Dipolar Complexes in Calcium Fluoride Doped with Erbium

The rotation of Er³⁺-Fᵢ^_^- dipoles in CaF₂ was studied by the ionic thermocurrent (ITC) technique. Relaxation peaks at 138 K ($E=0.380$ eV, τ₀=2×10^-13 sec) and 54 K ($E=0.167$ eV, τ₀=3×10^-15 sec) were observed, and it is proposed that these are produced by the reorientation of the tetragonal complex (nearest-neighbor interstitial fluorine) and the trigonal complex (next-nearest-neighbor interstitial fluorine), respectively. Twidell recently reported inducing movement of the interstitial fluorine with uv light and his results are compared with the effects on the ITC spectrum caused by uv and by electron irradiation at low temperature.