Transition metal ions in silicate melts. Part 2. Iron in sodium silicate glasses

Optical absorption, luminescence, and Raman spectra were measured for sodium silicate glasses melted in air, containing about 85% Fe(III) and 15% Fe(II). Luminescence intensities for individual samples were compared. Three d-d bands in the optical absorption spectrum due to Fe(III) at about 26,000, 24,000, and 23,000 cm/sup -1/ were assigned to the /sup 4/E(D), /sup 4/T/sub 2/(D) and /sup 4/A/sub 1//sup 4/E(G) levels of the d/sup 5/ configuration. Another very weak band arose from the /sup 4/T/sub 2/(G) level. Luminescence spectra indicated an unobserved band at around 16,200 cm/sup -1/ due to the /sup 4/T/sub 1/(G) level. Raman and luminescence spectra both showed that two distinct fourfold coordinated environments for Fe(III) existed in the glasses. In glasses of low sodium content, Fe(III) substitutes for Si with four bridging oxygens, producing Raman bands at 980 cm/sup -1/ and luminescence at 14,600 cm/sup -1/. In high sodium glasses, the Raman bonds occurred at 890 cm/sup -1/ and luminescence appeared at 16,200 cm/sup -1/. It is argued that this may be a tetrahedral iron complex in the glass. Ferrous iron appeared to occupy a sixfold coordinated site the size of which decreased with increasing sodium concentration.