Studies of the EPR parameters g(i) and A(i) for Co2+ in the octahedral sites of Y3Al5O12 and Y3Ga5O12 crystals

The perturbation formulas of EPR g factors g(\\) g(perpendicular to) and hy perfine structure constants A(\\) A(perpendicular to) for the trigonal octa hedral 3d(7) cluster are derived considering not only the configuration int eraction effect due to the admixture among ground and excited states, but a lso the covalency effect due to the admixture between the d electrons of th e 3d(7) ion and the p electrons of ligands. In these formulas, the paramete rs related to both effects and the trigonal field parameters are estimated from the optical spectra and the structural parameters of the studied syste m. According to these formulas, the EPR parameters g(\\), g(perpendicular t o), A(\\) and A(perpendicular to) for Co2+ in the octahedral sites of Y3Al5 O12 and Y3Ga5O12 garnets are satisfactorily explained from the optical spec tra and the structure data. The role of the covalency effect is discussed.