Glass forming ability, structure and spectroscopic properties of silica-free calcium aluminate based glasses.

Abstract

Calcium aluminate based glasses are interesting because of their unusual optical properties and the fact that they do not contain any traditional glass forming ions. A large focus of the glass literature has been concerned with the study and properties of typical glass forming ions. For this reason, comparatively little is known about the possibility of glass formation and the structure and properties in unusual systems. The present work will describe the limits of glass formation within the calcium aluminate system. The use of non-silicate based stabilizing additives will also be detailed. It has been demonstrated that certain additions to the calcium aluminate system will improve the glass formation tendency without impairing the desired optical properties. The effects of various ions and their impact on the processing and properties of the glasses will be described in the framework of traditional theories of glass formation. Additional optical properties of the calcium aluminate system have also been investigated. Using the Judd-Ofelt model, various spectroscopic properties of calcium aluminate based glasses have been calculated. The stimulated emission cross section, branching ratios, intensity parameters and transition probabilities show interesting variations with compositional manipulations. Attempts to improve the emission cross section will also be described. The structure of calcium aluminate based systems has been studied using NMR and Raman Spectroscopy. The coordination of alumina has been examined with respect to compositional changes. In addition, structural studies have been conducted on calcium aluminate glasses synthesized by the sol-gel method. This method has allowed the formation of higher alumina content glasses. The evolution of structure with heat treatment temperature was followed and a comparison between melt-derived and sol-gel prepared glasses has been made.