5f state interaction with inner coordination sphere ligands: Es 3+ ion fluorescence in aqueous and organic phases

Abstract

The interaction between the 5f electron states of the Es 3+ ion and coordinated ligands in solution was probed using laser-induced fluorescence. The aquo-Es 3+ ion was observed to fluoresce from its first excited J = 5 state in a broad band peaking at 9260 cm −1. The observed fluorescence lifetimes were 1.05 us and 2.78 μs in H 2O and D 2O (minimum isotopic purity, 99 at.% D) respectively. The non-radiative decay rates derived from the lifetime data are compared with previously reported data for hydrated Cm 3+, Sm 3+, Eu 3+, Tb 3+ and Dy 3+ ions. The 5f actinide states exhibit substantially greater non-radiative decay rates than do lanthanide 4f states with a similar energy gap. This provides evidence that actinide 5f electrons interact more strongly with their inner coordination sphere than do lanthanide ion 4f electrons. The fluorescence lifetime of Es 3+ complexed with 1 formal (1g formula weight (1 mol) dissolved in sufficient solvent to give 1 dm 3+ of solution) di(2-ethylhexyl)orthophosphoric acid in n-heptane was 2.34 μs.