Rare Earth Metal Containing Polymers: Energy Transfer from Uranyl to Europium Ions in Ionomers

Abstract

Various ratios of Eu and UO₂ acetates were prepared by dissolving Eu and UO₂ acetates in acetic acid and removing acetic acid in vacuum. The fluorescence intensities at 616 nm of these mixed acetates were measured under excitation at wavelength of 429 nm. Strong energy transfer from UO ²⁺₂ to Eu³⁺ was observed. This result indicated that these ions were in very close contact in this system. Various concentrations of Eu³⁺ and UO ²⁺₂ salts of polymers containing carboxyl ligands were prepared and fluorescence properties of these polymers were investigated. The polymers investigated were poly (methacrylic acid) (PMA), and copolymers of styrene-acrylic acid (PSAA) and methyl methacrylate-methacrylic acid (PMM/MA). When Eu³⁺ and UO ²⁺₂ were introduced to the polymers of PSAA and PMM/MA, very effective energy transfer from UO ²⁺₂ to Eu³⁺ was observed because of the proximity of these metal ions in ionic aggregates of these ionomers. However, the PMA-UO₂ and Eu salts did not show energy transfer even when a large excess of UO²⁺ ₂ was added to the polymer. The PMA salts are reported to have no ion aggregate structure; it is concluded that Eu³⁺ and UO ²⁺₂ ions were uniformly dispersed throughout the polymer system so that the distances between these ions were far beyond the energy transfer range.

The fluorescence lifetimes of the PMM/MA-UO ²⁺₂ and Eu³⁺ salts investigated were found to be comparable to glass studies on similar systems. Samples displayed lifetimes of 330±20 μs at 25°C.