Comparison of the fluorescence behaviour of rhodamine 6G in bulk and thin film tetraethylorthosilicate derived sol-gel matrices

A comparison has been made between thin film and bulk sol-gel derived matri ces produced from the same reaction mixture. This was carried out by the in corporation of various concentrations of rhodamine 6G and monitoring the dy es fluorescence behaviour using both steady state and time-resolved fluores cence spectroscopy. Measurements were performed on matrices, which were con sidered to be in a stable condition and unlikely to undergo any further maj or structural changes. In the thin film matrices the fluorescence decay was non-exponential and appeared to relate to different environments for the d ye molecules. This was supported by anisotropy measurements that imply that dye is present adsorbed to the silica matrix as well as solvated within so me of the pores. In the bulk matrices the time-resolved fluorescence decay was monoexponential (decay time 4.34 ns) and on increasing the rhodamine 6G concentration the main phenomenon observed was that of self-absorption. Ev idence was found for the presence of solvent within the bulk matrix and tim e-resolved fluorescence anisotropy indicated the existence of two main envi ronments of differing viscosity (7 and 195 mPa s), which can relate to diff erent pore sizes. Measurements of energy transfer from rhodamine 6G to mala chite green showed a much greater than expected efficiency at low acceptor concentrations. This is attributed to confinement of the dye within the por e and reflects a distribution of pore sizes. (C) 1999 Elsevier Science S.A. All rights reserved.