EPR and Optical Absorption Study of VO 2+ Ions Doped Potassium Hexaaquazinc (II) Sulfate Single Crystals
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Applied Magnetic Resonance
EPR and Optical Absorption Study of VO2+ Ions Doped Potassium Hexaaquazinc (II) Sulfate Single Crystals Ram Kripal • Madan Gopal Misra
Received: 20 June 2012 / Published online: 23 April 2013 Ó Springer-Verlag Wien 2013
Abstract X-band single-crystal electron paramagnetic resonance (EPR) studies are done on VO2? ions doped in potassium hexaaquazinc (II) sulfate, K2[Zn (H2O)6] (SO4)2 (PHZS) at room temperature. The spin Hamiltonian parameters, i.e., g and A tensors and their direction cosines, are evaluated by the standard diagonalization procedure using angular variation of the EPR spectra in three planes (ab, bc* and c*a), with the help of a computer program. The EPR spectrum is simulated using the EasySpin program to verify the calculations. The detailed EPR analysis indicates the presence of two magnetically inequivalent VO2? sites. Both the vanadyl complexes are found to take up the substitutional position in the host lattice. The optical absorption spectrum of VO2? ions doped in PHZS single crystal at room temperature is also recorded and four main d–d transfer bands in the visible region are assigned. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. With the help of assigned bands the crystal-field parameters (Dq, Ds and Dt) are evaluated. Finally, with the optical and EPR data, the nature of bonding in the complex is discussed. 1 Introduction Electron paramagnetic resonance (EPR) technique is widely used to determine the symmetry of the crystal field produced by the ligands around the magnetic ions used as a probe in the host lattices. This method is used as a tool for understanding R. Kripal (&) M. G. Misra E. P. R. Lab., Department of Physics, University of Allahabad, Allahabad, U.P., India e-mail: [email protected] M. G. Misra e-mail: [email protected] M. G. Misra Department of Physics, C. A. V. Inter College, Allahabad, U.P., India
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physical properties of radicals, reactive radical intermediates or metal centers in organic and inorganic molecules [1–3]. The optical absorption study provides the structure of energy levels of the metal ion and the crystal field parameters. Thus EPR and optical absorption are two powerful complementary tools for investigating the dynamic behavior of metal ions in crystals. The vanadyl ion, the most stable molecular metal ion with d1 configuration, allows paramagnetic resonance to be observed at ambient temperatures [4, 5]. The interesting behavior of the VO2? ion in different host lattices is due to the different orientations of the strong V = O bond. Due to the short V = O bond, the unpaired electron is always in a non-degenerate state leading to wellresolved EPR spectra. The VO2? ion is the simplest paramagnetic probe that can easily be incorporated into a number of host lattices to get information about the type of distortion, delocalization of electrons, and also structural phase transitions. It can exi
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