Ligand-sensitized fluorescence of Eu3+ using naphthalene carboxylic acids as ligands

Fluorescence enhancement of Eu3+ in its complexes with 1-naphthoic acid (NA) and 2,6-naphthalenedicarboxylic acid (NDA) has been studied. These ligands enhance the fluorescence of Eu3+ by about two to three orders of magnitude. The fluorescence of Eu3+ in these complexes is further enhanced by more than two orders of magnitude when these complexes are treated with trioctylphosphineoxide (TOPO) and a surfactant. The enhancement due to TOPO is accompanied by an increase in the lifetimes of Eu3+ emission in these complexes, compared with the emission in uncomplexed Eu3+. The fluorescence of Eu3+ in the Eu3+–NDA–TOPO/surfactant complex is further enhanced by the addition of Tb3+, leading to the possibility of detecting Eu3+ at levels of 10−10 M. This ligand gives one of the best limits of detection for Eu3+ of all the carboxylic acid ligands that we have studied thus far.