Photoionization and photochemical production of color centers in Ce3+- and Ce3+:Na+-doped CaF2

Abstract

The photoionization of ${\mathrm{Ce}}^{3+}$ in ${\mathrm{CaF}}_2$ has been reinvestigated with ${\mathrm{CaF}}_2$:${\mathrm{Ce}}^{3+}$ and ${\mathrm{CaF}}_2$:${\mathrm{Ce}}^{3+}$, ${\mathrm{Na}}^{+}$. Irradiation of the singly doped crystals with 308-nm light at room temperature produces ${\mathrm{Ce}}^{2+}$. However, at 80 K, we found no ${\mathrm{Ce}}^{2+}$ and observed only that the ${\mathit{F}}^{\mathrm{-}}$ 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 ${\mathrm{Ce}}^{2+}$ at 80 K. Diffusion processes at higher temperatures lead to formation of other color centers. A mechanism that accounts for these observations is proposed.