Glasses Obtained by the Sol-Gel Process

Since 30 years, it is demonstrated that sol-gel processes could be a new way to synthesize materials as different as ceramics, glasses, or composites. Blinker and Scherer [12] have shown the possibilities of this technique to allow the synthesis of materials in the form of films, fibers, or bulk products. 

Gels which are originally noncrystalline may crystallize during a later heat treatment. The successful formation of a glass is the result of a competition between the phenomena which lead to densification and those which promote crystallization [14, 15]. 

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In this chapter, ways to overcome the difficulties responsible for so far obtained low efficiencies of LSCs are proposed. The proposed solutions are luminescent complexes incorporated into glasses obtained by the sol-gel process. 

Silica-based materials obtained by the sol-gel process are perhaps the most promising class of functional materials capable to meet such a grand objective. In the sol-gel process liquid precursors such as silicon alkoxides are mixed and transformed into silica via hydrolytic polycondensation at room temperature. Called soft chemitry or chimie douce, this approach to the synthesis of glasses at room temperature and pressure and in biocompatible conditions (water, neutral pH) has been pioneered by Livage and Rouxel in the 1970s, and further developed by Sanchez, Avnir, Brinker and Ozin. 

FT-IR spectra are obtained from mesoporous silica (MCM-41) dispersed in potassium bromide (KBr) pellets (the mass ratio of MCM-41 over KBr is in the 10 range). MCM-41 is obtained by a sol-gel process. It is an ordered mesoporous silica with a hexagonal array of one-dimensional pores and a narrow pore-size distribution of about four nanometers. The glass was baked at 140°C for one hour and then at 400°C for another hour to remove any carbon contaminates. 

The Raman characterization of silica gels is a by-product of researches on the sol-gel process to obtain silica glasses at low temperature from solutions of tetraalkoxysilanes. These spectra have two puzzling features that are also observed in the Raman spectrum of fused, vitreous (v) silica. Two peaks, at 490 cm-1 (called Di) and 604 cm-1 (called D2), are superimposed on the broad band at about 440 cm-1, which is the most intense signal in the spectrum of u-Si02. These two peaks are unusually... 

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