Spectroscopic studies on Na2O–SiO2 glasses with different Ag concentration using silica obtained from wastes of a geothermal plant

A set of samples of Na2O–SiO2 glasses with different concentrations of Ag2O in the range of 3–6 wt% were prepared by melting. The silica used was obtained from purified residues supplied by a geothermic power station. The samples were annealed in air at 500 and 850 °C. They were characterized by optical (UV–VIS and IR spectroscopies) and X-ray diffraction analysis. The structural and optical studies reveal the presence of nanometric sized Ag metallic particles embedded in a porous matrix. These nanometric Ag particles produce an optical absorption band at about 400 nm, attributed to the absorption of the plasmons in the small particles. Infrared spectroscopy measurements indicate that the glasses are highly hydroscopic, which combined with the large porosity and absorbed water, produces fluctuations in the index of refraction of the SiO2 matrix. Modelling was conducted of the line shape of this band, the variations in the index of refraction, the width of the index of refraction distribution and the size of the Ag particles.