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The EPR g factors gparallel, gperpendicular and the hyperfine structure constants Aparallel, Aperpendicular for two trigonal Co2+ centers (i.e. Co2+(I) center at the substitutional site and Co2+(II) center at the interstitial site) in Al2O3 crystals are calculated from the second-order perturbation formulas based on the cluster approach. In these formulas, the contributions to EPR parameters from both the spin-orbit coupling parameter of central 3dn ion and that of ligand are included. The calculated results are in reasonable agreement with the observed values. Based on the calculations, the defect structures of both Co2+ centers in Al2O3 crystals are obtained and the negative sign of Aparallel for Co2+(I) center is suggested. The results are discussed.

The EPR zero-field splittings D of Mn2+ and Fe3+ ions in anatase crystals at room and low temperatures are calculated from the high-order perturbation formula of zero-field splitting D for 3d(5) ions in tetragonal symmetry based on the dominant spin-orbit coupling mechanism. The calculated results are consistent with the observed values. From the calculations, Mn2+ and Fe3+ ions are suggested to substitute for T-i(4+) ions in anatase (in the previous paper, Mn2+ ion was Suggested at an interstitial site rather than substitutional site) and the defect structures (characterized mainly by the local oxygen parameter mu) for both tetragonal Mn2+ and Fe3+ impurity centers are estimated. The different zero-field splitting at room and low temperatures are due mainly to the change of local oxygen parameter mu with the temperature. These results are discussed. (C) 2007 Elsevier B.V. All rights reserved.

The trigonal field parameters v and v' of magnetic semiconductor NaCrS2 are calculated from the superposition model, and its g factors g(parallel to) and g(perpendicular to) are calculated from the high-order perturbation formulas of 3d(3) ions in trigonal symmetry obtained by the one and two spin-orbit coupling parameter models. These calculations are based on the structural data of NaCrS2 crystal. The calculated results suggest that the superposition model is effective to the analyses of the low-symmetry field parameters of 3d(n) ions in crystals and that the two spin-orbit coupling parameter model (where the contributions from both the spin-orbit coupling parameter of 3d(n) ion and that of ligand are considered) is preferable to the one spin-orbit coupling parameter model (in which the contribution from only the spin-orbit coupling parameter of 3d(n) ion is considered) in the explanations of g factors in the cases that ligands have large spin-orbit coupling parameter in 3d(n) clusters. (c) 2006 Elsevier B.V. All rights reserved.

The complete high-order perturbation formula of g factor, including not only the widely used crystal-field (CF) mechanism, but also the neglected change-transfer (CT) mechanism in the CF theory, is established for a 3d(8) ion in cubic octahedral site. From the formula, the g-shifts Delta g (=g - gs, where gs approximate to 2.0023, the value of free electron) of Ni2+ ion in CsMgX3 (X = Cl, Br, I) crystals are calculated. The results suggest that the g-shift Delta gCT due to the CT mechanism and the Delta gCF due to CF mechanism have the same sign and the importance of Delta gCT follows the order: CsMgI3: Ni2+ > CsMgBr3: Ni2+ > CsMgCl3: Ni2+. So, in the calculations of g or Delta g of 3d(n) MXm clusters in crystals, the contributions to g factor from both the CT and CF mechanisms should be taken into account in the case of heavy-element ligand ions, such as Br- and I- ions. (c) 2005 Elsevier B.V. All rights reserved.

In this paper, we calculate the optical spectra data (crystal-field energy levels), the electron paramagnetic resonance (EPR) g factors g(parallel to), g(perpendicular to) of Yb3+ and hyperfine structure constants A(parallel to), A(perpendicular to) of Yb-171(3+) and Yb-173(3+) isotopes in CaWO4 crystal in a unified way from the crystal-field theory. All the calculated results are in good agreement with the experimental values. The signs of A(parallel to) and A(perpendicular to) for both isotopes Yb-171(3+) and Yb-173(3+) are suggested. (C) 2004 Elsevier B.V. All rights reserved.