Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 226
Absorption bands due to OH in glasses, and the solubility of water in glasses has been
studied extensively in the literature [11-21]. Adams found that association of OH groups
through hydrogen-bonding in silicate glasses produces three effects on infrared OH
absorption bands [11]:
1. decrease of the frequency of asymmetric stretching bands;
2. enhancement of the integrated intensity and
3. broadening of the contour of absorption bands.
In general, multiple hydrogen-bonded OH absorption bands are found for silicate glasses
only when modifiers (Na + , K + ) and / or intermediates (Ca 2+ , Pb 2+ ) are present, as the
electronic structure of the oxygen atom changes, the field strength increases and the
greater negative charge on the oxygen atom results in greater affinity for hydrolysis to
occur [11]. Scholze [17] identified a number of vibrational absorption bands for silicate
glasses which will be discussed in more detail later in this section, in relation to tellurite
and fluorotellurite glasses. He found that vitreous silica possessed a single absorption
band around 3675 cm -1 attributed to ‘free-OH’, which exhibits no hydrogen-bonding.
Like Adams, Scholze found by adding alkali metal oxides such as Na2O that this band
gradually shifted to longer wavelengths eventually overlapping with a band around 3000
cm -1 not present in the spectrum of vitreous silica. This band, and another at around 2300
cm -1 , was attributed to OH in the glass, which participates in hydrogen bonding of
varying bond-strength and length [17]. Zarubin [19] has recently challenged this model
by suggesting the bands around 3000, 2300 and a further band at 1800 cm -1 are the result