Photoinduced anisotropy in absorption band of M+A -color center for SrCl2-K crystal

This paper presents the absorption spectra in the 400-800 nm range of SrCl2-K crystal after its exposure to ionizing radiation at a temperature of 150 K. Based on the literature data, it has been indicated that the absorption bands of 444 nm, 535 nm and 760 nm are conditioned by -color centers. In this crystal the -center is a system of two anion vacancies (near the impurity cation K+) that captures one electron.

The studies have shown that an intensive illumination in the absorption bands of 444 nm, 535 nm destroys -center, while the absorption band of 760 nm is not optically active. It has been found that when the specimens are illuminated by linearly polarized light in one absorption band (optically active), the anisotropy (dichroism) occurs not only in this band but also in other bands. It is even true for the 760-nm band, in which, under the direct illumination, photoinduced optical anisotropy is not observed.

It has been demonstrated that the illumination of -color center by polarized light with the electric vector E || [100] in the short-wave (444 nm) absorption band causes the optical anisotropy (dichroism) not only in this band, but also in two other bands: 535 nm and 760 nm. In this case, in an absorption band of 535 nm, the anisotropy is of the same sign as for the absorption band of 444 nm, while in the absorption band of 760 nm the anisotropy of the opposite sign arises and it is greater in absolute magnitude. However, if the illumination was carried out by polarized light with E || [110] at a maximum of the 444 nm band, then the anisotropy of the opposite sign occurs in the absorption band of 535 nm, but in the long-wave band of 760 nm the anisotropy was absent.

The results of optical illumination by linearly polarized light in the 535 nm band are quite similar to the results of illumination by linearly polarized light in the 444-nm band.

Using the dipole model of the color center and (previously suggested) “Methods for calculating the correlation of the parameters of photoinduced optical anisotropy of cubic crystals”, the work presents theoretical calculations of such relations for cubic crystals with -color centers. The results of theoretical calculations are qualitatively consistent with the experimental results. This testifies the correctness of the developed methods of calculating the relations of parameters of photoinduced optical anisotropy of cubic crystals in different absorption bands of identical anisotropic color centers. Therefore, the suggested methods can be used when considering dipole models of other color centers.

Keywords: colour centres, dichroism, dipole model, anisotropy.