Effect of thermal stabilization on the optical absorption of some transition metal ions in glass

The optical absorption of a 30Na₂O, 70SiO₂ glass containing iron, chromium or cerium has been studied after thermal stabilization at various temperatures around the transformation range of the glass. The optical absorptions due to iron(II), iron(III), cerium(III) and cerium(IV) have been found to increase with increasing stabilization temperature; the optical absorptions due to chromium(III) and chromium(VI) do not change significantly with stabilization temperature. The changes in optical absorption due to stabilization at different temperatures have been found to be reversible and reproducible. It has been argued that as the equilibrium volume of a given mass of glass increases with increasing stabilization temperature, and as the ligand field strength surrounding the transition metal ion does not increase due to this enlargement of volume while the optical absorption increases, the high temperature stabilization of a glass probably increases some local randomness of structure (creating extra distortion of the transition metal complex) and does not cause an uniform volume expansion of the glass.