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 we propose a new mechanism for the formation of the defects in the anion sublattice associated with the Janh-Teller instability occurring near the cation impurities in the excited state. 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. 
Alexander Egranov and Tat'yana Sizova
cond-mat.mtrl-sci