Studies of the spin-Hamiltonian parameters and the Jahn-Teller distortions for tetragonal Cu(H(2)O)(6)(2+) clusters in trigonal A(2)Mg(3)(NO(3))(12).24H(2)O (A=La, Bi) crystals.

The anisotropic and isotropic spin-Hamiltonian parameters (g factors and hyperfine structure constants) of tetragonal Cu(H(2)O)(6)(2+) clusters due, respectively, to the static and dynamic Jahn-Teller effects for Cu(2+) in trigonal A(2)Mg(3)(NO(3))(12).24H(2)O (A=La, Bi) crystals are calculated from the high-order perturbation formulas based on the cluster approach. In the approach, the admixture between the d orbitals of 3d(n) ion and the p orbitals of ligand ion via covalence effect is considered. All of the calculated results are in agreement with the experimental values. The tetragonal elongations (characterized by DeltaR=R(parallel)-R( perpendicular)) of Cu(H(2)O)(6)(2+) cluster due to the Jahn-Teller effect in A(2)Mg(3)(NO(3))(12).24H(2)O crystals are acquired from the calculations. The results are discussed.

[Studies of the g factor and optical spectra for CaZrO3:Mn4+ crystal].

The complete high-order perturbation formula of g factor for 3d(3) ions in cubic octahedral site was derived. In the formula, both the contribution delta g(CF) to g-shift delta g (= g-g(s), where g(s) = 2.0023) due to crystal-field (CF) mechanism (related to the interactions of CF excited states with the ground state) and that (delta g(CT)) due to charge-transfer (CT) mechanism (related to the interactions of CT excited states with the ground state, which is omitted in crystal-field theory) are included. By using the formula and the parameters obtained from the optical spectra of CaZrO3:Mn4+ crystal, the g factor of CaZrO3:Mn4+ was calculated. The result is consistent with the experimental value. The calculations show that the contribution is opposite in sign and about 62% in magnitude compared with the contribution delta g(CF). It appears that both CF and CT mechanisms should be considered in the calculation of g factor for the high valence 3d(3) (e. g. , Mn4+ and Fe3+) ions in crystals.

Defect model and EPR parameters for the tetragonal Yb3+ center in KTaO3 crystal.

The defect model of the tetragonal Yb3+ (at K+ site) center in KTaO3 crystal is suggested, i.e., Yb3+ ion does not occupy the ideal K+ site, but is displaced by an amount DeltaZ along one of 100 axes because of the much smaller ionic radius of Yb3+ compared with that of the replaced K+. Based on the defect model, the EPR parameters (g factors g(parallel), g(perpendicular) and hyperfine structure constants 171A parallel, 171A perpendicular, 173A parallel, 173A perpendicular) are calculated by diagonalizing the 14 x 14 complete energy matrix. The calculated values are in agreement with the observed values and the off-center displacement DeltaZ (approximately 0.2 angstroms) is estimated from the calculations. These results are discussed.

[Investigation of optical and EPR spectra of ZnO : V3+ crystal].

In the present paper, the 45 X 45 energy matrix of the 3d2 ions in trigonal symmetry with the strong-field-coupling mechanism is established. The forty-five optical energy levels and five EPR parameters (including the zero-field splitting D, g factors g//, g perpendicular and hyperfine structure constants A//, A perpendicular) of ZnO : V3+ cryst are calculated from the diagonalization of this complete energy matrix. The calculated results are in agreement with the observed values. Based on the calculation, it was found that the local structure of V3+ impurity center is different from the corresponding structure in the host crystal, i. e., the V3+ ion in ZnO does not occupy the exact Zn2+ site, but is displaced by DeltaZ approximately 0.003 nm along the c3 axis. The reasonableness of these results is discussed.

Defect models of the three trigonal Ti3+ centers in LiF:Ti3+ and LiF:Ti3+:Mg2+ crystals.

The EPR g factors of the trigonal Ti3+ center A in LiF:Ti3+ and two additional trigonal Ti3+ centers B and C in LiF:Ti3+:Mg2+ crystals are calculated from the third-order perturbation formulas based on the cluster approach. From the calculations and by considering the Ti3+ displacement along 111 axis obtained by ENDOR experiment, the defect models for the three Ti3+ centers are suggested. For center A, there are two possible models: (i) [Ti3+F3-O3(2-)] cluster and (ii) [Ti3+F6-] cluster with the Ti3+ off-center caused by a neighboring Li+ vacancy (VLi+) at <111> axis. The latter seems the more likely. The defect models of centers B and C are the [Ti3+F3-O(3)2-] clusters associated with a neighboring: Mg2+ ion at the Li+ site along 111 axis in the vicinity of three F- ions and three O2- ions, respectively. The reasonableness of these models is discussed.