Influence of SiO 2 on the structure and optical properties of lithium bismuth silicate glasses Neetu Ahlawat, Sujata Sanghi * , Ashish Agarwal, Rajni Bala Department of Applied Physics, Guru Jambheshwar University of Science & Technology, Hisar, Haryana 125001, India article info Article history: Received 30 January 2009 Received in revised form 9 October 2009 Accepted 9 October 2009 Available online 20 November 2009 Keywords: Heavy-metal oxide glasses FTIR Optical material Glass network abstract Bismuth silicate glasses containing lithium oxide with composition 20Li 2 O(80  x)Bi 2 O 3 xSiO 2 (5 6 x 6 70 mol%) have been prepared by melt-quench technique. Density (D), molar volume (V M ) and glass transition temperature (T g ) for all the glass samples have been measured. FTIR spectroscopy has been employed to investigate the structure of these glasses in order to obtain information about the com- petitive role of Bi 2 O 3 and SiO 2 in the formation of glass network. The increase of SiO 2 content in the glass matrix results in increasing the Si–O–Si bond angle and hence the ionicity of Si–O bond increases with decrease in Bi 2 O 3 /SiO 2 ratio. The optical transmittance spectra of all the glasses have been recorded in the wavelength range 200–3300 nm. The values of optical band gap (E g ) have been determined from the cutoff wavelength of these glasses. The average electronic polarizability of oxide ion (a 2 o ) and the optical basicity (K th ) have been estimated from the calculated values of the E g and were found to be dependent directly on Bi 2 O 3 /SiO 2 ratio. The variation in different physical parameters such as D, V M and T g and optical parameters; viz., E g , a 2 o , K th with Bi 2 O 3 /SiO 2 ratio have been analyzed and discussed in terms of change in the glass structure. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Heavy-metal oxide glasses with unconventional network for- mer Bi 2 O 3 have received a remarkable attention due to their wide applications in the field of glass ceramics, layers for optical and opto-electronic devices, thermal and mechanical sensors, reflecting windows, etc. [1–6]. With their excellent optical properties, these glasses are promising candidates for ultra fast optical switches, infrared transmission components and other photonic devices. Bis- muth oxide cannot form glass by itself like other traditional glass formers; however, it can form glass in the presence of conventional glass formers. In such binary glasses, high polarizing cations, Bi(III) ions can reduce its co-ordination number from six to three and the glass network may consist of both [BiO 6 ] highly distorted octahe- dral and [BiO 3 ] pyramidal units [7,8]. Bismuth silicate glasses are of great importance for their industrial and special applications as low-loss fiber optics, infrared transmitting materials or as active medium of Raman fiber optical amplifiers and oscillators [9–12]. The large polarizability and small field strength of Bi 3+ in oxide glasses make them suitable for optical devices such as ultra fast all optical switches, optical isolators, optical Kerr shutters (OKR) and environmental guidelines [13]. Also bismuthate glasses con- taining alkali oxide act as ionic conductors and possess high con- ductivity compared to other heavy metal glasses [14,15]. Wide transmitting window in the optical region having sharp cutoff in both ultraviolet–visible and infrared region may make these glasses useful in spectral devices [7]. Hazra et al. [7] used the Ra- man and IR spectra to investigate the structure of unconventional lithium bismuthate glasses over the wide range of alkali oxide and found that the structure of this unconventional binary glass system changes systematically with the increase of Li 2 O content. In Raman spectra, they observed a broad but strong band at 380 cm 1 as- signed to the Bi–O–Bi vibration of [BiO 6 ] octahedral units, and a weak band at 628 cm 1 assigned to the Bi–O– stretching vibra- tion (i.e., vibration of non-bridging oxygen) of the [BiO 6 ] octahedral units modified in presence of Li 2 O. Further, Tenny et al. [16] stud- ied the infrared spectra of some alkali silicate glasses and observed a main band at about 1000 cm 1 due to formation of SiO 4 tetrahe- dra with NBOs [17]. This band shifts to higher frequencies and its intensity increases, with increase in alkali oxide content. Pan et al. [12] had studied the Raman and IR spectra of bismuth silicate glasses to investigate their structure and found that these glasses are formed by bismuth–oxygen polyhedra with isolated SiO 2 tetra- hedra. Recently, ElBatal [18] studied the IR spectra of the bismuth silicate glasses over a wide range of composition. They observed two very prominent and sharp bands at 471–456 cm 1 and at 879–865 cm 1 in the mid-infrared region (2000–400 cm 1 ). The band at about 457 cm 1 is attributed to Bi–O bonds in [BiO 6 ] octa- hedral and shifting to higher wave number (471 cm 1 ) is due to the 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.10.018 * Corresponding author. Tel.: +91 1662 263384; fax: +91 1662 276240. E-mail address: sutkash@yahoo.com (S. Sanghi). Journal of Molecular Structure 963 (2010) 82–86 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc