Absorption and Fluorescence of Europium(III) in Aqueous Solutions

Abstract

Absorption, fluorescence, and excitation spectra of aqueous solutions of europium(III) perchlorate, chloride, nitrate, ethylenediaminetetra‐acetate, and diethylenetriaminepenta‐acetate were investigated. The latter three anions readily form complexes and were examined over a range of concentrations. The organic anions particularly, which are strong chelating agents, cause a general intensification of the spectra, shift to longer wavelengths, and increased crystal field splitting. No transfer of energy was observed from the ligand to the europium ion. Effects of changes in pH were determined and correlated with the weakly acidic nature of these chelates. Factors are discussed which lead to the hundredfold increase in some fluorescence after chelation without the benefit of energy transfer. The spectra are discussed with reference to the symmetry of europium species in solution and it is concluded that the relative intensities of forced electric dipole and magnetic dipole absorption or fluorescence bands are probably a better indication of the interaction of a europium ion with its surroundings than shifts of specific bands.