Dipole orientation effects in rare-earth doped CdF2

A number of experiences carried out by means of ITC technique in the temperature range 80-200K shows unequivocally that n.n. Rare Earth-Fluorine Insterstitial (RE-FI) dipole reorientation occurs in CdF2: Eu, resolving the puzzle of the lack of this kind of relaxation in trivalent ions doped CdF2. The activation energy for orientation (epsilon = 0,40 eV) and the preexponential factor (Tauo = 10-12 s) are evaluated for the principal ITC peak (T(sub) M = 152.5K) discussed and compared with the analogous parameters in Eu doped Ca and Sr fluorides. Other ITC peaks at 168 and 186 K are also analyzed. A parallel study on CdF2: Gd shows that eletronic effects are not negligible and can mask dispolar relaxations. The difference between Eu and Gd is discussed