The optical range of localized surface plasmon resonance (LSPR) is extended into the infrared region, thanks to the development of highly doped semiconductor nanocrystals. Particularly, the near-infrared (NIR) range holds a significant interest in managing solar radiation. However, practical applications necessitate the arrangement of particles, which is known to possibly impact their optical properties through LSPR coupling effects. How such coupling modifies the LSPR response in semiconductor hosts remains largely unexplored. In this study, a protocol for producing composite coatings composed of cesium-doped tungsten bronze nanocrystals embedded in a silica matrix is presented. Achieving individual dispersion of nanocrystals is made possible through careful selection of a surface polyglycerol ligand exchange. This allows to tune the interparticle distance by adjusting the nanocrystal volume fraction in the composite. The findings demonstrate that LSPR coupling effects significantly influence the LSPR intensity of nanocrystals in the composite when the nanocrystal-to-nanocrystal distance matches their size. Beyond elucidating the LSPR coupling effect, this study provides insights into the potential use of Cs-HTB nanocrystals for solar control applications. Through the optimization of morphology and film structure, remarkable selectivity is obtained in terms of maintaining good transparency in the visible range while achieving high absorption in the NIR.

Concentrated colloidal suspensions of nanorods often exhibit liquid-crystalline (LC) behavior. The transition to a nematic LC phase, with long-range orientational order of the particles, is usually well captured by Onsager's theory for hard rods, at least qualitatively. The theory shows how the volume fraction at the transition decreases with increasing aspect ratio of the rods. It also explains that the long-range electrostatic repulsive interaction occurring between rods stabilized by their surface charge can significantly increase their effective diameter, resulting in a decrease of the volume fraction at the transition, as compared to sterically stabilized rods. Here, we report on a system of ligand-stabilized LaPO4 nanorods, of aspect ratio around 11, dispersed in apolar medium exhibiting the counter-intuitive observation that the onset of nematic self-assembly occurs at an extremely low volume fraction of around 0.25%, which is lower than observed (around 3%) with the same particles when charge-stabilized in polar solvent. Furthermore, the nanorod volume fraction at the transition increases with increasing concentration of ligands, in a similar way as in polar media where increasing the ionic strength leads to surface-charge screening. This peculiar system was investigated by dynamic light scattering, Fourier-Transform Infra-Red spectroscopy, zetametry, electron microscopy, polarized-light microscopy, photoluminescence measurements, and X-ray scattering. Based on these experimental data, we formulate several tentative scenarios that might explain this unexpected phase behavior. However, at this stage, its full understanding remains a pending theoretical challenge. Nevertheless, this study shows that dispersing anisotropic nanoparticles in an apolar solvent may sometimes lead to spontaneous ordering events that defy our intuitive ideas about colloidal systems.

In-vivo, real-time study of the local and collective cellular biomechanical responses requires the fine and selective manipulation of the cellular environment. One innovative pathway is the use of photoactive bio-substrates such as azobenzene-containing materials, which exhibit spectacular photomechanical properties, to optically trigger the local, mechanical stimulation of cells. Excited cells exhibit spectacular morphological modifications and area shrinkage, which are dependent on the illumination. This demonstrates the capabilities of photomechanically active substrates to study the phenomena resulting from the mechanical interaction of cells with their environment.

We use europium doped single crystalline NaYF4nanorods for probing the electric and magnetic contributions to the local density of optical states (LDOS). Reciprocically, we determine intrinsic properties of the emitters (oscillator strength, quantum yield) by comparing their measured and simulated optical responses in front of a mirror. We first experimentally determine the specifications of the nanoprobe (orientation and oscillator strength of the electric and magnetic dipoles moments) and show significant orientation sensitivity of the branching ratios associated with electric and magnetic transitions. In a second part, we measure the modification of the LDOS in front of a gold mirror in a Drexhage's experiment. We discuss the role of the electric and magnetic LDOS on the basis of numerical simulations, taking into account the orientation of the dipolar emitters. We demonstrate that they behave like degenerated dipoles sensitive to polarized partial LDOS.

NaYF 4 : Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 μm and light powers down to 10 mW. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective σ and π orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4–5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means.

Cells interact with a chemical and mechanical environment that influences their adaptive response and conditions the physiology and pathophysiology of the tissues. Much effort is being made to reconstruct simple systems in order to study the reciprocal influences of tissues and their environment, as well as to measure the consequences of environmental disturbances on cells. Specific tools are required for the in-vivo, real-time manipulation of the cellular environment’s mechanical properties and for the measurement of the resulting local and collective cellular biomechanical responses. One innovative solution is the use of photoactive systems such as azobenzene-containing polymer materials (azopolymers), whose microstructure and mechanical optical and surface properties can be modulated in time and space by light. Here we show that azopolymer bio-substrates can be used to optically control and study the cellular response of mouse fibroblasts and to single out different classes of cellular responses that might specifically depend on the photo-induced mechanical modification of the environment surrounding the cellular focal adhesions.

