DUAL MECHANISM OF ENERGY-TRANSFER IN BENZOATE SENSITIZED LUMINESCENCEOF EU3+ AND TB3+

Benzoate has been studied as a sensitizer of Eu3+ and Tb3+ luminescenc e in aqueous and methanolic solution. In solutions with low concentrat ions of the lanthanide ions the mechanism is dynamic involving free be nzoate triplets. At higher concentrations a switchover to a static mec hanism involving complexed benzoate occurs. In the case of EU(3+) the dynamic sensitization is 3 times as efficient as the static one, which is explained by CT-quenching of singlet benzoate in the complex. The emission quantum yield of Eu3+ and Tb3+ benzoate complexes increases w ith the number of benzoate ligands.