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Competition between Energy and Electron Transfer from CdSe QDs to Adsorbed Rhodamine B

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journal contribution
posted on 21.01.2010, 00:00 by Abdelaziz Boulesbaa, Zhuangqun Huang, David Wu, Tianquan Lian
Understanding the dynamics of exciton quenching in quantum dots (QDs) is essential to their potential applications, such as solar cells and biological imaging. In this work, the competition between electron and energy transfer from excited CdSe QDs to adsorbed rhodamine B (RhB) molecules was examined by time-resolved fluorescence decay, steady-state emission, and transient absorption measurements. The major pathway (84%) for exciton quenching in this system is through electron transfer to RhB, whereas ∼16% of the excitons decay by energy transfer. In a sample with ∼2−3 RhB per QD, exciton quenching occurs with an average time constant of 54 ps, and the charge-separated state has an average lifetime of 1 μs. The charge separation rate depends on the number of adsorbates attached to the QD, and the dependence can be well-described by a kinetics model that assumes a Poisson distribution of the number of adsorbates on the QDs.