Parameters controlling silver nanoparticle growth in sol–gel silica coatings

Silica based sol–gel coatings doped with different silver amounts have been prepared. Apart from silver concentration, other experimental parameters such as thermal densification conditions, presence of other co-dopants and the nature of the substrate have been varied in order to determine their influence on the final microstructure and properties. Characterisation of the materials prepared was carried out by optical spectroscopy (photoluminescence and absorption), secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). The study was oriented to determine the parameters governing the nucleation and growth of silver nanoparticles. The results showed that formation of silver nanoparticles was promoted when one or more of the following conditions were achieved: silver concentration in the initial sol over 5%, thermal densification under reducing atmosphere and use of pure silica substrate (in general, glass substrates without modifier ions and, therefore, with few non-bridging oxygen positions).