Studies on the local angular distortions around the impurity Co2+ in CdCl2, CdBr2 and PbI2

Abstract

The local angular distortions around the impurity Co2+ in CdCl2, CdBr2 and PbI2 are theoretically studied from the perturbation formulas of the electron paramagnetic resonance (EPR) parameters, the g factors g // and g ⊥ and the hyperfine structure constants A // and A ⊥ for a 3d7 ion in trigonal symmetry. In these formulas, the contributions from the s-orbitals of the ligands, which were often ignored, are taken into account based on the cluster approach. By analyzing the EPR spectra, we find that the impurity-ligand bonding angles β related to the C 3 axis in the Co2+ impurity centers are different from the corresponding metal-ligand bonding angles βH in the hosts, characterized by the local angular distortions Δβ (=β−βH). The calculated EPR parameters, especially the anisotropies of the g and A factors for the studied systems based on the local angular distortions Δ β, show reasonable agreement with the observed values.