Theoretical studies of the spin Hamiltonian parameters and the local structures for M2+ (M=Co, Mn, V and Ni) ions in CsMgCl3.

The spin Hamiltonian parameters (zero-field splitting D, g factors g parallel, g perpendicular and hyperfine structure constants A parallel, A perpendicular) for M2+ (M=Co, Mn, V and Ni) ions in CsMgCl3 are studied by using the perturbation formulas of the spin Hamiltonian parameters for 3dn (n=7, 5, 3, 8) ions in trigonal symmetry based on the cluster approach. In these formulas, the contributions to the spin Hamiltonian parameters from the admixture of d orbitals of the central ions with the p orbitals of the ligands and from the trigonal distortion are included and the parameters related to these effects can be obtained from the optical spectra and the local structures of the studied systems. Based on the studies, it is found that the local trigonal distortion angle beta in the M2+ impurity center is unlike that betaH (approximately 51.71 degrees) in the host CsMgCl3. The spin Hamiltonian parameters for these divalent ions in CsMgCl3 are also satisfactorily explained by using the local angle beta. The validity of the results is discussed.

Theoretical studies of the local structure for the trigonal Ti(3+) center in LiF crystal.

The local structure of the trigonal Ti(3+) center in LiF crystal is theoretically investigated by using the perturbation formulas of the anisotropic g factors and g(//) and g(/_) for a 3d(1) ion in trigonally distorted octahedra based on the cluster approach. From the studies on the basis of various possible structure models, the local structure of the trigonal Ti(3+) center may be characterized as [TiF(3)O(3)](6-) cluster (or model I). In this model, the impurity Ti(3+) is expected to substitute for the host Li(+) ion and shift away from its regular lattice site along the [111] (or C(3)) axis by about 0.19 A due to the strong electrostatic attraction of the O(2-) triangle replacing the original F(-) triangle. The magnitude of the above displacement obtained in this work is comparable with that ( approximately 0.2-0.3A) given by ENDOR experiment. Moreover, the cubic field parameter Dq (approximately 1497 cm(-1)) based on the above structure model is also in agreement with that (approximately 1500 cm(-1)) obtained from the experimental optical spectra of the studied system. The theoretical investigations of the local structure in this work may be useful to understand optical properties of Ti-doped LiF.