Intramolecular Energy Transfer The Fluorescence of Complexes of Europium

The characteristic line fluorescence of trivalent europium is excited in certain organoeuropium compounds by irradiation with light absorbed only by the organic part of the compound. The efficiency of excitation varies greatly with the nature of the compound, temperature, and solvent. Under optimum conditions, i.e., solution of a covalent compound at liquid-air temperature, almost unit efficiency has been obtained. The decay time of the fluorescence is independent of quenching; quenching prevents excitation of the europium ion. There seems to be a steady gradation of efficiency of transfer from covalent to ionic compounds.