Jean-Pierre Hermier

Towards non-blinking colloidal quantum|[nbsp]|dots

At a single-molecule level, fluorophore emission intensity fluctuates between bright and dark states. These fluctuations, known as blinking, limit the use of fluorophores in single-molecule experiments. The dark-state duration shows a universal heavy-tailed power-law distribution characterized by the occurrence of long non-emissive periods. Here we have synthesized novel CdSe-CdS core-shell quantum dots with thick crystalline shells, 68% of which do not blink when observed individually at 33 Hz for 5 min. We have established a direct correlation between shell thickness and blinking occurrences. Importantly, the statistics of dark periods that appear at high acquisition rates (1 kHz) are not heavy tailed, in striking contrast with previous observations. Blinking statistics are thus not as universal as thought so far. We anticipate that our results will help to better understand the physico-chemistry of single-fluorophore emission and rationalize the design of other fluorophores that do not blink.

Statistical aging and nonergodicity in the fluorescence of single nanocrystals.

The relation between single particle and ensemble measurements is addressed for semiconductor CdSe nanocrystals. We record their fluorescence at the single molecule level and analyze their emission intermittency, which is governed by unusual random processes known as Lévy statistics. We report the observation of statistical aging and ergodicity breaking, both related to the occurrence of Lévy statistics. Our results show that the behavior of ensemble quantities, such as the total fluorescence of an ensemble of nanocrystals, can differ from the time-averaged individual quantities, and must be interpreted with care.

Measurement of the radiative and nonradiative decay rates of single CdSe nanocrystals through a controlled modification of their spontaneous emission.

We present a simple method to measure the radiative and nonradiative recombination rates of individual fluorescent emitters at room temperature. By placing a single molecule successively close and far from a dielectric interface and simultaneously measuring its photoluminescence decay and its orientation, both the radiative and nonradiative recombination rates can be determined. For CdSe nanocrystals, our results demonstrate that the fluorescence quantum efficiency, determined at the single-molecule level, is 98% in average, far above the value expected from conventional ensemble experiments. The bidimensional nature of the transition dipole is also directly evidenced from a single-particle measurement.

Bunching and antibunching in the fluorescence of semiconductor nanocrystals

The fluorescence of single-colloidal CdSe quantum dots is investigated at room temperature by means of the autocorrelation function over a time scale of almost 12 orders of magnitude. Over a short time scale, the autocorrelation function shows complete antibunching, indicating single-photon emission and atomiclike behavior. Over longer time scales (up to tens of seconds), we measure a bunching effect that is due to fluorescence intermittency and that cannot be described by fluctuations between two states with constant rates. The autocorrelation function also exhibits nonstationary behavior related to power-law distributions of On and Off times.

Highly efficient triggered emission of single photons by colloidal CdSe∕ZnS nanocrystals

We demonstrate the realization of a highly efficient triggered source of single photons emitted by colloidal CdSe∕ZnS nanocrystals at room temperature. Under pulsed excitation, the fluorescence of single nanocrystals excited close to saturation exhibits a perfect antibunching and the probability to detect a single emitted photon per excitation pulse reaches 3%, comparable to the best values reported for other emitters. Without any correction, the probability of simultaneously emitting two photons is 25 times lower than for a faint pulsed laser. Combined with recent reports on the reduction of fluorescence intermittency, these results indicate that CdSe∕ZnS nanocrystals are promising single-photon sources.

Colloidal CdSe/ZnS quantum dots as single-photon sources

The fluorescence of colloidal CdSe/ZnS nanocrystals at room temperature exhibits a perfect antibunching under continuous or pulsed excitation. In this paper, we discuss the consequences of fluorescence properties of CdSe nanocrystals on the generation of single photons. In particular, we examine the role of Auger processes in the inhibition of multiexcitonic emission. We also discuss the relationship between Auger processes and the fluorescence intermittency of CdSe quantum dots. Altogether, features discussed here indicate that CdSe/ZnS nanocrystals are promising single-photon sources.

Room temperature-dipolelike single photon source with a colloidal dot-in-rod

We propose colloidal CdSe/CdS dots in rods as nonclassical sources for quantum information technology. Such nanoemitters show specific properties such as strongly polarized emission of on-demand single photons at room temperature, dipolelike behavior and mono-exponential recombination rates, making us envision their suitability as sources of single photons with well defined quantum states in quantum cryptography based devices.

Non-blinking single-photon generation with anisotropic colloidal nanocrystals: towards room-temperature, efficient, colloidal quantum sources.

Blinking and single-photon emission can be tailored in CdSe/CdS core/shell colloidal dot-in-rods. By increasing the shell thickness it is possible to obtain almost non-blinking nanocrystals, while the shell length can be used to control single-photon emission probability.

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.

Non‐Blinking Semiconductor Colloidal Quantum Dots for Biology, Optoelectronics and Quantum Optics

Twinkle, twinkle: The blinking of semiconductor colloidal nanocrystals is the main inconvenience of these bright nanoemitters. There are various approaches for obtaining non-blinking nanocrystals, one of which is to grow a thick coat of CdS on the CdSe core (see picture). Applications of this method in the fields of optoelectronic devices, biologic labelling and quantum information processing are discussed.The blinking of semiconductor colloidal nanocrystals is the main inconvenience of these bright nanoemitters. For some years, research on this phenomenon has demonstrated the possibility to progress beyond this problem by suppressing this fluorescence intermittency in various ways. After a brief overview on the microscopic mechanism of blinking, we review the various approaches used to obtain non-blinking nanocrystals and discuss the commitment of this crucial improvement to applications in the fields of optoelectronic devices, biologic labelling and quantum information processing.