“Charge transfer–lattice” clusters induced by charged impurities

A new type of self-consistent charge transfer–lattice states induced by charged impurities in their vicinity in ionic–covalent matrices are proposed and considered. A theory of these states is based on a charge transfer vibronic exciton (CTVE) model. The CTVE model explains the laser excitation-induced conversion of the sites accompanied by memory effect both caused by Eu3+ impurities in BaFCl crystal. The origin of this phenomenon connects with cross-relaxation between CTVE trapped by impurity, and excited states of this impurity. The CTVE model allows to propose a general mechanism of multi-site structure appearance induced by charged impurities in ionic–covalent solids. This mechanism is considered as an example of multi-site structure caused by RE3+ impurities in LiNbO3 crystal.