Investigation of fluorescence efficiency in the europium-thenoyltrifluoroacetone chelate in aqueous and ethanolic solutions by laser-induced fluorescence and photothermal spectroscopic methods

The photophysical characteristics of the europium (III)-thenoyltrifluoroacetone chelate were studied in a micellar Triton X-100 aqueous solution and in ethanol in correlation with the strong europium-sensitized fluorescence observed in these media. The properties of the chelate and the resulting ion fluorescence intensity were first compared by steady-state absorbance and fluorescence experiments. Fluorescence lifetimes, fluorescence quantum yields and energy transfer efficiencies were then investigated using time-resolved fluorescence and thermal lens measurements. In ethanol with 10(-2) M acetate buffer, the strong luminescence of europium represents only some percent of the energy absorbed by the chelate and the efficiency of energy transfer from the ligand to the ion is calculated to be 0.165. In the aqueous micellar solution, the part of radiative energy is still smaller and cannot be measured by the thermal lens method. However, the analytical sensitivity is quite comparable because the absorption spectra of the ligand and the chelate are well separate and the lifetime of the lowest excited state D-5(0) of europium(III) is made longer by the micellar environment.