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 monolith matrices produced using the sol–gel process from a tetraethylorthosilicate precursor. The effect of different solvents included in the matrix forming reaction and retained within the pore structure of the finished bulk matrix, on both the steady state and time-resolved fluorescence was monitored. The solvents were chosen both in terms of dielectric constant (ranging from 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 demonstrated that the peak fluorescence emission could be tuned by addition of solvents with different dielectric constants. The lower limit of this wavelength range was mainly determined by interaction with the host, while the upper limit related to emission from an added solvent and water mixture. An improvement of up to two times in the fluorescence yield of Nile Red, relative to the sample with no added solvent, was observed in matrices with retained solvent.