Hybrid metal-polymer micropillar arrays are elaborated by solvent-assisted embossing techniques and subsequent gold deposition. The polymer is poly(methyl methacrylate) (PMMA) grafted with Disperse Red 1 (DR1) azobenzene derivatives. This photochromic material exhibits spectacular photomechanical properties. Under off-normal p-polarized illumination in the absorption band of the DR1, the metal-polymer hybrid micropillars bend in a direction determined by the light polarization. The deformation remains stable when the light excitation is turned off. The optically driven modification of the pillar shape allows us to tune the optical properties of the pillar arrays. Very large intensity changes are measured in the diffraction spectra at zero order (specular reflection), first order, and second order, with almost on and off switching of the diffraction efficiency. The photoinduced bending of the micropillars can be fully reversed by switching the linear light polarization to the orthogonal s-polarization state. This allows us to restore the initial optical properties of the pillar array. The polarization-controlled reversibility of the pillar deformation suggests a complex photoinduced deformation mechanism involving stress and stress release assisted by the change in the viscoelastic properties of the polymer under illumination in the absorption band of the DR1 chromophore.

Vertically aligned nanorod assemblies are of great interest both for fundamental studies of anisotropic physical properties arising from the structures and for the development of functional devices utilizing such anisotropic characteristics. Simultaneous measurement of the homeotropic order parameter (Shomeo) of assemblies in dynamic states can allow further optimization of the assembly process and the device performance. Although many techniques (e.g. birefringence measurement, SAXS analysis, and high-resolution microscopy) have been proposed to characterise Shomeo, these do not yet meet the essential criteria such as for rapid, in situ and non-destructive analyses. Here, we propose a novel approach employing a unique photoluminescence behaviour of lanthanide-doped crystalline nanorods, of which the emission spectrum contains the detailed information on the structure of the assembly. We demonstrate a rapid in situ determination of Shomeo of Eu3+-doped NaYF4 nanorods of which the orientation is controlled under an external electric field. The method does not require the consideration of polarization and can be performed using a conventional fluorescence microscopy setup. This new methodology would provide a more in-depth examination of various assembled nanostructures and the collective dynamics of their building blocks.

We demonstrate optical trapping of rare earth-doped NaYF 4 :Er/Yb nanorods of high aspect ratio (length 1.47 μ m and diameter 140 nm) using a quasi Bessel beam (QBB) generated by positive axicon optical fiber tips. Propulsion or trapping of the nanorods is demonstrated using either single or dual fiber nano-tip geometries. The optical force exerted on the trapped nanorods, their velocities, and their positions have been analyzed. We determine the trap stiffness for a single nanorod to be 0.12 pN/ μ m (0.003 pN/ μ m) by power spectrum analysis and 0.13 pN/ μ m (0.015 pN/ μ m) by Boltzmann statistics in the direction perpendicular to (along) the fiber axes for an average optical power of 34 mW. The experiments illustrate the advantage of using a QBB for multiple nanorod trapping over a large distance of up to 30 μ m.

Orientation of nanoscale objects can be measured by examining the polarized emission of optical probes. To retrieve a three-dimensional (3D) orientation, it has been essential to observe the probe (a dipole) along multiple viewing angles and scan with a rotating analyzer. However, this method requires a sophisticated optical setup and is subject to various external sources of error. Here, we present a fundamentally different approach employing coupled multiple emission dipoles that are inherent in lanthanide-doped phosphors. Simultaneous observation of different dipoles and comparison of their relative intensities allow to determine the 3D orientation from a single viewing angle. Moreover, the distinct natures of electric and magnetic dipoles originating in lanthanide luminescence enable an instant orientation analysis with a single-shot emission spectrum. We demonstrate a straightforward orientation analysis of Eu 3+ -doped NaYF 4 nanocrystals using a conventional fluorescence microscope. Direct imaging of the rod-shaped nanocrystals proved the high accuracy of the measurement. This methodology would provide insights into the mechanical behaviors of various nano- and biomolecular systems.

Europium-doped NaYF4 nanorods with a high aspect ratio are optically trapped using a single fibre tip optical tweezers. Three distinct trapping positions of the nanorods are observed: in contact with the fibre tip, close to the tip and 5 mu m from the tip end. The direction and polarisation-dependent Eu3+ photoluminescence is investigated by recording the emission parallel and perpendicular to the nanorod long axis through the trapping fibre and the microscope objective, respectively. These spectroscopic measurements permit an unambiguous determination of the nanorod orientation.

