Characterization of sol-gel glasses with different copper concentrations treated under oxidizing and reducing conditions

Using the sol-gel process SiO2 coating and powdered samples doped with diff erent concentrations of copper were prepared. Two sets of samples were made : one was thermally treated in air atmosphere, and the other, was annealed under a CO atmosphere. Both sets of samples were characterized using X-ray diffraction, optical transmission spectroscopy, photoacoustic absorption sp ectroscopy (PAS) in the visible and near infrared region and electron param agnetic resonance (EPR). It is found that the chemical state of the copper depends on the type of treatment, amount of copper and the temperature of t he treatment. The formations of CuO or Cu colloidal particles occur after t he thermal treatments in air or in the CO atmosphere, respectively. In both cases, copper is found in the Cu2+ state in interstitial positions and pro bably substituting the Si atoms in the SiO2 matrix. The evolution of the op tical absorption spectrum as function of the Cu content is a consequence of the changes in the composition and size of the colloidal particles. The op tical and the PAS measurements are found to be complementary tools to eluci date the origin of the blue band in the absorption spectrum of these doped samples. (C) 1999 Elsevier Science Ltd, All rights reserved.