High density, transparent and crack-free compacts of silica gel doped
with naphthazarin, quinizarin and rhodamine 6G, were produced by sol-g
el synthesis with high pressure at room temperature. Compacts are very
stable, being resistent to polishing and leaching by ethanol and acet
one. They show optical properties, as absorption and fluorescence, sim
ilar to those at dilute solutions, indicating that the dyes are disper
sed in the silica matrix as individual molecules. Heat treatment to 15
0 degrees C for 1 h led to almost no degradation. (C) 1997 Elsevier Sc
ience B.V.