Optical spectroscopy of arsenic- and silver-containing sol-gel coatings

Sol-gel silica coatings doped with 1 mol% silver and/or 1 mol% arsenic oxid e have been investigated by photoluminescence (PL) and optical absorption ( OA) spectroscopy. The presence of Ag+ ions in the silica host has been moni tored by recording a luminescence peak located between 320 and 330 nm upon excitation with 228 nm light, whereas the formation of small particles of m etallic silver has been assessed by recording the absorption band centred a t about 405 nm. The luminescence peak has been related to the d(10) <-> d(9 ) s parity-forbidden transitions in Ag+, which are partially allowed by odd -phonon assistance. On the other hand, the absorption peak at about 405 nm arises from the well known surface-plasmon resonance of silver particles. C oating densification under various atmospheres gives rise to significant ef fects on the PL and OA spectra. Results indicate that, after coating densif ication in air, most of the silver appears as Ag+ ions, in contrast to coat ing densification under a 90% N-2-10% H-2 atmosphere, which favours the for mation of small particles of metallic silver. The presence of arsenic oxide in the silver coatings densified in air has been found to improve the stab ilization of Ag+ ions, so that partially prevents the formation of colloida l silver under reducing atmospheres.