Glass, hydroxyl bonds containing

PERSISTENT SPECTRAL HOLE-BURNING FOR THE SOL-GEL GLASSES CONTAINING HYDROXYL BONDS... 

Virtually all oxide glasses contain chemically bonded water in the form of various types of hydroxyl (Si-OH, Ge-OH, etc.), while other protonic species, including silanes (Si-H, Ge-H, etc.), or molecular hydrogen, may or may not be present. Since the effect of water on the optical and physical behavior of glasses is so important, discussion of these species merits a separate chapter. A detailed discussion of the formation of bound hydrogen species, their effect on the optical spectra and physical properties of glasses, and the diffusion and solubility of water in glasses and melts is found in Chapter 11. 

Virtually all oxide glasses contain hydroxyl in various forms, while other molecular species may or may not be present. The primary absorption band due to Si-OH bonds occurs at 3673 cm" for vitreous silica (Figure 11.1). Since this is a vibrational absorption, overtones occur at V2, 7J3, etc. Other bands due to hydroxyl arise from the combination of the Si-OH frequencies with fundamental Si-O vibrations. These overtone and combination bands are relatively weak and are not of much importance for thin samples. However, when one forms an extremely long (km) optical fiber from vitreous silica, these bands, which occur within the optical windows used for telecommunication systems, become significant and must be eliminated to reduce optical losses to acceptable levels for these systems. Many millions of dollars have been invested in the research leading to the effective elimination of these very weak infrared absorption bands. 

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