Theoretical studies of the optical and EPR spectra for VO2+ in MgKPO4·6H2O single crystal

•The tetragonal field parameters are associated with the local structures of the impurity V4+ center.•Ligand contributions are taken into account from the cluster approach.•EPR and optical spectra are analyzed for the impurity V4+ center in the MPPH crystal.

The optical absorption and electron paramagnetic resonance (EPR) parameters (g factors g||, g⊥ and hyperfine structure constants A||, A⊥) of a tetragonal V4+ center in MgKPO4·6H2O (MPPH) crystal are theoretically investigated using the perturbation formulas for a 3d1 ion in tetragonally compressed octahedra. In these formulas, the contributions from the s- and p-orbitals as well as the spin–orbit coupling coefficient of the O2− ligand are taken into account based on the cluster approach. The calculated results are in good agreement with the observed values. The local structure parameters of the [VO6]8− cluster are obtained from the calculation. The magnitudes of the metal–ligand distances parallel and perpendicular to the C4-axis are, respectively, R||≈1.846 Å and R⊥≈2.032 Å. The validity of the calculated results has also been discussed.