Localized states in germanate glasses. Ultraviolet absorption tail of crystalline and glassy germanium dioxide and alkali germanate

• Published in: Journal of non-crystalline solids 1995-07, Vol.188 (1), p.125-129
• Main Authors: Trukhin, Anatoly N, Pēteris, Kūlis
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other nonmetallic inorganics; Other nonmetals; Physics; Visible and ultraviolet spectra
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/0022-3093(95)00094-1

The optical absorption of crystalline and glassy germanate were measured with a double-beam instrument. Pure GeO 2, Li 2GeO 3 crystal, pure GeO 2, sodium germanate and lanthanum germanate glasses were studied. Glass samples were prepared by melting and some by evaporation during melting. Melting conditions were normal and oxidizing. Intrinsic absorption tails of a GeO 2 crystal with a structure of α-quartz and in a Li 2GeO 3 crystal are situated at 6 eV. Two absorption thresholds were observed in a GeO 2 glass: one is situated at 6 ± 0.2 eV, the other at 4.5 ± 0.2 eV. The intensity of the latter increases in sodium germanate glasses and corresponds to the intrinsic absorption threshold of a tetragonal GeO 2 crystal. This threshold is known from the literature. The absorption spectra and their thermal dependences are well approximated by the Urbach rule in two forms. The threshold at 6 eV in all the materials studied obeys the Urbach-Toyozawa rule. The threshold at 4.5 eV agrees with the so called ‘glass’ type rule.