Electronic spectra of transition metal ions in gel-derived and melt-derived glasses

Abstract

The absorption spectra of 3d transition elements Cr, Mn, Fe, Co, Ni and Cu were studied in SiO 2R m O n compositions (R: a transition element), which were prepared at 500°C as coating films through the sol-gel process from a solution consisting of Si(OC 2H 5) 4, H 2O, HCl and the nitrate of a transition metal. Generally speaking, the characteristic features of the peaks corresponding to a particular valence and coordination state of an element were similar to those reported for silica glass prepared at a high temperature of 1450°C, although the concentration of the particular valence and coordination state was not equal. This indicates that the SiO 2 network similar to that prepared at high temperatures is already constructed at low temperatures around 500°C. The oxidation state of copper in glasses prepared or treated in air atmosphere was studied with melt-derived silicate and gel-derived silica glasses by measuring the optical absorption due to Cu 2+ ions and making chemical analysis. It has been shown that the redox equilibrium of copper in glass shifts towards the higher valence state as the temperature decreases in the wide temperature range from about 1550°C to 500°C and that at least a portion of the copper is present as Cu 2+ ions in SiO 2 glass prepared at low temperatures up to about 500°C.