Fluorescence enhancement and cofluorescence in complexes of terbium(III) with trimellitic acid

The fluorescence of terbium (III) was enhanced by about three orders of magnitude in the presence of trimellitic acid (benzene-1, 2, 4-tricarboxylic acid (TLA)) in aqueous solution at pH 6. The fluorescence intensity could be greatly increased when the system of Tb3+-TLA was treated with La3+(or Gd3+) and TritonX-100. The addition of La3+(or Gd3+) enhances the fluorescence of the system by about two orders of magnitude due to cofluorescence, and the TritonX-100 micellar medium plays an important role for stabilization of the system. Both the intermolecular energy transfer mode and intramolecular energy transfer mode are responsible for the mechanism of fluorescence enhancement. In the optimum conditions, the fluorescence intensity is a linear function of Tb3+ concentration in the range of 7.8 × 10−9-3.6 × 10−6 mol/L for the system Tb3+-La3+-TLA and 1.0 × 10−8-4.7 × 10−6 mol/L for the system Tb3+-Gd3+-TLA, and the limits of detection are 4.6 × 10−10 mol/L and 6.0 × 10−10 mol/L, respectively.