Investigation of the structure of impurity defects in alkali halide crystals by the method of fluorescence EXAFS

It has been shown by experiment that the structure of impurity centers in NaCl–Sr crystals depends on impurity concentration and storage time of crystals. At low concentration and in quenched crystals the impurity is in site of the lattice. At concentrations higher than 0.15 wt% Sr, the impurity forms SrCl2 phase. For the crystals containing Cu+ impurity, it has been shown that an increase in the impurity concentration leads to the formation of clusters with CuCl structure. At the same time the existence of isolated copper ions shifted from the sites of the lattice is obvious. This leads to asymmetry of the environment of copper, which is manifested both in the absorption spectra in the ultraviolet region and in the EXAFS spectra.Heating of the crystals leads to destruction of complex clusters and formation exclusively of centers containing isolated copper ions.