Crystal-field hamiltonian and spin-orbit interaction for d2 and d8 ions at low C3 symmetry sites: V3+:Al2O3 and Ni2+:LiNbO3

The experimental studies have provided evidence of the occurrence of transitions from the 3T1g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3P) and 3A2g(3F) for the V3+ centres in Al2O3 crystal; and from the 3A2g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3F) and 3T1g(3P) for the Ni2+ centres in LiNbO3 crystal (levels are assigned to irreps of the Oh point symmetry group). Using the experimental spectroscopic data, theoretical calculations of the crystal-field levels of V3+:Al2O3 and Ni2+:LiNbO3 are carried out based on the Racah theory. The observed crystalline-field splittings of the V3+ and Ni2+ terms were accounted for using a C3 symmetry Hamiltonian. The spin-orbit interaction was taken into account in this work. The Racah, crystal-field and spin-orbit parameters, which fit experimental and theoretical energy levels, have been reliably obtained. A good agreement between the theoretical and experimental results for the energy levels of V3+:Al2O3 and Ni2+:LiNbO3 has been obtained.