Strong Purcell effect observed in single thick-shell CdSe/CdS nanocrystals coupled to localized surface plasmons

High-quality-factor dielectric cavities designed to a nanoscale accuracy are mostly used to increase the spontaneous emission rate of a single emitter. Here we show that the coupling, at room temperature, between thick-shell CdSe/CdS nanocrystals and random metallic films offers a very promising alternative approach. Optical modes confined at the nanoscale induce strong Purcell factors reaching values as high as 60. Moreover, the quantum emission properties can be tailored: strong antibunching or radiative biexcitonic cascades can be obtained with high photon collection efficiency and extremely reduced blinking.

Figure 1

Schematic representation of the bright (a) and gray (b) states.

Figure 2

(a) Topography of the gold film realized with an AFM. (b) Absorbance (A), transmittance (T), and reflectance (R) of the random gold film. The laser diode wavelength (Laser) is represented as well as the NCs photoluminescence (NCs).

Figure 3

Coincidence counts for a typical NC deposited on a glass coverslip.

Figure 4

(a) Fluorescence intensity of a single CdSe/CdS NC on a glass coverslip ($t_b=$ 10 ms). The background level is 0.3 count per time bin and can be neglected. (b) Histogram of the intensity corresponding to (a). (c) PL decay of the bright state (peak B). The red line is a monoexponential fit (with an offset, lifetime of 75 ns). (d) PL decay of the low emitting periods (bump A). The red line is a biexponential fit (lifetimes of 69 and 12 ns).

Figure 5

(a) Sketch of NCs deposited on the semicontinuous gold film. The topography of the gold film has been realized with an AFM. NCs are represented to scale. (b) PL decay of three NCs illustrating the range of decay rates. The PL decay of NC${}_{\mathrm{FAST}}$ is very fast. NC${}_{\mathrm{INT}}$ corresponds to an intermediate case. For the NC labeled NC${}_{\mathrm{SLOW}}$, the decay is relatively slow.

Figure 6

Coincidence counts for NC${}_{\mathrm{FAST}}$ (a) and NC${}_{\mathrm{SLOW}}$ (b).

Figure 7

(a) Fluorescence intensity of NC${}_{\mathrm{FAST}}$ ($t_b=$ 10 ms). (b) Histogram of the intensity corresponding to (a). The dots are the experimental results. The red line is a Poissonian distribution fit (mean value of 47). (c) PL decay of NC${}_{\mathrm{FAST}}$. The red line is a biexponential fit (lifetimes of 0.49 and 1.28 ns). (d) Fluorescence intensity of NC${}_{\mathrm{SLOW}}$ ($t_b=$ 2.5 ms). (e) Histogram of the intensity corresponding to panel (d). The dots are the experimental results. The red line is a Poissonian distribution fit (mean value of 37). (f) PL decay of NC${}_{\mathrm{SLOW}}$. The red line is a biexponential fit (lifetimes of 0.9 and 5.49 ns).