Many-body nonradiative energy transfer in a crystalline europium (III) EDTA complex

A pulsed, tunable dye laser has been used to excite the 7F0→ 5D0 electronic transition of the europium (III) ion in single crystals of Na[Eu(EDTA)(H2O)4]doped with varying concentrations of gadolinium. since this electronic transition cannot be split by crystal fields exerted by the ligands surrounding the metal ion, the noticeably broadened and asymmetric excitation spectra observed for this electronic transition at high europium concentrations have been ascribed to interactions between excited europium (III) ions and adjacent, unexcited europium (III) ions, resulting in energy transfer between ions. The lifetimes of these Na[Eu(EDTA)(H2O)4]crystals have been measured and a linear relationship was found between the energy transfer probability (Pda) and the square of the europium (III) concentration. The many-body nonradiative energy transfer process proposed by Fong and Diestler has been used to interpret the observed lifetime data, and the corresponding mechanism has been verified to be due to an electric dipole-dipole interaction. This model is consistent with one excited europium (III) ion transferring energy to two adjacent, unexcited europium (III) ions. As expected, the nonradiative energy transfer disappears if the % europium is decreased in the single crystal by doping small amounts of europium (< 0.3%) into a gadolinium matrix. The lifetime, excitation and emission spectra of a series of complexes containing different percentages of europium will be discussed in terms of nonradiative energy transfer theory.