OPTICAL-SPECTRA AND PHOTOCONDUCTIVITY OF URANIUM-DOPED CAF2 CRYSTALS

Using infrared and optical absorption spectroscopy ill combination wit h photoconductivity measurements on uranium-doped calcium fluorite cry stals, we clarify a controversy in the assignment of U2+ and U4+ ion v alences in CaF2 crystals which exhibit different coloration. The energ y thresholds of donor-like processes (photoionization) follow the sequ ence of ionization potentials for uranium ions of different valences a nd indicate the green and yellow colors to be due to U4+ Of different charge compensation.