Influence of oxygen incorporation on infrared transmission of ternary Ge-Sb-Se chalcogenide glass in the compositional range for use in infrared-imaging applications

Optical transmission window of ternary Ge-Sb-Se glass extends up to ∼15 μm, thus being transparent across the long-wavelength infrared (LWIR; 8–12 μm) range. Along with its superior thermal stability as to the precision glass molding (PGM) process, this Ge-Sb-Se glass is most well-known as the material of choice for LWIR-imaging lens applications. Presence of oxygen atoms on the surface and/or in the interior of LWIR-transmitting chalcogenide glass needs to be allowed to a tolerable amount; otherwise, its LWIR transmittance is deteriorated due to the vibrational excitations of oxygen-related bonds. In this study, we take into consideration ternary Ge-Sb-Se glasses as an exemplary case to get a clear grasp on correlations between oxygen incorporation and LWIR transmittance of chalcogenide glass: Surface oxidation turns out to be insignificant to the LWIR transmittance, but presence of oxygen inside the glass is reconfirmed to exert a strong influence. It is verified that the oxygen-related absorption peak located at ∼800 cm^-1 is mainly dominated by Ge–O vibrations; however, its position tends to redshift with increasing Sb content, implying indirect involvement of Sb atoms. Also verified is that the surface of Sb powders chosen as a starting material is more vulnerable to oxidation than the surface of Ge powders. This observation makes it reasonable to assume that Ge–O bonds are preferentially formed, at the expense of Sb–O bonds, during melting of the starting materials.