Investigation of multiple centers in U3+:CaF2 single crystals

U3+:CaF2 single crystals with different dopant concentrations were grown in the presence or absence of PbF2 as oxygen scavenger by TGT. Multiple centers, at least including (Uca3+ - OF2-) and (Uca3d+- Fi-), were investigated by absorption spectra measured in the wavelength range of 190-2500 nm.Absorption coefficient ratios in different samples indicates that the concentration of (Uca3+ - OF2-) centers in U3+:CaF2 crystal grown with PbF2 was relatively low and almost remained constant. Without PbF2 as oxygen scavenger, (Uca3+ - OF2- centers with higher concentration are distinctly present in U3+ :CaF2 crystal. The oscillator strength of the transition 4I9/2 - > 4I15/2 of (Uca3+ - Fi-), corresponding to absorption band at 896 nm, is larger than that of (Uca3+ - OF2-) . Color centers in U3+:CaF2 were studied by gamma-irradiation and heat treating in oxygen atmosphere.