Phodamine B(RhB) was embedded in a matrix of silica gel glass by the sol gel method.Absorption and photoluminescence spectra were obtained.We found that the degree of aggregation decreases for the SiO 2 may be regarded as a hydroxylic,relatively polar environment,less polar than water although controversy still exists on the role of water in causing aggregation.Photoluminescence red shift was observed which may be interpreted as reflecting a decrease in the dipole moment of the exited molecule.