Fluorescence emission of RBL depends strongly on the polarity of the solvents and the emission maximum shifts to the red with increasing polarity of the solvent. However, RBL adsorbed at the surfaces of Y Zeolites (both HY and NaY) and ZSM-5 show two fluorescence bands at 440 nm and 580 nm where the peak at 440 nm is a new emission peak. The fluorescence intensities of both peaks were found to vary with the loading level of the probe to the catalyst surface. (c) 2005 Elsevier B.V. All rights reserved.