Correlated blinking of fluorescent emitters mediated by single plasmons

We observe time-correlated emission between a single CdSe/CdS/ZnS quantum dot exhibiting single-photon statistics and a fluorescent nanobead located micrometers apart. This is accomplished by coupling both emitters to a silver nanowire. Single plasmons are created on the latter from the quantum dot, and transfer energy to excite in turn the fluorescent nanobead. We demonstrate that the molecules inside the bead show the same blinking behavior as the quantum dot.

Figure 1

(a) Optical setup used for imaging, spectroscopy, and time-resolved measurements of a QD (donor) and a fluorescent bead (acceptor) coupled to a silver nanowire. (b) Normalized emission spectra of the QD (in blue) and the acceptor bead (in red). The absorption spectrum of the bead is the red dashed curve. Transmittance of the dichroic mirror and of the long-pass filter are represented in light gray and gray, respectively. (c) Top: Artist view of the experiment. Bottom: Electron multiplying CCD (EM-CCD) taken during the experiment, while the laser is focused on the QD. Bright spots are detected at the position of both emitters as well as both ends of the nanowire.

Figure 2

(a) Time dependence of the fluorescence counts of the QD, time bin equal to 1 ms (in blue). The drift of the experiment is represented by the dashed line. (b) Distribution of detected events, showing a clear distinction between the bright and the dark state of the QD. (c) Fluorescence decay histograms of a single QD on glass (light blue) and on the nanowire (dark blue). (d) Fluorescence decay histogram for the acceptor on glass and on wire, when excited via a plasmon.

Figure 3

Measured decay histogram of the acceptor together with the model function (in orange). Error bars correspond to $\pm 2$ standard deviations (95% confidence level). Inset: Fit functions of the decay histograms of the QD (blue curve) and the acceptor (A, red curve) excited independently and their convolution (ET, orange curve).

Figure 4

(a) Correlation coefficient of the QD fluorescence (SPAD 1) and the acceptor fluorescence (SPAD 2) as defined in Eq. (1). (b) Correlation coefficient for an experiment in which we measure the QD fluorescence (SPAD 1) and the light scattered by the nanowire end (SPAD 2).

Figure 5

(a) Single CdSe/CdS/ZnS nanocrystal on glass. Repetition rate: 5 MHz. Measured fluorescent counts of the bright state: 20 c/ms. (b) Single CdSe/CdS/ZnS nanocrystal on silver nanowire. Repetition rate: 40 MHz. Measured fluorescent counts of the bright state: 300 c/ms.

Figure 6

(a) Scheme of the experiment. (b) Measured decay histogram in three different situations: bead not coupled to a nanowire (blue), bead coupled to a nanowire and excited directly by the laser (green), same bead excited by a surface plasmon launched by focusing a laser on the extremity of the nanowire (red). (c) Distribution of decay rates for these three situations.

Figure 7

(a) Experimental data binned at 64 ps (in orange). The black curve is a fit of the data by the IRF. (b) Corrected data binned at 700 ps.