.