Directed Energy Transfer in Films of CdSe Quantum Dots: Beyond the Point Dipole Approximation

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• 作者：Kaibo Zheng ; Karel 沤铆dek ; Mohamed Abdellah ; Nan Zhu ; Pavel Ch谩bera ; Nils Lenngren ; Qijin Chi ; T玫nu Pullerits
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：April 30, 2014
• 年：2014
• 卷：136
• 期：17
• 页码：6259-6268
• 全文大小：589K
• 年卷期：v.136,no.17(April 30, 2014)
• ISSN：1520-5126

文摘

Understanding of F枚rster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size of QDs, so that the simple point鈥揹ipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using ultrafast transient absorption spectroscopy and theoretical modeling. Pairwise interdot transfer time was determined in the range of 1.5 to 2 ns by spectral analyses which enable separation of the FRET contribution from intrinsic exciton decay. A rational model is suggested by taking into account the distribution of the electronic transition densities in the dots and using the film morphology revealed by AFM images. The FRET dynamics predicted by the model are in good quantitative agreement with experimental observations without adjustable parameters. Finally, we use our theoretical model to calculate dynamics of directed energy transfer in ordered multilayer QD films, which we also observe experimentally. The Monte Carlo simulations reveal that three ideal QD monolayers can provide exciton funneling efficiency above 80% from the most distant layer. Thereby, utilization of directed energy transfer can significantly improve light harvesting efficiency of QD devices.