Preparação e caracterização de vidros de fosfato de tungstênio contendo nanopartículas metálicas de prata, ouro e platina

Abstract

Glass samples were prepared by the melt-quenching method using sodium polyphosphate and tungsten oxide with WO3 contents varying from 30 mole% to 50 mole%. Oxidizing agents (CeO2 and Sb2O3) have been used to avoid tungsten reduction and produce glass samples with higher transparency in the visible. These glasses were doped with noble metals using salts precursors Au2O3, PtCl4 and AgNO3. Transparent and homogeneous glasses containing 0,1 mole% of each metallic salt were successfully obtained. UV-visible spectra confirmed transparency of the doped and undoped glasses containing oxidizing agents CeO2 and Sb2O3. Raman spectroscopy was useful to access structural parameters of the glass network, which is built-up of PO4 and WO6 units, with WO6 clusters in the most WO3 concentrated samples. The doped glasses (Ag, Au and Pt) heat treated above the glass transition temperature exhibit an intense absorption band in the visible with a specific absorption maximum for each doped sample which has been attributed to surface plasmon resonance of metallic nanoparticles precipitated inside the glass network. DSC together with X-ray diffraction results allowed proposing a crystallization mechanism in which metallic nanoparticles are able to induce precipitation of monoclinic WO3 and further precipitation of tungsten sodium phosphate NaWO2PO4. Finally, Raman investigations showed that the gold-doped sample exhibits a different Raman spectrum when compared with the other doped and undoped samples, suggesting a possible SERS effect which can be related with a resonance between the laser wavelength (633nm) and the plasmon resonance absorption band in this gold-doped sample.