Lanthanide-doped nanoparticles are widely investigated for their optical properties. However, the sensitivity of the lanthanide ions’ luminescence to the local symmetry, useful when investigating structural environments, becomes a drawback for optimized properties in the case of poorly controlled crystallinity. In this paper, we focus on β -NaYF4 nanorods in order to provide a detailed description of their chemical composition and microstructure. The combination of detailed XRD analysis and TEM observations show that strong variation may be observed from particles from a same batch of synthesis, but also when considering small variations of synthesis conditions. Moreover, also the nanorods observed by SEM exhibit a very nice faceted shape, they are far from being monocrystalline and present significant local deviation of crystalline symmetry and orientation. All these structural considerations, sensitively probed by polarized emission analysis, are crucial to analyze for the development of optimal systems toward the targeted applications.

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 vanadate...

Trapping of NaYF4:Er/Yb/Gd nanorods using an original optical fiber-tip tweezers is reported. Depending on their length, nanorods are reproducibly trapped in single or dual fiber tip configurations. Short rods of 600 nm length are trapped with two fiber tips facing each other. In contrary, long rods (1.9 μm) can be stably trapped at the apex of one single fiber tip and at a second stable trapping position 5 μm away from the tip. The up-conversion emission of trapped long nanorods is studied as a function of the position on the nanorod and in three orthogonal directions. The experimental results are discussed using numerical simulations based on exact Maxwell Stress Tensor approach.

NaYF4:(Er,Yb,Gd) nanorods of different size were trapped using our original optical tweezers consisting of two fiber tips facing each other. Trapping properties were found to depended drastically on the actual particle size. Small rods were efficiently trapped whereas long rods were strongly attracted by the fiber tips and their stable trapping position was situated at the apex of one single fiber tip. In the case of the long particles the trapped particle modified the fiber tip emission properties and trapping of a second nanorod at distances of some microns from the first one is observed. These experimental results will be explained by numerical simulations using the exact Maxwell Stress Tensor approach.

We are applying our recently developed optical fiber tip nano-tweezers for trapping of luminescent NaYF4:(Er, Yb, Gd) nanorods. The rods were prepared by a solvothermal route based on the reaction between metal and fluoride salts in a mixture of ethanol, water and oleic acid. By controlling the Gadolinium amount it was possible to elaboration rods with very different aspect ratios in the order of 6 to 24, for rod lengths of 640, 940, and 1900 nm.

We report stable and reproducible trapping of luminescent dielectric YAG:Ce3+ nanoparticles with sizes down to 60 nm using far-field dual fiber tip optical tweezers. The particles are synthesized by a specific glycothermal route followed by an original protected annealing step, resulting in significantly enhanced photostability. The tweezers properties are analyzed by studying the trapped particles residual Brownian motion using video or reflected signal records. The trapping potential is harmonic in the transverse direction to the fiber axis, but reveals interference fringes in the axial direction. Large trapping stiffness of 35 and 2 pN mu m(-1) W-1 is measured for a fiber tip-to-tip distance of 3 mu m and 300 nm and 60 nm particles, respectively. The forces acting on the nanoparticles are discussed within the dipolar approximation (gradient and scattering force contributions) or exact calculations using the Maxwell Stress Tensor formalism. Prospects for trapping even smaller particles are discussed.

