Color centers in the ionized and in the triplet state —Z 2 centers in ytterbium-doped KCl crystals

Z₂ centers in Yb²⁺-doped KCl crystals are investigated by optical absorption experiments and by ESR experiments using the optically excited triplet state. Two mainZ₂ center configurations have been found. One of them shows (100) axial symmetry and is optically orientable in the crystal. The other one possesses (110) symmetry elements. The measured fine structure constants are explained partly by dipole-dipole interaction of the two electronic magnetic moments partly by spin orbit interaction due to the Ytterbium impurity. The structure of the optical absorption spectra is attributed to as²–s d charge transfer transition affected by the combined effect of crystal field and spin orbit interaction.