Studies of the spin-Hamiltonian parameters, d-d transitions and defect structures for two tetragonal Cu2+ centers in Ba2ZnF6:Cu2+ crystal

Two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), are applied to calculate the spin-Hamiltonian parameters (g-factors g∥, g⊥ and hyperfine structure constants A∥, A⊥, obtained from electron paramagnetic resonance (EPR) spectra) and d-d transitions (obtained from optical spectra) for two tetragonal Cu2+ centers in Ba2ZnF6:Cu2+ crystals. The Cu2+(I) ion replaces the Zn2+ ion at tetragonally compressed octahedral coordination and has the ground state 2A1(|dz2〉), whereas the Cu2+(II) ion is at an interstitial site with a square-planar F−coordination and has the ground state 2B2(|dx2-y2〉). The calculated spin-Hamiltonian parameters and d-d transitions from the PTM and CDM coincide and are in reasonable agreement with the experimental values. This suggests that both methods are effective for the theoretical studies of EPR and optical spectral data for 3d9 ions in tetragonal symmetry with different ground states. The defect structures of the two Cu2+ centers in Ba2ZnF6:Cu2+ are also estimated.