Spectroscopic techniques to investigate aggregation and precipitation of cation impurities in alkali halides: application to impurity hardening and irradiation sensitivity

The clustering and precipitation of cation impurities in alkali halides is discussed and techniques for their investigation are reviewed. Non-spectroscopic techniques such as dielectric relaxation, X-ray diffraction, optical and electron microscopy, are summarized, together with the results obtained using them. The main body of the review is given over, however, to a more detailed consideration of optical absorption, luminescence, Raman and paramagnetic resonance spectroscopy. New results obtained by means of these techniques on monovalent and divalent cation doped systems are presented. The usefulness of the techniques is illustrated by specific attention to the correlation between impurity aggregation/precipitation and two phenomena, mechanical hardening and F-centre production under irradiation. (UK)