Configurational instability at the excited impurity ions in alkaline earth fluorites

The formation of intrinsic defects by ionizing radiation in some ionic crystals in the anion sublattice is only associated with the instability of the self-trapped exciton up to now. In this paper, on the basis of an analysis of experimental evidence already in the literature, we want to show that there are phenomena in the ionic crystals doped with some cations, which cannot be explained on the basis of existing models of the formation of radiation defects. A new mechanism for the formation of the defects in the anion sublattice associated with the Jahn–Teller instability occurring near the cation impurities in the excited state is proposed. The instability occurs when the degenerate excited state of the impurity ion is localized in the conduction band. We believe that the configuration interaction between the discrete impurity level and host continuum (effect Fano) plays an important role in this process. & 2012 Elsevier Ltd. All rights reserved.