Electron paramagnetic resonance and optical study of VO2+-doped zinc ammonium phosphate hexahydrate single crystals

• Published in: Physica scripta Vol. 86; no. 4
• Main Authors: Kripal, Ram, Misra, Madan Gopal, Lipinski, I E, Rudowicz, C
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01-10-2012
• ISSN: 0031-8949; 1402-4896
• DOI: 10.1088/0031-8949/86/04/045602

Electron paramagnetic resonance (EPR) and optical studies of VO2+ ions in zinc ammonium phosphate hexahydrate ZnNH4PO4·6H2O (ZAPH) single crystals were carried out at room temperature. Analysis of EPR spectra indicates the presence of two distinct VO2+ 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: gx = 1.9967, gy = 1.9767, gz = 1.9668, Ax = 62, Ay = 70, Az = 172(×10−4) cm−1 for site I, whereas gx = 1.9998, gy = 1.9820, gz = 1.9698, Ax = 54, Ay = 60, Az = 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.