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 Eu3+ with TODGA depend on the nature of diluent. Time resolved luminescence spectroscopy (TRLS) has been employed to investigate the complexation of Eu3+ 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 Eu3+ ions have been investigated. The lifetime measurements of the complexed fraction of Eu3+ 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 Eu3+ 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)23+, and Eu(TODGA)33+, respectively. The conditional stability constants log β1, log β2, and log β3 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 Eu3+ in the presence of TODGA.