Clustering and defect structure of CaF2crystals doped with YbF3and ErF3as determined byF19nuclear magnetic resonance

Abstract

${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ NMR studies of single crystals of Ca${\mathrm{F}}_2$ doped with 2, 1, and 0.5 mole percent of both Er${\mathrm{F}}_3$ and Yb${\mathrm{F}}_3$ have been carried out at room temperature. In Er${\mathrm{F}}_3$-doped crystals, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ resonances have been identified for lattice fluorides having both one and two ${\mathrm{Er}}^{3+}$ ions in nearest-neighbor cation sites and for an interstitial fluoride with two ${\mathrm{Er}}^{3+}$ ions in nearest-neighbor sites. In Yb${\mathrm{F}}_3$-doped crystals, resonances have also been identified for lattice fluorides having both one and two ${\mathrm{Yb}}^{3+}$ ions in nearest-neighbor cation sites plus a fluoride with two nearby ${\mathrm{Yb}}^{3+}$ ions not in normal cation sites. Analysis of the results indicate that all the rare-earth ions are associated in some type of cluster at all concentrations studied and that the structure of these clusters does not agree with any model proposed in the literature. Comparison of these results with an earlier study of doped Cd${\mathrm{F}}_2$ crystals shows that the same dopant produces a greater distortion of the cubic fluoride ion lattice in Ca${\mathrm{F}}_2$ than in Cd${\mathrm{F}}_2$.