Investigations of the spin Hamiltonian parameters and defect structure for the rhombic Gd3+ center in calcium oxide

Abstract

The spin Hamiltonian (SH) parameters (zero-field splittings , and ) and the defect structure for the rhombic Gd3+ center in CaO are theoretically investigated by the superposition model. Meanwhile, the g-factor is also quantitatively studied from the approximation formula on the basis of an admixture of the ground 8S7/2 and the excited 6L7/2 (L = P, D, F, G) states via the spin–orbit coupling interactions. The defect structure of this center can be described by the impurity Gd3+ occupying the host octahedral Ca2+ site, associated with one nearest neighbouring cation vacancy V Ca in the [1 1 0] direction. On the basis of these studies, the impurity Gd3+ is found to shift towards the V Ca along the [1 1 0] axis by about 0.582 Å, whereas the oxygen ligands closest to the V Ca suffer a displacement towards the latter by about 0.211 Å. The calculated SH parameters based on the earlier analyses show reasonable agreement with the observed values.