THE INCORPORATION OF RHODAMINE-B IN SILICA SOL-GEL LAYERS

The effect of the experimental conditions of the sol-gel process on the incorporation of the dye Rhodamine B in a silica layer and the consequent optical-, leaching- and light fastness-properties are reported. If at least 20 alkoxy silane groups per molecule Rhodamine B are available and if these silanes are sufficiently hydrolyzed, the dye is completely encapsulated by a three dimensional 'cage' of Si-O bonds. If this encapsulation is not the case, the dye is not properly incorporated, which results in leaching of the dye when the coating is immersed in water and in reduction of light fastness. A low acid concentration in the coating solution results in the incorporation of large amounts of Rhodamine B clusters in the silica layer. These clusters have a light absorption (maximum at 510 nm) different than incorporated monomers of Rhodamine B (maximum 560 nm).