Irradiation effects in CaF2 probed by Raman scattering

The formation conditions and dynamics of Ca colloids and point defects that appear in irradiated single crystals of CaF2 were investigated by Raman spectroscopy. The intensity changes in the Raman spectra because of the presence of different concentrations of point defects and Ca colloids that emerged in CaF2 after irradiation with 2.2GeV Au ions were used to study their distribution and stability under illumination with three laser wavelengths (473, 532 and 633nm) at different output powers (2 to 200mW). A damage saturation at a fluence of 6x10(11) ioncm(-2) was observed. The dependence of the spectral changes on the ion fluence can be described by a core/halo damage cross-section model. A radius of 13-18nm was obtained for the outer (halo) cylinder, in agreement with previous swelling studies. Illuminations of irradiated samples with blue (473nm) and green (532nm) lasers were found to be extremely efficient in bleaching the samples, while illumination with a red (633nm) laser did not lead to a sample recovery. This indicates that the bleaching process is governed by recombination of point defects that have to overcome an energy barrier. Typical time constants for the processes involved are presented. Copyright (c) 2016 John Wiley & Sons, Ltd.