Charge Conversion of Irradiated Rare-Earth Ions in CaF2. II. Thermoluminescent Spectra

Abstract

High-resolution emission spectra are observed for individual glow peaks from all the lanthanide ions in Ca${\mathrm{F}}_2$. The crystals are irradiated with x rays (or $\gamma$ rays) at 77° and subsequently heated. For a given ion, identical spectra are observed for all glow peaks below 300°K. In all cases where the spectra can be interpreted, the ions responsible for these glow peaks are in sites of cubic symmetry. For some of these ions this is the first time that cubic emission has been seen without the complication of accompanying emission from sites of lower symmetry. The emission above room temperature is always from ions of axial symmetry, which for ${\mathrm{Gd}}^{3+}$ has been identified as tetragonal. Comparison is also made between ${\mathrm{Gd}}^{3+}$ in Ca${\mathrm{F}}_2$, Sr${\mathrm{F}}_2$, and Ba${\mathrm{F}}_2$. In the last two cases both cubic and trigonal symmetry are observed below room temperature.