Redox relaxation in a sodium borosilicate glass doped with copper and arsenic, antimony, or tin

Glasses with the nominal chemical composition 25Na2O·15B2O3·60SiO2 (mol%) doped with copper and arsenic, antimony, or tin as redox agents were studied by optical absorption spectroscopy in the temperature range from 25 to 620 °C. In general, the redox agents decrease the Cu2+-concentration in the glasses. Increasing the temperature to 620 °C resulted in a shift of the Cu2+ absorption band from 12,600 to 11,800 cm− 1. In glasses solely doped with copper or with copper and tin, the absorptivity decreased by about 5% in that temperature range. In principle, glasses doped with both copper and arsenic or antimony showed the same behaviour up to a temperature of 420 °C. For these glasses, heating to higher temperatures resulted in a minimum at around 540 to 500 °C and a subsequent strong re-increase in absorptivity. During cooling from 620 °C a steep decrease in absorptivity down to a temperature of 520 °C and after passing through a minimum a slight re-increase was observed. The Cu2+ concentration, and hence the absorptivity, after cooling depends on cooling rate (10 to 0.5 K min− 1).