Due to their narrow reflection peak as well as their compact structure, guided mode resonance filters (GMRFs) are attractive for many applications. In this work, we will demonstrate the possibility to modulate the properties of a GMRF by associating it with liquid crystals (LCs). By impregnating the diffraction grating with LCs, it is possible to switch between an active and an inactive state depending on the polarization of the light or the applied voltage. In this paper we fabricated and characterized the first diffraction order of LC-impregnated gratings with different periods (0.8–5.0 µm) and depths (120 and 840 nm) to test the ability of liquid crystals to adjust the diffraction properties. Finally, without voltage, more than 99.8% of initial diffraction could be turned off with a 90° rotation polarization whereas, by applying a voltage of 30 V; 90–99% of the initial diffraction is turned off according to the grating dimensions. The effect of the grating dimension (period, depth) on the diffraction modulation capacity will be discussed.

Rare-earth doped nanocrystals possess optical transitions with significant either electric or magnetic dipole characters. They are of considerable interest for understanding and engineering light-matter interactions at the nanoscale with numerous applications in nanophotonics. Here, we study the ${}^{5}{D}_{0}{\ensuremath{\rightarrow}}^{7}{F}_{1}$ transition dipole vector in individual ${\mathrm{NaYF}}_{4}:{\mathrm{Eu}}^{3+}$ nanorod crystals by Fourier and confocal microscopies. A single-crystal host matrix leads to narrow emission lines at room temperature that permit separation of the Stark sublevels resulting from the crystal-field splitting. We observe a fully magnetic transition and low variability of the transition dipole orientation over several single nanorods. We estimate the proportion of the dipole transitions for the Stark sublevels. We also determine an effective altitude of the rod with respect to the substrate. The narrow emission lines characteristic of ${\mathrm{NaYF}}_{4}:{\mathrm{Eu}}^{3+}$ ensure well-defined electric or magnetic transitions, and are thus instrumental for probing locally their electromagnetic environment by standard confocal microscopy.

Light tunable materials such as azobenzene-containing polymers are nowadays a promising way to achieve optical control of matter up to the nanoscale. In particular, the materials’ optical and mechanical responses can be tuned by controlling the spatial and temporal distribution of the projected light field, which allows to achieve precise, reversible manipulation, in real-time, of the materials’ response. The understanding of the photomechanical phenomena occurring in azopolymers will be discussed as well as their applications as multifunctional materials.

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.

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.

Due to their narrow reflection peak as well as their compact structure, Guided Mode Resonance Filters (GMRFs) are attractive for many applications. We demonstrate the possibility to modulate the properties of a GMRF by associating with liquid crystals (LCs). By impregnating the diffraction grating with LCs, it is possible to switch between an active and an inactive state depending on the polarization of the light or the applied voltage. In this paper we fabricated and characterized the first diffraction order of LC-impregnated gratings with different periods (0,8 to 5,0μm) and depths (130 to 840nm) to test the ability of liquid crystals to adjust the diffraction properties. Finally, 99.8% of diffraction turn off with a 90° rotation polarization at zero voltage and 90 to 99% by applying a voltage of 30 V according to the grating dimensions. The effect of the grating dimension on the diffraction modulation capacity will be discussed.

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.

Silicon electrodes represent a great potential on increasing the energy density of Li-ion batteries, but stabilization during cycling is an important issue to be solved for enabling a reliable application. Such stabilization has been sought for by surface grafting of hydrogenated amorphous silicon (a-Si:H) electrodes. Grafting a molecular monolayer of carboxydecyl moieties (acid grafting) or poly(oxoethylene) (PEG) chains decreases the irreversible capacity and stabilizes the solid-electrolyte interphase (SEI) on a-Si:H. FTIR spectroscopy confirms a breathing behavior of the SEI layer at each step of charge/discharge through in-situ experiments, but also shows that acid grafting reduces this behavior to a large extent. In this way, acid grafting decreases the amount of charge irreversibly consumed for the formation of a spontaneous SEI and stabilizes the SEI along the electrochemical cycles.

Azobenzene molecules are well known for their photoswitching properties. When incorporated into a polymer film, push−pull azobenzene derivatives such as the DR1 (Dispersed Red 1) confer to the film some remarkable photomechanical properties, allowing for the direct optical inscription of relief patterns. While mainly investigated in the case of organic polymers such as poly(methyl methacrylate) (PMMA), it was shown some years ago that similar photoinduced deformation phenomena could occur in materials using sol‐gel silica as a host matrix. In the present study, the process is revisited, showing that photopatterning can be drastically improved through a careful control of the rheology of the sol‐gel film. Increase in the photoinscribed relief pattern amplitude by up to a factor of three to four is thus achieved. In the second step, it is also shown that sol‐gel silica matrix offers the possibility of removing all organic compounds from the film after photostructuration, without any relaxation of the patterns. This opens the way toward the use of sol‐gel azo/silica films for the elaboration of micro and nanostructured transparent silica coatings that could be used for many applications among which there is light extraction management in light emitting devices.