The dielectric spectrum of erbium doped CaF₂

The complex dielectric constant has been measured at five audio frequencies (10 2 -10 4 Hz) over the temperature range 4.2-400K for eight concentrations (0.001-3.0 mol%) of erbium in calcium fluoride. Relaxation processes with activation energies of about 0.15, 0.4, 0.5 and 0.7 eV have been observed which correspond to previously reported dipolar complexes in rare-earth doped alkaline-earth fluorides. In addition, a previously unreported relaxation with an activation energy of approximately 0.028 eV has been found at low temperatures and high rare-earth concentrations. It is concluded that this relaxation is cluster-associated.