A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime, and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantized vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies.

We present a method that allows determining the band-edge exciton fine structure of CdSe/CdS dot-in-rods samples based on single particle polarization measurements at room temperature. We model the measured emission polarization of such single particles considering the fine structure properties, the dielectric effect induced by the anisotropic shell, and the measurement configuration. We use this method to characterize the band-edge exciton fine structure splitting of various samples of dot-in-rods. We show that, when the diameter of the CdSe core increases, a transition from a spherical like band-edge exciton symmetry to a rod-like band edge exciton symmetry occurs. This explains the often reported large emission polarization of such particles compared to spherical CdSe/CdS emitters.

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Carbon Dots (CDs) are a new promising type of small (5 nm), biocompatible and multicolor luminescent nanoparticle. Here, we demonstrate super-resolution imaging of CDs at the nanoscale through STimulated Emission Depletion (STED) microscopy. In addition, we report the application of STED for detection of CD localization in both fixed and living cells, achieving a spatial resolution down to 30 nm, far below the diffraction limit, showing great promise for high resolution visualization of cellular dynamics.

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.

Cancer cell motility is one of the major events involved in metastatic process. Tumor cells that disseminate from a primary tumor can migrate into the vascular system and, being carried by the bloodstream, transmigrate across the endothelium, giving rise to a new tumor site. However, during the invasive process, tumor cells must pass through the extracellular matrix, whose structural and mechanical properties define the parameters of the migration process. Here, we propose 3D-complex cage-like microstructures, realized by two-photon (TP) direct laser writing (DLW), to analyze cell migration through pores significantly smaller than the cell nucleus. We found that the ability to traverse differently sized pores depends on the metastatic potential and on the invasiveness of the cell lines, allowing to establish a pore-area threshold value able to discriminate between non-tumorigenic and tumorigenic human breast cells.

We use arrays of liquid crystal defects, linear smectic dislocations, to trap semi-conductor CdSe/CdS dot-in-rods which behave as single photon emitters. We combine measurements of the emission diagram together with measurements of the emitted polarization of the single emitters. We show that the dot-inrods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. We demonstrate that the electric dipoles associated with the dotin-rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and being perpendicular to the substrate, most likely due to the dipole/dipole interactions between the dipoles of the liquid crystal molecules and the dot-in-rods ones. Using smectic dislocations, we can consequently orient nanorods along a unique direction for a given substrate, independently of the ligands' nature, without any induced aggregation, leading as well to a fixed azimuthal orientation for the associated dot-in-rods' dipoles. These results open the way for a fine control of nanoparticle anisotropic optical properties, in particular a fine control of single photon emission polarization.Control of single photon emitters is a major objective in the field of nanophotonics.[1] The synthesis of colloidal semiconductor inorganic nanocrystals having specific light-emission properties has been providing important advances in this field. In particular, recent developments in synthesis methodologies, fully compatible with standard nanofabrication technologies have enabled a superior 3 control on nanocrystals composition and morphology.Rod-shaped nanocrystals showing pronounced polarization, behaving as emitting linear dipoles, have been obtained. [2][3][4] The encapsulation of a spherical core into a rod-like shell [5] resulted in non-blinking inorganic single photon emitters, [6] hereafter referred to as dot-in-rods (DRs). Moreover it has been recently shown that, by increasing the thickness of the shell, it is possible to greatly suppress photoluminescence blinking and to improve DRs overall photo-stability, while keeping a low probability of multi-photon emission. [7] Such features are of primary importance when nanocrystalsare used in applications demanding a control of photons'polarization, such as coupling with complex photonic cavities [8][9] or quantum cryptography.[10] The control of the polarization of the emitted light also requires the capacity to control the particle orientation. Howevertechnologies aimed at guiding nanocrystal orientation at the single particle level are still poorly discussed in literature.Alignednanoparticleshave been obtained through mechanical rubbing, [11] short-range interactions [12][13] or patterned substrates. [14] Liquid crystal-like structures, composed of alarge number of elongated nanocrystalsassembled in multi-layers have also been evidenced on both solid substrates [15][16][17][18] and water films. [18][19][20] Orientation and positional ordering of CdS and CdSe...

Thulium/ytterbium-doped yttrium vanadate particles provide a ratiometric thermal response as both colloids and powders via downshift or upconversion emissions. Here, we synthesized yttrium vanadates by controlled colloidal conversion of hydroxycarbonate precursors. A protected annealing process yielded single crystalline and readily dispersible particles that were manipulated individually by optical tweezers in water. Because individual particles displayed detectable emissions, this system has potential applications as a single-particle luminescent temperature sensor. Excitation on Yb3+ sensitizers (λexc = 980 nm) or at vanadate groups (λexc = 300 nm) resulted in Tm3+ emissions that effectively correlated with the temperature of the sample from 288 to 473 K with high relative thermal sensitivity (0.8–2.2% K–1), one of the highest reported for vanadate nanocrystals so far. Different pairs of Tm3+ transitions afford a ratiometric thermal response, which fitted common sensing requirements such as large [3F2,3 → 3H6 (λ = 700 nm)/1G4 → 3H6 (λ = 475 nm)] or small [3F2,3 → 3H6 (λ = 700 nm)/1G4 → 3F4 (λ = 650 nm)] spectral gaps and emission wavelengths at the first near-infrared biological window [3F2,3 → 3H6 (λ = 700 nm)/3H4 → 3H6 (λ = 800 nm)]. Our findings open new perspectives for the use of luminescent nanothermometers with controllable spatial localization, which is a remarkably interesting prospect to investigate microscopically localized events related to changes in temperature.