Fluorescence Quenching and Luminescence Sensitization in Complexes of Tb~(3+) and Eu~(3+) with Humic Substances

摘要

Intrinsic fluorescence quenching of humic substances (HS) and the sensitization of Ln~(3+) luminescence (Ln~(3+) = Tb~(3+),Eu~(3+)) in HS complexes were investigated. Both measurements yielded complementary information on the complexation of metals by HS. Large differences between fulvic acids (FA) and humic acids (HA) were found. From time-resolved luminescence measurements it is concluded that a combination of energy transfer and energy back transfer between HS and Ln~(3+) is responsible forthe observed luminescence decay characteristics. In the case of Eu~(3+),an additional participation of charge-transfer states is suggested. A new concept forthe evaluation of the sensitized luminescence decays of Ln~(3+) was adapted.