Raman Study of the gel-to-glass conversion of fluorine-doped silica.

Raman spectroscopy was used to investigate the structural and chemical changes of F-doped silica gels as a function of sintering temperature and atmosphere. The results show that, regardless of the initial gelation conditions, most Si-F groups, that are initially present in the dried gel, are lost from the gel after heating at 1000C. Since Si-F groups are eliminated by reaction with Si-OH groups, higher concentrations of fluorine can be retained when SiOH groups are removed by adding Cl sub 2 to the sintering atmosphere. For the glasses, that are formed after heating at 1400C, the highest F concentrations are found when SiF sub 4 is present during densification.