Interaction of Eu3+ with N,N,N',N'-tetraoctyl diglycolamide: a time resolved luminescence spectroscopy study

N,N,N',N'-tetraoctyl diglycolamide (TODGA) has been identified as one of the promising extractants for the partitioning of minor actinides from high-level nuclear waste solutions. Solvent extraction studies have shown that stoichiometry of the extracted species of Eu(3+) with TODGA depend on the nature of diluent. Time resolved luminescence spectroscopy (TRLS) has been employed to investigate the complexation of Eu(3+) with TODGA under different experimental conditions. The effects of different experimental parameters such as aqueous phase acidity, nature of diluent, and TODGA concentration on the luminescence lifetime of Eu(3+) ions have been investigated. The lifetime measurements of the complexed fraction of Eu(3+) with TODGA suggested the absence of water molecules in the inner coordination sphere of the metal ion in different solvents. In ethanol-water (60/40%) mixture, the complexation of Eu(3+) with TODGA under varying ligand-to-metal ratios suggested the formation of 1:1, 1:2, and 1:3 species, viz., Eu(TODGA)(3+), Eu(TODGA)(2)(3+), and Eu(TODGA)(3)(3+), respectively. The conditional stability constants logbeta(1), logbeta(2), and logbeta(3) were calculated as 6.1+/-0.5, 10.8+/-0.7, and 14.3+/-0.6, respectively. The nature of diluent did not influence the luminescence spectra of Eu(3+) in the presence of TODGA.