EPR and optical absorption of VO2+ impurity in lithium potassium sulphate single crystal

Electron paramagnetic resonance (EPR) and optical absorption studies of VO2+ doped lithium potassium sulphate single crystals are carried out at room temperature. The angular variation of the spectra is studied in the crystallographic a*b, bc and ca* plane. Vanadyl is found to have fixed orientations in the lattice and there are two magnetically inequivalent complexes in the lattice. The spin Hamiltonian parameters obtained from single crystal data for the two sites are, Site I: gxx=2.0015±0.0002, gyy=1.9835±0.0002, gzz=1.9211±0.0002, Axx=(48±2)×10−4 cm−1, Ayy=(64±2)×10−4 cm−1, Azz=(169±2)×10−4 cm−1, Site II: gxx=2.0019±0.0002, gyy=1.9796±0.0002, gzz =1.9225±0.0002, Axx=(48±2)×10−4 cm−1, Ayy=(83±2)×10−4 cm−1, Azz=(178±2)×10−4 cm−1. The first three bands observed in optical absorption spectrum are attributed to d-d transitions and the last band is probably charge transfer band. The band positions are calculated using energy expressions and compared with the observed values to confirm the transitions. Crystal field parameter (Dq) and tetragonal parameters (Ds and Dt) are also evaluated. Using EPR and optical results, the molecular orbital parameters of VO2+ ions in the lattice are evaluated with a tetragonal symmetry approximation (because the rhombic part is small) and the nature of bonding in the complex is discussed.