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Michael A. Piliavin
Germanate Glasses: Structure, Spectroscopy, and Properties
Publisher Artech House Boston, London 1993
Germanium Dioxide (GeO2) containing glasses have become important materials in the telecommunications and optics industries. Attempts to improve the transmission loss in optical fibers brought about the use of Germanium Dioxide to make better optical fibers. Germanate Oxyfluoride Systems were first considered because they show less light scattering than pure GeO2 glass. Glass forming GeO2 has a higher linear coefficient of thermal expansion (75x10-7/oC) than either glass forming silica or boron anhydride. High coefficient of thermal expansion has a great importance in industrial application where high vacuum seals with brass or copper are required.
Glasses in the ternary system possess a high linear coefficient of thermal expansion: (118- 160) x10-7/oC. This glasses weld to metal (copper or brass) at relatively low temperatures, 530- 640Oc. Multi-component Germanate compositions can produce glasses that possess a high refractive index gradient, making possible the creation of elements that are able to focus optical beams. Compared to Silicate and Borate systems, in Germanate systems, higher refractive indices (1.80 or more) can be obtained for considerably smaller concentrations of the heavy elements oxides (PbO, Bi2O3, Nb2O5, Ta2O5, TiO2). For refractive indices in the range of nD= 1.60- 1.65, these oxides are not even required. Glass forming GeO2 has unusually high Brewster coefficient, B= 7.5, which is approximately 2- 5 times higher than that found in other industrial glasses.
Glass forming Germanium dioxide is optically transparent over the wide spectral range from 280- 5000nm. It is noted that good optical quality and spectral luminescence of Germanate glasses, along with the generation characteristics, make them effective material for the construction of lasers.
Below is some data for ternary Lead- Bismuth- Germanate Glasses and a data for Fluorine containing Germanate glasses:
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