The coupling between thick-shell CdSe/CdS colloidal nanocrystals with the hot spots of a semicontinuous gold film is characterized by measuring simultaneously the photoluminescence decay rate and the linear polarization ratio. The absence of correlations between the two quantities is demonstrated. In contrast with the results obtained with continuous gold films, polarization ratios higher than 80% are achieved for the smallest nanocrystals. This ratio decreases quickly when the nanocrystals size is increased.
Efficient coupling of nanoemitters to photonic or plasmonic structures requires the control of the orientation of the emitting dipoles. Nevertheless controlling the dipole orientation remains an experimental challenge. Many experiments rely on the realization of numerous samples, in order to be able to statistically get a well aligned dipole to realize an efficient coupling to a nanostructure. In order to avoid these statistical trials, the knowledge of the nature of the emitter and its orientation is crucial for a deterministical approach. We developed a method , relying on the combination of polarimetric measurement and emission diagram which gives fine information both on the emitting dipolar transition involved and on the dipolar orientation
We analyse by this method square and rectangle single colloidal CdSe/CdS nanoplatetelets. We demonstrate that their emission can be described by just by two orthogonal dipoles lying in the plane of the platelets. More surprisingly the emission of the square nanoplatelets is not polarised whereas the rectangle one is. We demonstrate that this polarized emission is due to the rectangular shape anisotropy by a dielectric effect.
 C. Lethiec, et al, Three-dimensional orientation measurement of a single fluorescent nanoemitter by polarization analysis, Phys. Rev. X 4, 021037 (2014),
 C. Lethiec et al, Polarimetry-based analysis of dipolar transitions of single colloidal CdSe/CdS dot-inrods, New Journal of Physics 16, 093014 (2014)
 S. Ithurria et al, colloidal nanoplatelets with 2 dimensional electronic structure, Nature Materials 10, 936 (2011)
Plasmonic nano-antennas provide broadband spontaneous emission control by confining light on highly sub-wavelength volumes. We realize a plasmonic patch antenna by positioning a emitter within a ultrathin slab of dielectric limited by an optically thick gold layer and a thin gold patch. A single CdSe/CdS colloidal quantum dot is deterministically located just in the center of the antenna by an original in situ optical lithography protocol . Depending on the dimension of the patch antenna and the emitter orientation, different Purcell factors could be achieved leading to different optical properties. For moderate Purcell factors, patch nanoantennas are plasmonic directive single photon sources. For higher Purcell factors, the spontaneous emission acceleration makes the multiexciton radiative recombination more efficient than Auger non radiative recombination. Emission of photons due to multiexcitons recombination could be observe at very short time scale. Such antennas can be very efficiently excited. Such antenna appear to be extremely bright as their luminescence exceed by more than one order of magnitude the one of single nanocrystals.
 Dousse, A. et al. Controlled light-matter coupling for a single quantum dot embedded in a pillar microcavity using far-field optical lithography. Phys. Rev. Lett. 101, 267404 (2008).
 C. Belacel, B. Habert, F. Bigourdan, F. Marquier, J-P. Hugonin, S. Michaelis de Vasconcellos, X. Lafosse, L. Coolen, C. Schwob, C. Javaux, B. Dubertret, J-J. Greffet, P. Senellart, A. Maître, Controlling spontaneous emission with plasmonic optical patch antennas, Nanoletters 13 1516 (2013)
Efficient coupling of nanoemitters to photonic or plasmonic structures requires the control of the orientation of the
emitting dipoles related to the emitter. Nevertheless the knowledge of the dipole orientation remains an experimental
challenge. Many experiments rely on the realization of large sets of samples, in order to be able to get one nanostructure
coupled to a well aligned dipole. In order to avoid these statistical trials, the knowledge of the nature of the emitter
(single or double dipole) and its orientation are both crucial for a deterministic approach. Based on the theoretical
development of the point-dipole emission, we propose in this paper to determine the nature and the polarization of two
types of nanoemitters (spherical nanocrystals and dot-in-rod) by the analysis of their emission polarization [1,2]. The
nanoemitters we considered in this study are colloidal semiconductor (CdSe/CdS) nanocrystals with different sizes and
aspect ratio, allowing us to establish a relationship between the geometry of a nanoemitter and the nature and orientation
of its associated radiating dipole.
