Fe3+ doped SiO2 nanostructured gel-glasses: Structural, optical and magnetic properties

Transparent crack-free and bubble-free Fe3+ doped SiO2 nanostructured gel-glasses were obtained by the sol–gel process. The process involves the hydrolysis and condensation of an appropriate molar ratio of tetraethoxysilane (TEOS), absolute ethanol, nitric acid and ferric nitrate, followed by stepwise annealing at temperatures ranging from 110 °C to 1000 °C. The structural variation of the gel-glasses and their influence on physical properties during annealing has been studied. It has been observed that monolithicity and chemical environment around Fe3+ in the gel-glasses are strongly dependent on the annealing temperatures. The colour of gel-glass samples is different for different annealing temperatures, mainly due to the different co-ordination state of Fe3+ and the generation of Fe2O3 colloids of size 20–60 nm in the silica matrix. The annealing process facilitates the tuning of the UV–visible transmission cut-off edge in high optical quality Fe3+ doped silica gel-glasses. A marked difference in the magnetic properties of these glasses is also observed with annealing temperatures.