Electron paramagnetic resonance and optical study of VO ~(2+)-doped zinc ammonium phosphate hexahydrate single crystals

摘要

Electron paramagnetic resonance(EPR) and optical studies of VO ~(2+) ions in zinc ammonium phosphate hexahydrate ZnNH _4PO _4·6H _2O(ZAPH) single crystals were carried out at room temperature. Analysis of EPR spectra indicates the presence of two distinct VO ~(2+) sites. The angular variations of EPR spectra in three mutually perpendicular planes ab, bc and ca are used to determine the principal axes and values of the tensors g and A. The spin Hamiltonian(SH) parameters are obtained using Schonland's method as: g _x=1.9967, g _y=1.9767, g _z=1.9668, A _x=62, A _y=70, A _z=172(×10 ~4)cm ~1 for site I, whereas g _x=1.9998, g _y=1.9820, g _z=1.9698, A _x=54, A _y=60, A _z=149(×10 ~4)cm 1 for site II. The optical absorption study at room temperature is also carried out and the absorption bands are assigned to various transitions. The theoretical band positions are calculated using approximate energy expressions. Good agreement is obtained between theoretical and experimental band positions. By correlating EPR and optical data, various molecular orbital coefficients of the vanadyl ion in the ZAPH lattice are evaluated and the nature of bonding in the crystal is discussed.