Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots

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Abstract

Photoluminescence blinking—random switching between states of high (ON) and low (OFF) emissivities—is a universal property of molecular emitters found in dyes1, polymers2, biological molecules3 and artificial nanostructures such as nanocrystal quantum dots, carbon nanotubes and nanowires4,5,6. For the past 15 years, colloidal nanocrystals have been used as a model system to study this phenomenon5,6. The occurrence of OFF periods in nanocrystal emission has been commonly attributed to the presence of an additional charge7, which leads to photoluminescence quenching by non-radiative recombination (the Auger mechanism)8. However, this ‘charging’ model was recently challenged in several reports9,10. Here we report time-resolved photoluminescence studies of individual nanocrystal quantum dots performed while electrochemically controlling the degree of their charging, with the goal of clarifying the role of charging in blinking. We find that two distinct types of blinking are possible: conventional (A-type) blinking due to charging and discharging of the nanocrystal core, in which lower photoluminescence intensities correlate with shorter photoluminescence lifetimes; and a second sort (B-type), in which large changes in the emission intensity are not accompanied by significant changes in emission dynamics. We attribute B-type blinking to charge fluctuations in the electron-accepting surface sites. When unoccupied, these sites intercept ‘hot’ electrons before they relax into emitting core states. Both blinking mechanisms can be electrochemically controlled and completely suppressed by application of an appropriate potential.

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Figure 1: Conventional charging model: A-type blinking and flickering.
Figure 2: Experimental set-up and electrochemical charging of an individual nanocrystal.
Figure 3: Correlated photoluminescence intensity and lifetime fluctuations: A-type blinking and flickering.
Figure 4: Photoluminescence intensity fluctuations without lifetime changes: B-type blinking.
Figure 5: Electrochemically controlled switching between distinct statistics for ON and OFF times in the same nanocrystal, accompanying the transition from B-type to A-type blinking.

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Acknowledgements

C.G. and V.I.K. acknowledge support of the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES). Y.G. and A.S. are supported by Los Alamos National Laboratory Directed Research and Development Fund. M.S., J.A.H. and H.H. are supported by NIH-NIGMS grant 1R01GM084702–01. This work was conducted, in part, at the Center for Integrated Nanotechnologies, a DOE/BES user facility.

Author information

C.G., M.S., J.A.H., V.I.K. and H.H. conceived the study. C.G., M.S. and H.H. designed the experiments. C.G. constructed the experimental set-up and performed the measurements under the guidance of M.S., V.I.K. and H.H. Y.G. synthesized and A.S. modified quantum dot materials under the guidance of J.A.H. C.G., V.I.K. and H.H. analysed and interpreted the data, and wrote the manuscript with the assistance of all other co-authors.

Correspondence to Milan Sykora or Victor I. Klimov or Han Htoon.

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This file contains Supplementary Text and Data 1-4, additional references, Supplementary Figures 1-13 with legends and Supplementary Tables 1-2. (PDF 1111 kb)

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Galland, C., Ghosh, Y., Steinbrück, A. et al. Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots. Nature 479, 203–207 (2011) doi:10.1038/nature10569

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