OPTICAL SPECTROSCOPY OF HYBRID SOL-GEL COATINGS DOPED WITH NOBLE-METALS

Sol-gel coatings in the xM.(100 - x)SiO2 system, (M = Cu, Ag and Au) ( x = 0.1-10 mol%), are deposited on soda lime glass slides by using sil icon tetramethoxide Si(OCH3)(4)) and methyltriethoxysilane (SiCH3[OCH2 CH3](3)) as silica precursors. Anhydrous CuCl, CuCl2. 2H(2)O, Cu(NO3)( 2). 3H(2)O, CuSO4. 5H(2)O, AgNO3 and HAuCl4. 3H(2)O are used as copper , silver and gold sources. Coatings with thicknesses ranging from 100 to 900 nm are deposited on the substrates by dip-coating and subsequen tly densified at 500 degrees C for 1 h in air. Spectroscopic studies o f the coatings as a function of the thicknesses and the metal concentr ation are carried out by photoluminescence (PL) and optical absorption (OA). In addition, direct observations of some gold coatings were per formed by transmission electron microscopy (TEM). Results indicate tha t for silver and copper containing coatings the excitation and emissio n spectra arise from electronic transitions in Ag+ and Cu+ ions and no significant absorption bands due to colloidal precipitation are obser ved. Gold containing coatings show purple coloration due to an absorpt ion peaking in the 520-560 nm range, which is characteristic of gold c olloids. The presence of these colloids is confirmed by TEM observatio ns.