Synthesis, structural, thermal and optical properties of TeO 2 eBi 2 O 3 eGeO 2 eLi 2 O glasses Louiza Dimowa a , Iskra Piroeva b , S. Atanasova-Vladimirova b , Nadia Petrova a , Valentin Ganev a , Rositsa Titorenkova a , Georgi Yankov c , Todor Petrov c , Boris L. Shivachev a, * a Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Building 107,1113 Sofia, Bulgaria b Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. Georgi Bonchev str., Building 11, Sofia 1113, Bulgaria c Institute of Solid State Physics, Acad. G. Nadjakov, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria article info Article history: Received 22 April 2016 Received in revised form 1 August 2016 Accepted 6 September 2016 Keywords: Tellurite glasses XRD Raman SHG abstract In this study, synthesis and characterization of novel quaternary tellurite glass system TeO 2 eBi 2 O 3 eGeO 2 eLi 2 O is presented. The compositions include TeO 2 and GeO 2 as glass formers while different proportion of Bi 2 O 3 and Li 2 O act as network modifiers. Differential thermal analysis, X-ray diffraction, scanning electron microscopy energy dispersive X-ray spectroscopy, laser ablation inductively coupled plasma mass spectrometry, UVeVis and Raman spectroscopy are applied to study the structural, thermal and optical properties of the studied glasses. Obtained glasses possess a relatively low glass transition temperature (around 300  C) if compared to other tellurite glasses, show good thermal transparency in the visible and near infra-red (from 2.4 to 0.4 mm) and can double the frequency of laser light from its original wavelength of 1064 nm to its second-harmonic at 532 nm (i.e. second harmonic generation). © 2016 Elsevier B.V. All rights reserved. 1. Introduction Nowadays, there is an increasing fundamental and technological interest in studying materials which possess non-linear optical properties, ranging from frequency doubling or tripling (second harmonic generation (SHG) and third harmonic generation), self- focusing or defocusing, phase matching, etc. [1e13]. The great in- terest in studying tellurite glasses is related with their electrical and nonlinear optical properties [14e16]. Though the focus of the preparation of TeO 2 based glasses, ceramics etc. materials rely on their optical properties and applications they are also studied for alternative preparation methods (e.g. sol-gel) and uses [17e20]. Tellurite glasses exhibit high nonlinear refractive index (usually around and above 2), low phonon maximum, wide infrared trans- mittance (from 0.3 up to 3 mm), high dielectric constant and lower melting point than SiO 2 [21e24]. It is known that GeO 2 glass has good optical, transparency in the mid infrared region and nonlinear properties [25,26]. However, the TeO 2 e GeO 2 system is not attractive because resultant glassy matrices are taught to be unstable and nonhomogeneous [27e30]. Interestingly, we found that the TeO 2 eBi 2 O 3 eGeO 2 , TeO 2 eGeO 2 eLi 2 O glasses and similar TeO 2 -based glass systems exhibit second-harmonic generation with and without the use of electro-thermal poling [31e36]. As a continuation of our studies we report herein the synthesis, struc- tural and optical properties for ternary glass compositions (100-4x) TeO 2 e2xBi 2 O 3 exGeO 2 exLi 2 O, where x is in the range 2.5e10 mol%. 2. Experimental details 2.1. Glass preparation Three powder batches of TeO 2 eBi 2 O 3 eGeO 2 eLi 2 O with pro- portions of 90:5:2.5:2.5, 80:10:5:5 and 60:20:10:10 mol% were prepared (each batch weighted around 8 g). The powders were carefully mixed, were placed in platinum crucibles and were mel- ted in a furnace at 920  C for 50e60 min. After reaching 920  C the crucible was shaken every 15 min in order to achieve material homogeneity. The glasses were obtained by conventional melt- quenching method. The high-temperature melt was poured onto a stainless steel plate preheated at 160e170  C and allowed to relax at this temperature for 12 h in a separate furnace. The furnace was then switched off and the samples were allowed to cool down to * Corresponding author. E-mail addresses: blshivachev@gmail.com, bls@clcmc.bas.bg (B.L. Shivachev). Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat http://dx.doi.org/10.1016/j.optmat.2016.09.008 0925-3467/© 2016 Elsevier B.V. All rights reserved. Optical Materials 60 (2016) 577e583