Extended x-ray-absorption fine-structure study ofY3+andSr2+impurities in CaF2

The extended x-ray-absorption fine-structure technique has been used to measure lattice relaxation around ${\mathrm{Sr}}^{2+}$ and ${\mathrm{Y}}^{3+}$ impurities in a Ca${\mathrm{F}}_2$ host. In both cases the impurity near-neighbor anion bond length is much closer to that in the respective compound (Sr${\mathrm{F}}_2$ and Y${\mathrm{F}}_3$) than that of Ca${\mathrm{F}}_2$. Radial distribution curves for 1 and 6 mol% Y:Ca${\mathrm{F}}_2$ suggest no change in the ${\mathrm{Y}}^{3+}$ near-neighbor environment for concentrations $c$, $0.01\le c\le 0.06$, and therefore lend no support to proposed defect-cluster models for Y:Ca${\mathrm{F}}_2$.