Wen-Lin Feng

Spin-Hamiltonian parameters of Yb3+ ions in trigonally-distorted octahedral sites of Na3Sc2V3O12 garnet

The spin-Hamiltonian (SH) parameters (g factors, g ¶ and g ⊥, and hyperfine structure constants, 171 A ¶, 171 A ⊥, 173 A ¶ and 173 A ⊥) for Yb3+ ions in trigonally-distorted octahedral sites of Na3Sc2V3O12 garnet were calculated from a complete diagonalization (of energy matrix) method (CDM) concerning 4f13 ions in trigonal symmetry. In the method, the Zeeman and hyperfine interaction terms are added to the Hamiltonian in the conventional CDM and the crystal-field parameters are estimated from the empirical superposition model. From the calculations, these SH parameters are explained reasonably. The defect structure of Yb3+ impurity centres in Na3Sc2V3O12 garnet and the signs of 171 Ai (i = ¶ or ⊥) and 173 Ai are also suggested. The intrinsic parameters in the superposition model obtained in the studied system show that > > . This point is consistent with the intrinsic parameters obtained for many rare earth ion systems and can be regarded as suitable.

Studies of the optical spectral bands and spin-Hamiltonian parameters for Ni2+ ions in a CdCl2 crystal

The eight optical spectral bands and three spin-Hamiltonian parameters (g factors g //, g ⊥ and zero-field splitting |D|) of Ni2+ ion in CdCl2 crystal are calculated from the method of diagonalizing the complete energy matrix of 3d8 ions in trigonal symmetry. In the method, the contributions to spin-Hamiltonian parameters from both the spin-orbit coupling parameter of the central 3d n ion, and that of the ligand, are included. The calculated results are consistent with the experimental values. The defect structure of the trigonal Ni2+ impurity center in CdCl2 are acquired from the calculations. The results are discussed.

Substitutional site and defect structure of Ni2+ in LiNbO3 crystal studied from the optical and electron paramagnetic resonance spectra

The energy levels (which are related to optical spectra) and effective spin-Hamiltonian parameters (g factors g //, g ⊥ and zero-field splitting D which are measured by electron paramagnetic resonance (EPR) spectra) of Ni2+ ion in LiNbO3 are calculated from the complete diagonalization (of energy matrix) method. In the calculations, the Ni2+ ion is suggested to replace Li+ ion with the local relaxation in LiNbO3. This point is in disagreement with the opinions in many previous papers in which the substitutional site and structural data of Ni2+ at Nb5+ site are used to explain the experimental data obtained by the optical and EPR spectra. The present calculated results are also consistent with the experimental values. The reasonableness of the substitutional site and defect structure of Ni2+ at Li+ site is discussed.

Investigations of the optical spectra and EPR g-factors for the tetragonal Ce3+centers in YPO4 and LuPO4 crystals

The optical spectral band positions and EPR g-factors (g‖ , g ⊥) for the tetragonal Ce3+ centers in YPO4 and LuPO4 crystals with the zircon-structure are calculated using a complete diagonalization (of the energy matrix) method (CDM) related to 4f1 ions in tetragonal symmetry. In this method, the Zeeman interaction term are added to the Hamiltonian in the conventional CDM and so no perturbation calculations are required to obtain the g factors. The crystal-field parameters used in the calculations are obtained from the superposition model in which the local lattice relaxation related to the bonding lengths is considered. The calculated results are in reasonable agreement with the experimental values. It is found that the four observed optical bands for both the systems can be attributed to Ce3+ ions in a tetragonal crystal field.

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 the Local Geometry and EPR Parameters of V3+ and Cr4+ Centers in Al2O3 Crystals

The EPR parameters (zero-field splitting D and g factors g||, g⊥) of 3d2 V3+ and Cr4+ centers in Al2O3 crystals are calculated by using the diagonalization of the complete energy matrix for 3d2 ions in trigonal symmetry. The crystalfield parameters are estimated for the superposition model related to the local geometry (or structure) of the impurity centers. From the calculations, the EPR parameters for both impurity centers are explained and the local structures (characterized by the impurity displacement Δz along the C3 axis and the displacement Δx of O2− ions in the oxygen triangle between the impurity and the vacant oxygen octahedron along the x-axis, resulting from the electrostatic repulsive force and the electronic cloud overlap) of these impurity centers are estimated. The results are discussed.

STUDIES OF THE SPIN-HAMILTONIAN PARAMETERS AND OPTICAL SPECTRUM BAND POSITIONS FOR THE Yb(3+) ION IN Tm(3)Al(5)O(12) CRYSTALS

The spin-Hamiltonian parameters (g factors g(i) and hyperfine structure constants A(i), where i = x, y, z) and optical spectrum band positions of the Yb(3+) ion in the rhombically-distorted Tm(3+) site of Tm(3)Al(5)O(12) garnet crystal are calculated by a complete diagonalization (of the energy matrix) method, in which the Zeeman and hyperfine interaction terms are also included in the conventional Hamiltonian. From the calculations, the observed spin-Hamiltonian parameters of Tm(3)Al(5)O(12):Yb(3+) are explained reasonably and the optical spectrum band positions are suggested. The rationality of these suggested optical spectrum band positions is discussed by comparing them with the observed values of Yb(3+) ions in similar aluminum garnet (Yb(3)Al(5)O(12), Y(3)Al(5)O(12) and Lu(3)Al(5)O(12)) crystal.