PHOTOIONIZATION AND PHOTOCHEMICAL PRODUCTION OF COLOR-CENTERS IN CE3+-DOPED AND CE3+NA+-DOPED CAF2

The photoionization of Ce3+ in CaF2 has been reinvestigated with CaF2:Ce3+ and CaF2:Ce3+, Na+. Irradiation of the singly doped crystals with 308-nm light at room temperature produces Ce2+. However, at 80 K, we found no Ce2+ and observed only that the F- interstitial charge compensator moved from the (001) site to the (111) site. (Units are a/2, the unit cell dimension.) In the doubly doped crystals, we observed the production of Ce2+ at 80 K. Diffusion processes at higher temperatures lead to formation of other color centers. A mechanism that accounts for these observations is proposed.