Energy transfer from the singlet levels of diketones and dyes to lanthanide ions in nanoparticles consisting of their diketonate complexes
The energy transfer from the S1 levels of p-phenylbenzoyltrifluoroacetone (PhBTA) and dyes to different Ln3+ ions is studied in nanoparticles (NPs) composed of complexes of this diketone with Ln3+ and 1,10-phenanthroline (phen) and doped with dye molecules. The quenching rate constants in the NPs consisting from complexes of Pr3+, Nd3+, Sm3+, Eu3+, Ho3+, Er3+, and Tm3+ are determined from the data on the quenching of sensitized (cofluorescence) and ordinary fluorescence of coumarin 30 (C30) and rhodamine 6G (R6G). The quenching rate constants vary from ≤5 × 1011 to 1013 s−1 for the fluorescence quenching of PhBTA by different Ln3+ ions, while the quenching of dye fluorescence occurs at rates of the order of 109 s−1. In the case of complexes with the Pr3+ ions, the fluorescence quenching of PhBTA in NPs composed of its complexes is accompanied by sensitized luminescence of Pr3+. The quenching observed is due to a nonradiative energy transfer from the S1 states of ligands and dyes to these ions. It is shown that in NPs composed of complexes with Eu3+, Yb3+, and Sm3+ the cofluorescence of C30 is quenched via the electron-transfer mechanism. The study of quenching of cofluorescence and fluorescence of dyes in NPs composed of mixed complexes of La3+ and Nd3+ (Ho3+) shows that the observed quenching of fluorescence and cofluorescence is governed mainly by the quenching of the S1 state of dyes when the Nd3+ (Ho3+) content does not exceed 5–10% and by the quenching of the S1 state of a ligand when the Nd3+ (Ho3+) content exceeds 50%. It is assumed that the high rate constant of energy transfer from the S1 level of ligands to ions Pr3+, Nd3+, Ho3+, Er3+, and Tm3+ in NPs composed of beta-diketonate complexes is caused by exchange interactions.
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