Synthesis, characterization and optical properties of non-traditional tellurite–selenite glasses A. Bachvarova-Nedelcheva a,⇑ , R. Iordanova a , K.L. Kostov a , V. Ganev b , St. Yordanov c a Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria b Institute of Mineralogy and Crystallography ‘‘Acad. I. Kostov’’, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria c Central Laboratory of Solar Energy and New Energy Source, 72, Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria article info Article history: Received 23 July 2013 Received in revised form 22 January 2014 Accepted 17 March 2014 Available online 6 April 2014 Keywords: Tellurite–selenite glasses Network formers Structure Charge transfer Red colored glasses abstract This study continues our investigations on non-traditional tellurite–selenite amorphous materials. Two glasses containing TeO 2 , SeO 2 , MoO 3 and V 2 O 5 were obtained at high oxygen pressure (P = 36 MPa) using pure oxides as precursors. The real bulk chemical composition of both glasses was verified by LA-ICP-MS method. The glasses were characterized by X-ray diffraction, Scanning Electron Microscopy (SEM), Differential Thermal Analysis (DTA), UV–Vis, XPS, IR and EPR spectroscopy. According to DTA the glass transition temperature (T g ) is below 300 °C. Both glasses were subjected to heat treatment (300 °C– 12 h) and as a result no crystallization was observed. The main building units (TeO 3 , TeO 4 , Mo 2 O 8 , and SeO 3 ) were determined by IR and X-ray photoelectron spectroscopy and the existence of mixed bridging bonds only, which build up the amorphous network. It was established by UV–Vis that the obtained glasses are transparent above 550 nm and they were red colored. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction The synthesis and characterization of tellurite glasses was widely studied in the Department of Silicate technology in UCTM – Sofia and in the 1980–1990s years of the XX century this topic was a traditional subject for the Department [1–3]. A lot of data for tellurite glasses was collected in the Mallawany’s monography [4]. Although TeO 2 cannot be vitrified alone by traditional meth- ods, high transparent tellurite glasses could be obtained simply by introducing other metal oxides (e.g. transition metal oxides, alkaline oxides and alkaline-earth oxides) without the addition of any conventional glass former, which was first reported by Rawson and Stanworth [5,6]. The tellurite glasses continue to pro- voke interest due to their high refractive indices, low melting tem- peratures and high dielectric constants as well as their good infrared transmissions. It is well known that they are considered as promising materials for non-linear optical devices [4,7–11], optical fiber amplifiers [12], electronic switching effects [13], etc. Quite recently, metal oxides such as Bi 2 O 3 , Sb 2 O 3 , MoO 3 and Nb 2 O 5 have been added to the tellurite glass system in order to enhance their optical behavior [14–16]. Obviously, the investigations on the structure and properties of different multi- component tellurite glasses are still not exhausted. On the other hand, selenite glasses are a new exotic class of non-traditional glasses that have not been enough studied up to now. As it is well known the main difficulty in the synthesis of this type of glasses is the rapid volatilization of selenite melts and the sublimation of SeO 2 at atmospheric pressure and temperatures above 315 °C. It was already established that in different two-, three and multi- component selenite systems it is possible to obtain a selenite glass even at a low cooling rate, particularly if the second components are also glass-forming oxides [17,18]. In our previous investiga- tions different colored selenite glasses with specific optical prop- erties were obtained [19]. Some complicated compositions should be potential candidates for technological applications as amorphous semiconductors and superionic materials, infrared transmission components, in non-linear optical devices, sensors, reflecting windows, soluble microfertilizers, etc. [20–27]. The main advantage of the introduction of SeO 2 is its ability to decrease the melting temperature of glass compositions and to modify their optical properties [28–31]. Recently, our team obtained an orange colored glass containing TeO 2 , SeO 2 , MoO 3 and La 2 O 3 and its thermal stability, local order as well as optical properties were investigated [33]. Moreover, the ac- tual chemical composition of the glass was determined by different analytical methods in order to verify the content of SeO 2 and TeO 2 . http://dx.doi.org/10.1016/j.optmat.2014.03.022 0925-3467/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +359 (2) 979 63 17; fax: +359 (2) 870 50 24. E-mail address: albenadb@svr.igic.bas.bg (A. Bachvarova-Nedelcheva). Optical Materials 36 (2014) 1319–1328 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat