Journal of the Korean Physical Society, Vol. 68, No. 8, April 2016, pp. 998∼1007 Spectroscopic and Optical Properties of the VO 2+ ion doped TeO 2 -TiO 2 -ZnO-Nb 2 O 5 glass system Swapna, G. Upender, V. Sreenivasulu and M. Prasad ∗ Glassy Materials Research Laboratory, Department of Physics, Osmania University, Hyderabad, India (Received 12 October 2015, in final form 10 March 2016) Studies such as optical absorption, Fourier transform infrared spectroscopy (FTIR), Raman spec- troscopy, Electron paramagnetic resonance (EPR) spectroscopy and Differential scanning calorime- try (DSC) were carried out on VO 2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system. Raman and FTIR spectra of the glasses revealed the presence of [TeO3], [TeO4] and [NbO6] structural units in the glass network. The Urbach energy (ΔE), cut-off wavelength (λc), optical band gap (Eopt ), optical basicity (Λ) and electron polarizability (α) of the glasses were determined from optical ab- sorption studies. The density (ρ), molar volume (Vm), oxygen molar volume (Vo) and refractive index (n) were also measured. Spin-Hamiltonian parameters were calculated from the EPR studies. When Nb2O5 was increased at the expense of ZnO, the density, optical band gap and Urbach en- ergy of the glasses increased, and the electronic polarizability and optical basicity decreased. The EPR spectra clearly showed that vanadium was in the glass as VO 2+ and occupied octahedral sites with tetrahedral compression. Spin-Hamiltonian parameters g ‖ and g ⊥ decreased as Nb2O5 content increased in the glass. The glass transition temperature (Tg ) also increased with increasing Nb2O5 content in the glass. PACS numbers: 78.30.Am, 33.35.+r, 61.43.Dq, 81.05.Kf Keywords: Raman spectra, FTIR spectra, Optical absorption, EPR, VO +2 spin probe DOI: 10.3938/jkps.68.998 I. INTRODUCTION In recent years there has been considerable interest in preparation of heavy metal oxide glasses due to the fact that they possess some interesting nonlinear prop- erties like high third-order susceptibilities and high re- fractive indices [1]. TeO 2 is a conditional glass former and in combination with other heavy metal oxides like Bi 2 O 3 , Sb 2 O 3 , WO 3 , Nb 2 O 5 and As 2 O 3 produces glasses with some enhanced properties [2]. Tellurite glasses are widely used in optical switching, wavelength conversion and optical amplifiers. TeO 2 -Nb 2 O 5 glasses exhibit a wide transition range, high linear and non linear refrac- tive index, high density, good chemical durability, low glass transition temperature and good glass stability [3– 7]. These properties are due to high polarizability of Te 4+ ions. These properties can be enhanced even more by the incorporation of other heavy metal oxides. The addition of Ti 4+ and Nb 5+ ions has been reported to lead to significant changes in the physical properties, espe- cially, the optical properties of TeO 2 glasses. The struc- ture of pure Tellurite glass is unstable because of its lack of linkage between Te-O chains; some modifier ions such as zinc, titanium and niobium have to be introduced to ∗ E-mail: prasad5336@yahoo.co.in improve the linkages in TeO 2 glasses [8]. This process not only improves the linkages but also helps strengthen the glass by improving the stability of the glass. The ad- dition of these network modifiers also affects the optical properties, glass transition temperature and performance of the glass. In TeO 2 -Nb 2 O 5 glasses, Te-O-Nb bonds are present, and these bonds increase with increasing in Nb 2 O 5 content. In TeO 2 -Nb 2 O 5 glasses, the NbO 6 oc- tahedral plays a significant role in the glass network [9]. Studies have been carried on TeO 2 -Nb 2 O 5 -TiO 2 glasses and TeO 2 -Nb 2 O 5 -ZnO glasses and their properties [10]. When niobium ions are introduced in the glass network, they connect Te-O chains, stabilize the glass network, and provide some oxygen ions for changing the tellurium oxide coordination polyhedra [11]. The structure of the tellurite glass consists of a three-dimensional network of TeO 4 units linked by Te-O-Te linkages. The addi- tion of Nb 2 O 5 glass modifier changes the coordination of TeO 4 trigonal bipyramids (tbp) to TeO 3 trigonal pyra- mids (tp) through an intermediate polyhedral TeO 3+1 unit [12]. Addition of Nb 2 O 5 to tellurium glass improves the third-order non-linear optical property of the tellu- rite glass. The relatively large refractive indices of the tellurium niobate glasses are attributed to the hyper po- larizability of Nb-O bonds [13]. EPR studies on alkali oxide based TeO 2 glasses with -998-