Understanding the complexation of Eu with potential ligands used for preferential separation of lanthanides and actinides in various stages of nuclear fuel cycle: A luminescence investigation.

A systematic photoluminescence based investigation was carried out to understand the complexation of Eu with different ligands (TBP: tri-n-butyl phosphate, DHOA: di-n-hexyl octanamide, Cyanex 923: tri-n-alkyl phosphine oxide and Cyanex 272: Bis (2,4,4 trimethyl) pentyl phosphinic acid) used for preferential separation of lanthanides and actinides in various stages of nuclear fuel cycle. In case of TBP and DHOA complexes, 3 ligand molecules coordinated in monodentate fashion and 3 nitrate ion in bidentate fashion to Eu to satisfy the 9 coordination of Eu. In case of Cyanex 923 and Cyanex 272 complexes, 3 ligand molecules, 3 nitrate ion and 3 water molecules coordinated to Eu in monodentate fashion. The Eu complexes of TBP and DHOA were found to have D local symmetry while that for Cyanex 923 and Cyanex 272 were C. Judd-Ofelt analysis of these systems revealed that the covalency of EuO bond followed the trend DHOA>TBP>Cyanex 272>Cyanex 923. Different photophysical properties like radiative and non-radiative life time, branching ratio for different transitions, magnetic and electric dipole moment transition probabilities and quantum efficiency were also evaluated and compared for these systems. The magnetic dipole transition probability was found to be almost independent of ligand field perturbation while electric dipole transition probability for D-F transition was found to be hypersensitive with ligand field with a trend DHOA>TBP>Cyanex 272>Cyanex 923.