PRECIPITATION OF DOPANT IONS IN NACL-EU+2 CRYSTALS

The aim of the work presented was to study the effect of the annealing temperature upon the formation of second phases in the NaCl matrix by using the optical absorption and ionic thermocurrent measurements. Th e 60, 125, 235 and 350 degrees C isotherms were followed mainly for cr ystals containing 120 mole ppm of divalent europium. The three lower a nnealing temperatures result in a decay of the impurity-vacancy dipole concentration up to similar to 5% of the initial value being accompan ied by the growth of metastable phases with their characteristic optic al absorption spectra previously observed for as received samples, onl y. At 350 degrees C the decay of the impurity-vacancy dipole concentra tion reaches similar to 20% of the initial value, and the newly appear ed optical absorption spectrum has been ascribed to the stable EuCl2 p recipitates with the PbCl2 type of structure. (C) 1998 Elsevier Scienc e B.V. All rights reserved.