Sol-gel materials for opto(electronic) applications

Conventional glass preparation requires melting of precursors at high temperatures, rapid cooling and subsequent vitrification of the glassy material. This procedure highly restricts choice of substances which can be entrapped in the glass products. Basically only metal oxides and some inorganic salts can survive such drastic conditions avoiding thermal decomposition. Furthermore, the way in which conventional glass is produced makes thin films preparation extremely cumbersome and the only method of preparation of porous classical glasses requires etching or partial dissolving (e.g. Vycor® glass). On the other hand glass and glassy materials possess several useful features for e.g. optical applications such as transparency, homogeneity, mechanical sturdiness, high refractive index etc. An alternative approach to glass and glass-like materials production is offered by the sol-gel technology. The process itself is known for more than a century, but it has gained a new importance in the last two decades after pioneering results of Dislich. He and other researchers improved the chemistry of the process so much that it is now possible to obtain samples in days (or even hours — in case of thin films) rather than months (or years) like in the case of the early samples. The sol-gel technique is based on hydrolysis of liquid precursors and formation of colloidal sols. The precursors are usually organosilicates (e.g. TEOS — tetraethoxysilane) giving silicate sol-gel materials. However, the method is not restricted to the silica compounds — for example precursors based on Ti, Zr, V etc.