SiO2-coatings on glass containing copper colloids using the sol-gel-technique

A sol-gel method for the preparation of transparent copper nano particle-containing SiO2 coatings on glass has been developed. The sol is synthesised from alkoxysilanes and tetra ethyl orthosilicate with copper ammine complexes, prepared from Cu²+ salts and amino alkoxy silames. Glass substrates are coated by dipping and layers up to 1 µm in thickness are obtained after thermal densification at temperatures between 200°-500°C. The Cu colloid formation can be achieved using a reducing atmosphere during densification. Thus reddish-brown coloured coatings on glass with optical densities between 0.5 and 2 are obtained. Under ambient air the colour turns from reddish-brown to dark green. This process is reversible and by re-heating under reducing conditions the reddish-brown colour can be re-establised. UV-VIS absorbance measurements and structural investigations by WAXS, TEM, ESCA and SNMS show that the green colour is due to an oxide layer at the colloidal interface