Abstract
Mixed alkali and alkaline earth oxide glasses of RO-Li2O-Na2O-K2O-B2O3(R = Zn, Mg, Sr and Ba) system were studied by electron paramagnetic resonance (EPR) and optical absorption spectroscopy. Cu2+ and VO2+ ions were used as the spin probes. The glasses containing 1 mole% of Cu2+ and 2mole% of VO2+ were prepared by the melt quenching method. X-ray diffraction studies of the samples did not reveal crystalline phases. EPR measurements were made at X-band frequencies with 100 kHz field modulation, at 310 K. Optical spectra were recorded in the wavelength range 300 nm - 800 nm. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values in the case of Cu2+ indicated that the ground state of Cu2+ was orbital (2B1g) and the site symmetry around Cu2+ is tetragonally distorted octahedral. The variation of gll and All with the alkaline earth oxide (RO) composition was found to be non-linear which may be due to the change in the ligand field strength at the site of Cu2+ ions. From the spin-Hamiltonian parameters of VO2+, it was observed that the vanadyl ions exist as VO2+ ions in octahedral coordination with tetragonal compression and have C4V symmetry with ground state dxy. Tetragonality (△gll/△g) of V4+ ion sites exhibited non-linear variation with RO content, which indicated change in the ligand field at the site of V4+. A broad optical absorption band was observed in the glass containing Cu2+ ions corresponding to the 2B1g → 2B2g transition. From the EPR and optical data the bond parameters were evaluated. In the case of VO2+ ions, the covalency rates were estimated.
Highlights
Electron Paramagnetic Resonance (EPR) spectroscopy is an experimental technique to obtain information on some of the structural and dynamic phenomenon of a material and to identify the site symmetry around the transition metal (TM) ions in glasses
The starting materials used in the present study were analytical grade lithium carbonate (Li2CO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), zinc oxide (ZnO), magnesium oxide (MgO), strontium oxide (SrO), barium oxide (BaO) and boric acid (H3BO3)
The optical absorption spectra of the glasses containing copper were recorded at room temperature (310 K) using UV-VIS spectrophotometer (Shimadzu) in the wavelength region 300 nm to 1100 nm
Summary
Electron Paramagnetic Resonance (EPR) spectroscopy is an experimental technique to obtain information on some of the structural and dynamic phenomenon of a material and to identify the site symmetry around the transition metal (TM) ions in glasses. Glasses doped with TM ions have attracted a great deal of attention because of their potential applications in the development of new tunable solid-state lasers, solar energy converters. It has been well established [1,2,3,4,5] that alkali borate glasses can be used as solid electrolytes, in solid state batteries. Electrical conductivity, EPR and optical studies were carried on double alkali (mixed alkali) borate glasses by several wsorkers [6,7,8]. It is interesting to study the effect of the two paramagnetic probes (Cu2+ and VO2+) on the structural aspects of the glasses
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