The structure of ligands and effects of the europium luminescence excitation

Results of studies of the luminescence excitation spectra of europium compounds: β-diketonates, aromatic carboxylates, nitrates with sulfoxides are presented. The processes of transfer and degradation of the excitation energy are discussed. Alteration of the relative contribution of two inequivalent ligands to the luminescence excitation of europium β-diketonates with 1,10-phenanthroline derivatives upon modification of ligand radicals and variation of relative binding strength of ligands by metal ion was investigated. The participation of the ligand–metal charge transfer states both in degradation of the excitation energy and in enhancement of Eu3+ luminescence excitation was analyzed. Increase of intraligand charge transfer upon introduction of a ligandʹs acceptor substituent such as nitro-group, decreasing the ligand–metal charge transfer, was demonstrated. Blocking effect of methylene or oxymethylene bridges on the energy transfer from ligand to Eu3+ ion was observed. This phenomenon witnesses about the electron exchange mechanism of the interaction between the disjuncted parts of the ligand.