Energy transfer between lanthanide ions in dinuclear complexes

Abstract

Energy-transfer rate constants between two trivalent lanthanide ions have been determined at a short and fixed distance of ca. 4 Å, by using mixed dimers of tris(acetylacetonato)lanthanide complex, Ln(acac)₃, formed in chloroform. The energy-transfer rate constants were obtained by measuring the luminescence decay constant of an energy-donor ion in the mixed dimer. The lanthanide ions used as energy donors and/or energy acceptors were Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺ Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Yb³⁺. The energy-transfer rate constant, 10⁴–10⁷ s^–1, could be correlated with the gap in electronic transition energies between the donor and the acceptor. The values were one or two orders of magnitude larger than those estimated from the distance dependence in a known equation based on dipole–quadrupole interaction and than those calculated in terms of the Förster model. It is proposed that, for energy transfer at short distances the electron-exchange interaction is predominant over the dipole–dipole or dipole–quadrupole interactions.