Observation of optically stimulated reorientation of dipolar defects in Pr³⁺-doped strontium fluoride

We have performed optical and dielectric measurements on the reorientation of C_4ν(F^-) dipolar defects found in SrF₂ doped with Pr³⁺. By monitoring the polarization of fluorescence from optically excited Pr³⁺ ions in these defect sites, we have observed the movement of the adjacent interstitial F^-. We have also observed the motion of these F^- ions by measuring the thermally stimulated depolarization current. These two procedures yield significantly different results. We propose an optically driven mechanism for interstitial F^- motion that may explain this disparity.