Electronic Structure of Ni2+ in MgF2 and ZnF2

Abstract

The absorption spectra of nickel (II) in MgF₂ and ZnF₂ are reported. The important feature of the spectra is that the first spin‐allowed absorption band shows strongly polarized line structure. From its polarization, the mechanism of the absorption for this line structure has been determined to be magnetic dipole. Furthermore, together with its temperature dependence, symmetry assignments have been made for the fine structure of ³T₂ and the ground state. The energy separations and assignments of the ground state thus determined are compatible with the results of electron spin resonance. Choosing two parameters of the orthorhombic field so as to fit the energy separations of the ground state, each energy level of ³T₂ under the combined action of the spin orbit force and orthorhombic fields has been calculated as a function of two remaining parameters and compared with experiment. The values of the four parameters and the discrepancy with experiment are discussed. It is shown that the effective Hamiltonian approach for ³T₂ is as good as the configuration interaction approach including all the states of d⁸ electron configuration, provided the second‐order effect of the spin—orbit interaction is included. As one of possible mechanisms to remove the discrepancy with experiment within the framework of the crystal field theory, Jahn—Teller distortions of the ³T₂ state are considered.