Dual mechanism of energy transfer in benzoate sensitized luminescence of Eu3+ and Tb3+

Benzoate has been studied as a sensitizer of Eu3+ and Tb3+ luminescence in aqueous and methanolic solution. In solutions with low concentrations of the lanthanide ions the mechanism is dynamic involving free benzoate triplets. At higher concentrations a switchover to a static mechanism 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 with the number of benzoate ligands.