Influence of platinum, antimony and iron ions on coloration of alkali-borosilicate optical glass

We studied influence of platinum, antimony and iron ions on the coloration of alkali-borosilicate glass. The optical transmittances of glass specimens with and without antimony were compared, and the cause of absorption in antimony-free glass was studied. It was found in antimony-free glass that a small amount of dissolved Pt2+ on the ppm order causes strong absorption at approximately 360 nm resulting in a yellowish color. This absorption was not observed in the specimens melted at temperatures below 1150 °C, or in the colorless specimens containing antimony or iron. It was indicated, in the colorless specimens that platinum exist as Pt4+, the absorption of which occurs in the UV region. The oxidation state of platinum ions was strongly affected by melting temperature or coexisting multivalent ions such as antimony or iron ions, which act as an oxidant of platinum ions. Keeping the melting temperature low and employing appropriate oxidant ions are effective means of designing colorless antimony-free optical glass.

► Pt2+on the ppm order causes a strong absorption at 360 nm in Sb-free glass.
► In Sb-containing glass, Pt2+ is oxidized to Pt4+ which absorbs in UV region.
► The valence of Pt is dominated by coexisting Sb or Fe ions, or melting temperature.
► It is essential to control Pt ions valence for obtaining a colorless Sb-free glass.