Calcium fluoride crystals doped with ErF3 and PbF2 have been grown using the vertical Bridgman method. Temperature and frequency dependence of the complex dielectric constant have been measured at seven audio frequencies (1-100kHz) over the temperature range of 150-300 K. The activation energy for dipole reorientation and the relaxation time constant, To, has been determined from the observed relaxation processes. The effect of Er3+, Pb2+ ions and the X-ray irradiation on the optical and dielectric spectra was studied. A comparison of our results with those obtained by other authors is also given. (c) 2007 Elsevier B.V. All rights reserved.