Colloidal fluorescent semiconductor nanocrystals, named “quantum dots”, possess unique features, such as a tunable peak wavelength (according to their composition and their size) or a large absorption cross-section, that make them very attractive for biomedical imaging. Nevertheless, typical syntheses provide nanoparticles capped with hydrophobic ligands. To be used in long-term bioexperiments, they have thus to be modified to exhibit essentially a high colloidal stability in aqueous conditions, but also a low non-specific adsorption, a small size and functionalization moities. As all of these properties are controlled by the layer of coating ligands, we designed a bidentate monozwitterionic ligand, to first address the need of small-sized and antibiofouling hydrophilic probes. But the corresponding quantum dots revealed to be unstable in highly diluted conditions and difficult to functionalize. To further increase the affinity between the nanoparticles and their surrounding ligands, we synthesized a multidentate polyzwitterionic ligand, issued from the copolymerization of a bidentate monomer and a monozwitterionic one. The nanocrystals passivated by this polymeric ligand showed an exceptional colloidal stability, regardless of the medium conditions (pH, salinity, dilution, and biological environment), and we demonstrated the affinity of the polymer exceeded by three orders of magnitude that of the bidentate ligand. The synthesis of the multidentate polyzwitterionic ligand proved also to be easily tunable and allowed the facile introduction of reacting moieties. Further functionalization of the corresponding quantum dots with biomolecules led to successful specific targeting, which could be confirmed, as an example, through FRET experiments.
We developed a high-resolution microscope based on three-dimensional structured illumination generated with two
spatial light modulators. This setup enables both lateral resolution improvement by a factor two and axial localization of
point like objects with nanometric precision.
Quantum dots are nanometre-sized semiconductor particles exhibiting unique size-dependent electronic
properties. In order to passivate the nanocrystals surface and to protect them from oxidation, we grow a shell
composed of a second semiconductor with a larger bandgap on the core (for example a core / shell CdS / ZnS).
However, the lattice mismatch between the two materials (typically 7% between ZnS and CdS) induces
mechanical stress which can lead to dislocations. To better understand these mechanisms, it is important to be
able to measure the pressure induced on the semiconductor core. We used a nanocrystal doped with manganese
ions Mn2+, which provide a phosphorescence signal depending on the local pressure. A few dopant atoms per
nanoparticle were placed at controlled radial positions in a ZnS shell formed layer by layer. The experimental
pressure measurements are in very good agreement with a simple spherically symmetric elastic continuum
model. Using manganese as a pressure gauge could be used to better understand some structural phenomena
observed in these nanocrystals, such as crystalline phases transition, or shell cracking.
Fluorescence spectroscopy studies have shown that, 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. Statistical analysis of these intensity fluctuations has demonstrated that the dark
states duration exhibits a universal heavy-tailed power law distribution in organic as well as inorganic
fluorophores. However, the precise reasons underlying the blinking of single fluorophores are still matter of
debate and whether it can be suppressed is not clear. Here we have synthesized CdSe/CdS core/shell quantum
dots (QDs) with thick crystalline shells, which do not blink at low frame rate and established a direct correlation
between shell thickness and blinking occurrences. Single fluorophore blinking and blinking statistics are thus not
as universal as thought so far. We anticipate our results to help better understand the physicochemistry of single
fluorophore emission and rationalize the design of other fluorophores that do not blink. The materials presented
here should readily find interesting applications in biology for single molecule tracking and in photonics as
robust and continuous photon emitter.
Semiconductor quantum dot nanocrystals (QDs) have unique optical properties such as size tunable photoluminescence (PL) wavelength and a chemically functionalized sufrace. Our CdSe/ZnS quantum dot nanocrystals have been made water-soluble by encapsulation in a micelle of positively charged amphiphilic copolymers. Layer-by-layer deposition of these QDs was done on sub-micrometer silica beads as well as magnetic and polymeric micro-sized beads. The negative surface charge of these various beads allowed successive stacking of cationic polyethylnimine, anionic polyacrylic acid sodium salt and the cationic encapsulated QDs. Multiple QD layers can be added by repeating the stacking process. The PL spectral of green QDs is moduoated by whispering galley mode resonances when the QDs arecoating a singe 3 μm bead. Depending on the quality factor of this microsphere, it can also be possible to detect perturbations caused by sufficient adsorption of biomolecules or even living microorganisms on a bead's surface by observing spectral shifts of the resonances. If different colorsof QDs are used to coat smaller beads where the modes are not spectrally resolved, an optical coating system can be devised base on the relative emission intensity for each color. The uniformity of a bead ensemble coded with 2 QD colors has been invesetigated, revealing a ~20% relataive standard deviation for various intensity levels. Better control of photobleaching through QD passivation reduced this number to ~8%, which would allow us to differentiate up to 2.6x1010 optical codes on our setup. Labelling large amount of molecules in solution, e.g. DNA sequences, then becomes possible with an appropriate biofunctionalization of bead surfaces.