Studies in sol-gel glasses with incorporation of Cu and Fe, using PAS, X-ray diffraction and EPR

SiO2 Glasses with incorporation of either Cu or Fe were prepared by the sol -gel process and annealed in air at temperatures within the range of 100 to 500 degreesC. The samples were characterized using Visible Photoacoustic A bsorption Spectroscopy (PAS), X-ray powder diffraction and Electron Paramag netic Resonance (EPR). Under the annealing both systems show significant ch anges in composition, producing an evolution in the optical absorption spec tra. In both systems, the formation of the metal oxide particles is observe d after annealing at or above 300 degreesC. The optical and EPR spectra are interpreted in terms of the coordination of the metal ions using the ligan d field theory. It is observed that the color of the samples has strong cha nge with both the type of metal incorporated and with the annealing tempera ture.