Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 227
of an ABC triplet due to a single type of hydrogen-bonded-OH, and not variation of OH
bond distances / strength in the network.
The glasses shown in fig. (6.6), of the series (80-x)TeO2-10Na2O-10ZnO-xMO, where
MO is PbO or GeO2, for MOD006 (x = 3 mol. % PbO), MOD010 (x = 5 mol. % PbO)
and MOD012 (x = 5 mol. % GeO2), exhibited two bands in the mid-infrared attributed to
OH species. The presence of OH in the glass indicated the batch materials may have been
contaminated with hydroxide (see chapter 5), and entrapped water, and / or water entered
the glass via the furnace atmosphere and hydrolysed the glass melt producing hydroxide.
The lower frequency band at around 2300 cm -1 (4.5 µm) has previously in the literature
been attributed to H-bonded OH [8]. The more intense band around 3000 cm -1 (3.5 µm)
has previously been attributed to free-OH [8] and appears here to incorporate a higher
wavenumber shoulder at around 3300 cm -1 (3.0 µm). It has been shown in alkali and
alkaline earth silicates that the analogous band can be deconvoluted into several Gaussian
spectral components [20], and similar behaviour has been observed here as shown by fig.
(6.8) to (6.10). For the tellurite glasses in this study, the lower frequency band (strongly
H-bonded OH) at ≈ 2300 cm -1 was found to be lower in intensity, and sharper than the
higher frequency band (free OH) at ≈ 3000 cm -1 ; these intensities are the converse of the
effects observed by Adams [11]. One possibility is that the tellurite glasses are relatively
dry, therefore the OH in the bulk of the glass has fewer OH groups nearby for hydrogen-
bonding to occur [5], although H-bonding will still occur with other oxygens in the glass
network. This disparate trend in OH band intensities compared to silicates could be due
to the equilisation of charge distributions in bridging, and non-bridging oxygens in