Concentration-Dependent Fluorescence Properties of Rhodamine 6G in Titanium Dioxide and Silicon Dioxide Nanolayers

Thin films of rhodamine 6G in titanium dioxide (Rh6G/TiO2) and silicon dioxide (Rh6G/SiO2) were synthesized using the sol-gel method. We explored two lcinds of matrices as hosts for rhodamine 6G (Rh6G) at different concentrations of the dye. The pronounced effect of the dye concentration on the absorption and fluorescence spectra as well as on time-resolved fluorescence spectra was found. In particular, it was found that the aggregation of the guest dye is significantly weaker in the Rh6G/TiO2 nanolayer. The absence of an isosbestic point in absorption spectra in a silica matrix suggests the formation of higher order aggregates, whereas the changes of absorption profile in Rh6G/TiO2 matrix indicate the formation of dimers. Rh6G aggregates are strongly fluorescent in Rh6G/TiO2 nanolayer, which can be seen from time-resolved and steady-state emission spectra. For Rh6G/SiO2 nanolayers these changes are much less pronounced and concern mostly the red shift of the fluorescence maximum.