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 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 of 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 (FRET) 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 timescale show that recovery of the 1S exciton bleach of the QDs is much faster in presence of CV when compared with that in its absence indicating that ultrafast photo-induced electron transfer (PET) 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 about 2 ps.

An Ultrafast Transient Absorption Study of Charge Separation and Recombination Dynamics in CdSe QDs and Methyl Viologen: Dependence on Surface Stoichiometry

“…The broad positive absorption (580‐650 nm) observed in our case on addition of MV +2 (Figure ) can be attributed to MV +• species based on the literature . The electron transfer between CdSe QDs and MV +2 is further substantiated from the QDs 1S bleach recovery, considering the fact that 1S bleach of QDs is sensitive to electrons ,,. Figure shows the comparison of 1S bleach recovery of QDs in the absence and presence of MV +2 in 100 ps time window.…”

Role of Emissive and Non‐Emissive Complex Formations in Photoinduced Electron Transfer Reaction of CdTe Quantum Dots

“…A comprehensive fitting to the experimental data approves the acceptability of our stochastic fitting model, originally proposed by Tachiya in his seminal papers . Mechanism of bimolecular PET using QD is different from organic dye mainly in two ways . First, in QD static quenching (through QD‐quencher complex formation) is more probable than dynamic quenching, because the surface passivating layer of QD can easily trap the quencher molecules.…”

“…[35,36] Mechanism of bimolecular PET using QD is different from organic dye mainly in two ways. [37][38][39] First, in QD static quenching (through QD-quencher complex formation) is more probablet han dynamic quenching, because the surface passivating layer of QD can easily trap the quenchermolecules. Second, passivating layer of QD shields the approacho ft he quencher molecules to av ery close to the QD core, which causes an emissive complex formation where efficient PET is retarded.…”

Tuning Hole and Electron Transfer from Photoexcited CdSe Quantum Dots to Phenol Derivatives: Effect of Electron‐Donating and ‐Withdrawing Moieties

“…[44,45] In QDs, ah igh fraction of atoms reside on the surface ( % 56 %a toms for 3nmQ Ds), which interacts with the surroundings. [51] Localization of charge carriers (either electrons or holes) to the surrounding molecules is the main cause of such behavior. [20,49,50] Changes in photoluminescence (PL) quantumy ield and excited-state lifetimei nt he presence of surface molecules also indicate such interactions.…”

“…[20,49,50] Changes in photoluminescence (PL) quantumy ield and excited-state lifetimei nt he presence of surface molecules also indicate such interactions. [51] Localization of charge carriers (either electrons or holes) to the surrounding molecules is the main cause of such behavior. [24][25][26][27][28][29][30] Charge localization can be controlledb ya dding different organic ligands that serve as electron acceptors (Cd 2 + site for CdSe QDs)o rd onors (Se 2À ).…”