Ultrafast Transient Absorption Study of the Nature of Interaction between Oppositely Charged Photoexcited CdTe Quantum Dots and Cresyl Violet

Abstract

Understanding the dynamics of exciton quenching of the quantum dots (QDs) is of great importance considering the fact that the applications of these substances are based mainly on luminescence. In this work, we have studied exciton quenching of the CdTe QDs by cresyl violet (CV) employing steady-state and time-resolved absorption and emission techniques. Efficient luminescence quenching of these QDs is observed in the presence of CV. Interestingly, despite an excellent overlap of the absorption and emission spectra of CV and QDs, respectively, the emission quenching of the QDs is not accompanied by an increase in the steady-state fluorescence intensity of CV or a rise in its fluorescence time profile that can be considered as evidence for the Förster resonance energy transfer process. The time-resolved fluorescence measurements suggest that the quenching is partially due to static interaction of the two species. The transient absorption studies in the 0-100 ps time scale show that recovery of the 1S exciton bleach of the QDs is much faster in the presence of CV when compared with that in its absence, indicating that ultrafast photoinduced electron transfer from the conduction band of the QDs to CV is responsible for the emission quenching of the former. The recombination of the charge-separated species is found to occur in ∼2 ps.