  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.
