Chemical and sol-gel processing of tellurite glasses for optoelectronics

Recent developments in the application of sol-gel processing technology for tellurite glass systems are reviewed and reported. The processing of telurite glasses via sol-gel entails some difficulties, mainly due to the anomalously high reactivity of Te(IV) alkoxides toward hydrolysis. Although conventional approaches to steric stabilisation of the alkoxides is not successful for these compounds, various successful approaches have been developed which allow the fabrication of transparent films from these precursors. In particular, diol complexation, chemical liberation of water from esterification processes and peptisation methods have been demonstrated. Other successful approaches involve the use of Te(VI) alkoxides and acids as precursors, with TeO₂ based glasses being formed via TeO₃ intermediates which liberate oxygen during heat treatment. One drawback with all these methods is the inherent thermal instability of the sol-gel derived material, which leads to both the liberation of free tellurium and devitrification of the glass on heat treatment. However this problem is less significant when Te(VI) precursors are used. The fabrication of multicomponent tellurite glasses by sol-gel approaches is very successful. Systems such as TeO₂-TiO₂ and TeO₂-PbO-TiO₂ have been successfully fabricated, and exhibit much greater resistance to devitrification allowing fully dense, transparent glasses to be produced.