CALCULATION OF THE LIGAND-LANTHANIDE ION ENERGY-TRANSFER RATE IN COORDINATION-COMPOUNDS - CONTRIBUTIONS OF EXCHANGE INTERACTIONS

Recently, one of us (O.L.M.) developed a theoretical approach to the e nergy transfer process between a ligand and a lanthanide ion in lumine scent compounds. This approach takes into account the direct Coulomb i nteraction only. Here we present further calculations which also inclu de the exchange Coulomb interaction (isotropic and anisotropic). The s election rules on the total angular momentum, J, of the lanthanide 4f states, derived from each interaction are different. They are in fact complementary. We discuss the case of energy transfer to the D-5(1) ma nifold of the Eu3+ ion, which is forbidden when only the direct Coulom b interaction is considered but becomes allowed through the exchange i nteraction. In this case numerical estimates show that, depending on r esonance conditions and the nature of the ligand donor state, the tran sfer rate may assume very high values. It is also emphasised that, acc ording to the present approach, energy transfer to the D-5(0) level of the Eu3+ ion is forbidden by both mechanisms, provided J-mixing betwe en the F-7(0) and F-7(2) manifolds is neglected.