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An Ultrafast Transient Absorption Study of Charge Separation and Recombination Dynamics in CdSe QDs and Methyl Viologen: Dependence on Surface Stoichiometry
Author(s) -
Sekhar M. Chandra,
Paul Sneha,
De Apurba,
Samanta Anunay
Publication year - 2018
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201800313
Subject(s) - ultrafast laser spectroscopy , electron transfer , stoichiometry , viologen , quantum dot , absorption (acoustics) , quantum yield , excited state , chemistry , analytical chemistry (journal) , photochemistry , yield (engineering) , materials science , chemical physics , atomic physics , fluorescence , spectroscopy , nanotechnology , optics , physics , chromatography , metallurgy , composite material , quantum mechanics
The dependence of the dynamics of charge separation and recombination between methyl viologen (MV +2 ) and photo‐excited CdSe quantum dots (QDs) on the surface stoichiometry of the latter is studied for QDs with different Cd:Se mole ratios employing ultrafast time‐resolved absorption and emission measurements. The electron transfer rates between photoexcited CdSe QDs and MV +2 are measured directly by monitoring the ultrafast rise and decay of the transient absorption signal due to methyl viologen monocationic radical (MV +• ). The results show that both forward and back electron transfer rates (5±1 x 10 12 s −1 and 1.3±0.3 x 10 10 s −1 , respectively) are independent of the stoichiometry of the QDs. Interestingly, the efficiency of the electron transfer process, estimated from the yield of MV +• , shows significant dependence on the nature of the QDs, with maximum yield (Φ rs =0.52±0.01) observed in the case of Cd‐rich QDs. These findings are explained considering the energetics and surface trap states of these systems.