The unique optical properties of fluorophores nanoparticles doped with rare earth elements have attracted a lot of attention in the scientific community due to their potential application from biological imaging to quantum information. In this work, we compare the photoluminescence of nanoparticles measured by two different means: traditional objective based microscopy and fiber based optical tweezers. Our doped NaYF4 nanocrystals are prepared through solvothermal synthesis. Ytterbium and erbium codoping provides nanoparticles with luminescence properties. Under IR laser excitation, the nanoparticles present strong and photostable upconversion signals in the visible range. In addition, by changing the gadolinium content of the host matrix, we obtain nanorods with a controlled aspect ratio up to 20 and a well defined crystalline structure. The high anisotropy of the nanoparticles results in a strong polarisation of the photoluminescence. To investigate this property, we observed our nanoparticles using a confocal microscope and studied the dependency of the polarisation with the length of the particles. To complete our characterization, we used optical tweezers to trap nanoparticles in water. We first show the possibility to trap these nanoparticles with an original optical tweezers based on two chemically etched fibers. Due to the optical forces applied by the laser beam coupled into the fibers, the nanorods align themselves between the two fibers along their long axis. Afterwards, the fibers are not only used to trap the particles but also to collect the luminescence emitted only by the trapped nanoparticles. By this mean, we can analyse the emitted light with a spatial resolution. This result will be compare to previous observation done on the same particles with our confocal microscope. Moreover, an orthogonal third fiber was implemented in the set up. This fiber can move along the particle and collect the light emitted at different point. We present the link between the photoluminescence properties and the emission point by moving this last fiber. In addition, our optical tweezers are associated to a traditional objective-based optical microscope. We compared the photoluminescence emitted by particles in a homogeneous medium (water) or at an interface when drop casted on a coverslip.

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.

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.

Arrays of liquid crystal defects—linear smectic dislocations—are used to trap semiconductor CdSe/CdS dot‐in‐rods which behave as single‐photon emitters. Measurements of the emission diagram are combined together with measurements of the emitted polarization of the single emitters. It is shown that the dot‐in‐rods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. It is demonstrated that the electric dipoles associated with the dot‐in‐rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and perpendicular to the substrate, most likely due to dipole/dipole interactions between the dipoles of the liquid crystal molecules and those of the dot‐in‐rods. Using smectic dislocations, nanorods can consequently be oriented 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 dot‐in‐rods' dipoles. These results open the way for the fine control of nanoparticle anisotropic optical properties, in particular, fine control of single‐photon emission polarization.

Some cellular mechanisms such as migration and invasion, are determined and regulated by cell mechanical properties, especially during embryonic development or tumorigenesis. In these cases, cells attitude to undergo deformation and to displace their whole body is a crucial point for survival and metastasis formation. Extracellular environment three-dimensionality is a key feature influencing cell mechanics, and micro- and nano-fabricated structures represent a promising tool to study cell behavior. Here we engineer 3D- cage-like microstructures realized by two-photon polymerization to analyze cell migration through pores significantly smaller than the cell nucleus. We found that cells spontaneously interact with the cages by applying force at the cell-cage contact points while rearranging their cytoskeleton. The ability to traverse pores of different area depends on the invasiveness of the cell lines, allowing to discriminate between cells with different invasive potential.

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.

We experimentally demonstrate that two-photon pumping of "dark" excitons in quantum wells embedded in semiconductor microcavities can result in exciton-polariton injection and photon lasing. In the case of a semiconductor micropillar pumped at half of the exciton frequency, we observe a clear threshold behavior, characteristic of the vertical cavity surface emitting laser transition. These results are interpreted in terms of stimulated emission of terahertz photons, which allows for conversion of "dark" excitons into exciton-polaritons.

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.

In this work we propose rod-shaped core/shell CdSe/CdS colloidal nanocrystals as efficient non-classical light sources. These nanoemitters show peculiar features such as pronounced photoluminescence stability and high single-photon emission efficiency at room-temperature, making us envision their possible employment as single-photon sources for quantum communications protocols.

CdSe/CdS dot-in-rod (DR) nanocrystals, i.e. semiconductor nanoparticles consisting of a CdSe spherical core surrounded by a rod-shaped CdS shell, recently emerged as efficient sources of non-classical light for quantum cryptography applications. This paper discusses the influence of shell size on DRs quantum emission properties, showing that shell elongation has detrimental effects on DRs single photon emission effectiveness.

Blinking effect and multi-excitonic emission can be independently addressed by tuning both core and shell dimension. By confocal techniques measurement, we show dot-in-rods as blinking-free sources of single photon on demand at room temperature.

We report on the development of efficient and low cost single photon sources for quantum communications. The work discusses the suitability of colloidal nanocrystals as sources of quantum light as well as it draws out possible solutions to overtake the drawbacks of these emitters, such as blinking and polarization.

We present a technique based on a two-photon absorption process. We coherently inject polaritons in planar or pillar microcavities, being in resonance and with a well defined in plane wavevector (k) and show polariton laser.