Saturation Effects in the Sensitized Fluorescence of CaF2(Ce, Mn)

The visible fluorescence of ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ impurities in crystals of Ca${\mathrm{F}}_2$ has been investigated under conditions of intense uv irradiation. A change in the fluorescent quantum efficiencies for both impurities is observed at high intensities. In particular, the resonant energy transfer from a ${\mathrm{Ce}}^{3+}$ sensitizer to a neighboring ${\mathrm{Mn}}^{2+}$ begins to saturate. A simple model is postulated to explain this effect. From this model an estimate can be made of the number of sensitizable sites surrounding the ${\mathrm{Ce}}^{3+}$. The rather large numbers obtained, about 150, may be due to some pairing of the ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ ions.