The effect of the nature of retained solvent on the fluorescence of Nile Red incorporated in sol-gel-derived matrices

The environmentally sensitive dye Nile Red was incorporated into glass mono lith matrices produced using the sol-gel process from a tetraethylorthosili cate precursor. The effect of different solvents included in the matrix for ming reaction and retained within the pore structure of the finished bulk m atrix, on both the steady state and time-resolved fluorescence was monitore d. The solvents were chosen both in terms of dielectric constant (ranging f rom 2.4 to 47), viscosity and the fact that some have an important role in alleviating stresses during the drying stage of the sol-gel process. It was found that the dye was solvated within the matrix pore structure and demon strated that the peak fluorescence emission could be tuned by addition of s olvents with different dielectric constants. The lower limit of this wavele ngth range was mainly determined by interaction with the host, while the up per limit related to emission from an added solvent and water mixture. An i mprovement of up to two times in the fluorescence yield of Nile Red, relati ve to the sample with no added solvent, was observed in matrices with retai ned solvent. (C) 2001 Elsevier Science B.V. All rights reserved.