Site-selective spectroscopy of CaF2:Ho3+

Abstract

Using selective laser excitation, the crystallographic sites arising from fluoride compensation of ${\mathrm{Ho}}^{3+}$ doped into Ca${\mathrm{F}}_2$ have been investigated. Two sites are found corresponding to single-${\mathrm{Ho}}^{3+}$ -single-fluoride-interstitial pairs. These sites are suspected to be the tetragonal and trigonal sites observed in the similar Ca${\mathrm{F}}_2$: ${\mathrm{Er}}^{3+}$ system. Two sites and a family of similar sites are found to be dimers and/or higher-order clusters. These sites exhibit upconversion and energy-transfer-assisted decay characteristics of the closely coupled rare-earth ions. This phenomenon was used to observe energy transfer between an ${\mathrm{Er}}^{3+}$ and a ${\mathrm{Ho}}^{3+}$ in a double-doped crystal, and therefore show the equivalency of the respective sites in each of the ion's individual spectra.