Extinction coefficient of the cupric ion in soda-lime-silica glasses

Abstract

It is shown that if an ion dissolved in a glass obeys Beer's and Lambert's laws and shows a regular dependence of equilibrium constant on temperature, its extinction coefficient can be determined in two different ways from only absorbance measurements and knowledge of the total concentration of the oxide. This may be done by bringing melts to equilibrium at one temperature but two different oxygen partial pressures or by making melts at one partial pressure but three different temperatures. A chemical estimation of the fraction of the oxide in either valence state is not needed. These methods are here used to study the composition dependence of extinction coefficient of the cupric ion in five soda-lime-silica glasses, brought to equilibrium with air, with compositions covering the ranges (in mol%) 14.7 to 22.0 Na2O, 12.0 to 20.0 CaO, 66.0 to 73.3 SiO2. Values of ε(Cu2+) range from 20.8 to 25.8 l mor^-1 cm^-1 and show that both extinction coefficient and [Cu+]/[Cu2+] ratio increase with increasing basicity.