Concentration quenching and depolarization of rhodamine 6G in the presence of fluorescent dimers in polyvinyl alcohol films

Nonradiative energy transport in a concentrated system of rhodamine 6G in polyvinyl alcohol films is studied. Concentration changes in absorption and fluorescence spectra evidence the presence of rhodamine 6G fluorescent dimers. The results of concentration quenching and depolarization agree with the hopping theory of forward energy transport up to intermediate concentrations. At the highest concentrations, the experimental quantum yield is higher than the theoretical one and no repolarization effect is found at room temperature. These discrepancies are explained by the formation of fluorescent dimers which are imperfect traps for excitation energy. This conclusion is supported by measurements at elevated temperature.