Quantum yield measurements by thermal lens in highly absorbing samples: The case of highly doped rhodamine B organic/silica xerogels

In this work, rhodamine B-doped GPTS/TEOS-derived organic/silica monolithic xerogels were prepared by the predoping sol-gel process. Thermal lens method was applied to determine thermo-optical properties of the samples. Since the samples present a high optical absorption coefficient, the high absorption theoretical TL model was introduced. Thermal diffusivities, optical absorption coefficients, and fluorescence quantum yield values were determined for samples with different rhodamine B (RhB) concentrations, from ${10}^{\ensuremath{-}5}$ to ${10}^{\ensuremath{-}2}$ M. The dye-doped organic/silica xerogels present a high fluorescence quantum yield (up to 90%), maintaining the value over 50% until a concentration of $\ensuremath{\sim}1.6$ mM. To the best of our knowledge, RhB-doped transparent monoliths with a high fluorescence quantum yield with the highest RhB concentration reported in a solid hybrid matrix were obtained.