The Effect of Oxide Impurities on Infrared Absorption Spectra of Chalcogenide Glasses

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Abstract
Hereunder is presented the report on the investigation of the infrared absorption spectra in a variety of chalcogenide glasses. The absorption band at about 12.5-12.7μ observed for As-S glasses prepared by the evaporation and/or distillation methods (Refs. 12 and 14) was formally attributed to the vibration of As=S bond in AsS2.5 component and/or to the AsS component included in a glass (Ref. 13). The corrected assignment of the band in this region is given by the present investigation to be due to the vibration of As-O bond. On the basis of this assignment the oxidation process in the above evaporation and distillation procedures is suggested for the preparation of As-S glasses. Two absorption bands near 15 and 21μ for As-S glasses shifted respectively from 15.2 to 14.5μ and from 20.5 to 21.1μ as the arsenic content decreased, provided that the thickness of the glasses was controlled within 0.1-0.2mm. Correspondingly the relative intensity of the former band decreased and that of the latter increased. A possible structure coincident with these results is the formation of AsS2.5 component including the dative As→S bond in glasses in the AsS1.5-S system. The following absorption bands are attributed to the contamination with oxygen: about 12.6 and 16μ bands in As-Se and As-Se-Te glasses, 11.2-11.4 and 13.6-13.7μ bands in Ge-As-Te glasses, 10.2-10.4 and 13.9-14.5μ bands in Si-As-Te glasses. These bands, except the bands due to the Si-O bond in Si-As-Te glasses, can be eliminated by the melting procedure in carbon-coated silica glass ampule. The oxide-free As-Se, As-Se-Te and Ge-As-Te glasses show good transparency up to about 20μ, whereas As-S glasses up to about 13μ; the uniform transmission is limited by about 10μ for Si-As-Te glasses contaminated with oxygen because the reduction of SiO2 by carbon is thermodynamically impossible.

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