Modeling the zero-field splitting parameters and local structure of Co2+ ions doped into PbMoO4 crystal based on crystal field approach and superposition model analysis

Abstract

Superposition model (SPM) analysis is employed for determination of the crystal field parameters (CFPs) for Co2+ ions doped into PbMoO4 crystal. SPM calculations utilize structural data to model parameters spectroscopically measured for the dopant ions. The CFPs predicted by SPM assuming axial site symmetry serve as input for the CFA/MSH package, which incorporates the CF analysis (CFA) and the microscopic spin Hamiltonian (MSH) modules. This approach enables modeling of the optical energy levels as well as the axial SH parameters: zero-field splitting parameter (ZFSP) D and gi factors: g|| and g⊥. The theoretical SH parameters are matched with the ones deduced from experimental electron magnetic resonance (EMR; EPR) data for Co2+(3 d7) ion using projection of gi for the effective spin S˜=32 onto gi' for the fictitious spin S'=12. Various structural models are considered to predict the CFPs and thus ZFSPs. The local distortion polar angles Δθ in the vicinity Co2+ ions in PbMoO4 are obtained for tetrahedral (Mo6+) and dodecahedral (Pb2+) sites for two possible structural configurations, thus confirming the structural distortions induced by Co2+ doping. This enables discerning between Co2+ ions located at the Pb2+ sites and those at the Mo6+ sites. The experimental data available for one type of the two observed Co2+ complexes in PbMoO4 are reanalyzed.