Fluorescence enhancement and cofluorescence in complexes of terbium, dysprosium and europium with trimesic acid

The fluorescence of terbium, dysprosium and europium was enhanced by about two to three orders of magnitude when they were excited in the presence of trimesic acid in aqueous solutions at pH 6. The fluorescence was enhanced by a further order of magnitude when these lanthanide-trimesate complexes were treated with trioctylphosphine oxide (TOPO) and Triton X-100. The enhancement following the addition of TOPO is strongly pH dependent. An enhancement in the fluorescence of these rare earths with the carboxylate ligand is observed in the presence of ions such as La3+ and Gd3+, due to cofluorescence. The addition of La or Gd enhances the fluorescence of the lanthanide-trimesic acid complexes by almost two orders of magnitude, leading to detection limits in the sub-ng ml-1 range for these rare earths