Effect of alkaline earths on spectroscopic and structural properties of Cu 2+ ions-doped lithium borate glasses Ashok Bhogi a , R. Vijaya Kumar b , P. Kistaiah c, ⁎ a VNR Vignana Jyothi Institute of Engineering and Technology, Hyderabad, Telangana, India b School of Physics, University of Hyderabad, Hyderabad, Telangana, India c Department of Physics, Osmania University, Hyderabad, Telangana, India abstract article info Article history: Received 18 April 2015 Received in revised form 31 May 2015 Accepted 10 June 2015 Available online xxxx Keywords: Lithium borate glass; X-ray diffraction; Electron paramagnetic resonance; Optical absorption; FTIR spectroscopy Alkaline earth lithium borate glasses with composition 15RO–25Li 2 O–(60-x)B 2 O 3 : xCuO (where R = Ca, Ba and x = 0, 0.4 and 0.8) were prepared by the conventional melt quenching technique. X-ray diffractograms confirm the amorphous nature of the glass samples. Spectroscopic studies such as optical absorption, EPR and FTIR were used to understand the effect of modifier oxide and CuO dopant in the glass matrix. From the optical absorption spectra the absorption band which is attributed to the 2B 1g → 2B 2g characteristic transition of Cu 2+ ions in the distorted octahedral sites. The cut-off wavelength (λ c ), optical band gap (E opt ), and Urbach energy (ΔE) were also determined. The average electronic polarizability of the oxide ion α o2- (E opt ), optical basicity Λ(E opt ) and Yamashita–Kurosawa's interaction parameter A(E opt ) were also examined. From the EPR spectra the spin- Hamiltonian parameters are evaluated. The values of spin-Hamiltonian parameters indicate that the site symme- try around Cu 2+ ions is tetragonally distorted octahedral. Using electron paramagnetic resonance (EPR) and op- tical absorption data, the molecular orbital coefficients α 2 and β 2 1 are calculated. The FTIR studies show that these glasses are made up of BO 3 and BO 4 units. The variation of optical and spectroscopic parameters was discussed in terms of the ionic radius of alkaline earth metal modifier. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Glass materials play an important role in various fields like Science, Medicine, Industry etc. and are transparent in the visible spectrum. Glasses are amorphous materials and exhibit the optical isotropy [1,2]. Because of greater refractive index, the borate glasses containing boron oxide have been used for optical lenses. The addi- tion of alkali oxides such as Li 2 O, K 2 O, and Na 2 O may improve their physical properties and preparation conditions [3,4]. Lithium borate glasses have attractive considerable scientific interest because they are used for detecting penetration of radiation in homeland security [5]. These glasses have been well studied over the past decade and there has been much interest in their structure and spectra. This in- terest is due to the anomalous behavior of the borate glass in that it forms super structural units such as BO 3 and BO 4 units. BO 3 has a pla- nar triangle where as BO 4 has a tetrahedral arrangement of oxygens around the boron atom [6–8]. These two super structural units can be combined to form either the so-called super cooled liquid or differ- ent structural groups like diborate, tetraborate, pentaborate, boroxol rings etc. [9–12]. Boric acid (B 2 O 3 ) is one of the best glass former, when it is incor- porated with glass modifiers such as Li 2 CO 3 ,K 2 CO 3 , and Na 2 CO 3 its internal structure is rearranged due to the formation of non- bridging oxygens [13]. The addition of alkali, alkaline earth oxides (Li 2 O, K 2 O, Na 2 O, CaO, SrO, BaO) to borate glasses improve their physical properties, glass forming capability, increase their resis- tance to moisture and modify the host structure through the conver- sion of the structural units of the borate system from triangular BO 3 units to tetrahedral BO 4 units [14]. Transition metal ions have strong bearing on the optical, magnetic, and electrical properties of glasses. A large number of interesting studies have been available on the environment of transition metal ions in var- ious inorganic glass systems. The transition metal oxide such as CuO is chosen in the present investigation because it exists in two different va- lence states i.e. monovalent Cu 1+ and divalent Cu 2+ and that it can also represent as CuO 4 and CuO 6 in the glass network [15,16]. Many re- searchers have reported that the addition of CuO in the glass structure makes the glass electrically semiconducting and super paramagnetic [17,18]. The main objective of this paper is to study the influence of different modifier oxides (CaO and BaO) and copper doping concentra- tion on the optical absorption, EPR and FTIR spectra of 15RO– 25Li 2 O–(60-x)B 2 O 3 –xCuO (R = Ca and Ba) glass system. It is also expected that this investigation helps to identify suitable glass composi- tion for optical applications. Journal of Non-Crystalline Solids 426 (2015) 47–54 ⁎ Corresponding author. E-mail address: pkistaiah@yahoo.com (P. Kistaiah). http://dx.doi.org/10.1016/j.jnoncrysol.2015.06.012 0022-3093/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol