Dielectric Relaxation Changes Due to Optical Conversion "FZ1" in KCl:SrCl2Crystals

Abstract
Optical-absorption and dielectric-loss measurements have been carried out and correlated in additively colored KCl:SrCl2 single crystals, in order to discern whether the impurity-vacancy dipolar complexes are involved in the optical conversion of F centers to Z1 centers. The Z1 centers were created by irradiating samples containing only F centers at 40°C by means of high-intensity light absorbed by the F band; a concentration of 1017 Z1 centers was obtained in about 30 sec. In the meantime the concentration of impurity-vacancy complexes nIV was measured by means of dielectric losses. The results show that nIV is not instantaneously affected by the growth of Z1 centers but rather decreases slowly thereafter in a time of about 20 min after the F-light illumination. The total change of nIV was approximately 10% of the initial value (1018 dipole cm3), i.e., 1017 dipoles. Similar measurements have been carried out by irradiating at 0°C and by determining nIV by measuring the discharge of the induced polarization at increasing temperature (method of the ionic thermoconductivity): the results obtained thus are consistent with the ones at 40°C. This experiment rules out the possibility that the impurity-vacancy dipoles take part directly in the Z1-center formation; the proposed models are discussed in view of these results.

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