Gestion de la lumière dans des couches luminescentes nanostructurées : application aux diodes blanches

In order to create white light, a blue diode can be associated with phosphors, which convert a part of the blue light to a visible light presenting a lower energy. Usually, micron size phosphors are used as down-converter: the reference phosphor for this application is the doped oxide YAG:Ce. The phosphor size is larger than the wavelength, making the converter layer scatter, which helps to extract the emitted light outside of the high refractive index layer. Nevertheless, this extraction is not well controlled and leads to energy losses. We aim at diminishing these losses associated with scattering by using converter layers based on nanoparticles instead of micron size phosphors. In order to control the extraction of the light that is guided in the non diffusive converter layer, the dielectric microstructure of the matrix which contains the phosphors nanoparticles must be optimized. First, we demonstrate on model layers, consisting in a sol-gel matrix doped with molecular emitters, the ability to extract the light guided in a luminescent layer with an appropriated periodic patterning of its surface. A 10 factor has been obtained at small angles, which corresponds to a 5 factor when integrating over all angles. Then, we develop YAG:Ce nanoparticles with optimized optical properties. A protected annealing process is employed, which allows improving the photostability and the quantum yield of the nanoparticles, while still preserving their small size and their good dispersion state. Finally, particles are incorporated in transparent layers in order to create converter layers, which then have been deposited on white LEDs.Dans le but de générer de la lumière blanche, une diode bleue peut être associée à des luminophores qui convertissent une partie de la lumière bleue de la diode en une lumière visible de plus basse énergie. Classiquement, cette conversion de lumière est assurée par des luminophores de taille micronique, du YAG:Ce le plus souvent. Compte tenu de la taille des luminophores, ces couches sont diffusantes, ce qui favorise l'extraction hors de la couche haut-indice de la lumière émise. Mais cette extraction n'est pas contrôlée et entraîne des pertes d'énergie. Afin de diminuer ces pertes dues à la diffusion, notre stratégie consiste à réaliser des couches de conversion de lumière à base de nanoparticules au lieu des luminophores microniques classiquement utilisés. Pour pouvoir prévoir et contrôler complètement l'extraction de la lumière alors guidée dans la couche de conversion transparente, la microstructure diélectrique de la matrice contenant les nanoparticules doit être optimisée. Dans un premier temps, nous avons mis en évidence, sur des couches modèles composées d'une matrice sol-gel contenant des luminophores moléculaires, la possibilité d'extraire la lumière piégée dans une couche luminescente par une structuration périodique adéquate de sa surface. Un facteur 10 d'extraction a notamment été obtenu aux petits angles, correspondant à un facteur 5 en intégrant sur tous les angles. Nous avons ensuite développé des nanoparticules de YAG:Ce dont les propriétés optiques ont été optimisées pour se rapprocher de celles du matériau massif. Une procédure de recuit protégé a notamment été développée, permettant d'améliorer considérablement la photostabilité et le rendement interne des nanoparticules tout en conservant leur petite taille et leur bon état de dispersion. Enfin les particules ont été incorporées dans des couches transparentes afin de réaliser des couches de conversion de lumière, qui ont ensuite été déposées sur des diodes bleues

Gestion de la lumière dans des couches luminescentes nanostructurées (application aux diodes blanches)

Dans le but de générer de la lumière blanche, une diode bleue peut être associée à des luminophores qui convertissent une partie de la lumière bleue de la diode en une lumière visible de plus basse énergie. Classiquement, cette conversion de lumière est assurée par des luminophores de taille micronique, du YAG:Ce le plus souvent. Compte tenu de la taille des luminophores, ces couches sont diffusantes, ce qui favorise l'extraction hors de la couche haut-indice de la lumière émise. Mais cette extraction n'est pas contrôlée et entraîne des pertes d'énergie. Afin de diminuer ces pertes dues à la diffusion, notre stratégie consiste à réaliser des couches de conversion de lumière à base de nanoparticules au lieu des luminophores microniques classiquement utilisés. Pour pouvoir prévoir et contrôler complètement l'extraction de la lumière alors guidée dans la couche de conversion transparente, la microstructure diélectrique de la matrice contenant les nanoparticules doit être optimisée. Dans un premier temps, nous avons mis en évidence, sur des couches modèles composées d'une matrice sol-gel contenant des luminophores moléculaires, la possibilité d'extraire la lumière piégée dans une couche luminescente par une structuration périodique adéquate de sa surface. Un facteur 10 d'extraction a notamment été obtenu aux petits angles, correspondant à un facteur 5 en intégrant sur tous les angles. Nous avons ensuite développé des nanoparticules de YAG:Ce dont les propriétés optiques ont été optimisées pour se rapprocher de celles du matériau massif. Une procédure de recuit protégé a notamment été développée, permettant d'améliorer considérablement la photostabilité et le rendement interne des nanoparticules tout en conservant leur petite taille et leur bon état de dispersion. Enfin les particules ont été incorporées dans des couches transparentes afin de réaliser des couches de conversion de lumière, qui ont ensuite été déposées sur des diodes bleuesIn order to create white light, a blue diode can be associated with phosphors, which convert a part of the blue light to a visible light presenting a lower energy. Usually, micron size phosphors are used as down-converter: the reference phosphor for this application is the doped oxide YAG:Ce. The phosphor size is larger than the wavelength, making the converter layer scatter, which helps to extract the emitted light outside of the high refractive index layer. Nevertheless, this extraction is not well controlled and leads to energy losses. We aim at diminishing these losses associated with scattering by using converter layers based on nanoparticles instead of micron size phosphors. In order to control the extraction of the light that is guided in the non diffusive converter layer, the dielectric microstructure of the matrix which contains the phosphors nanoparticles must be optimized. First, we demonstrate on model layers, consisting in a sol-gel matrix doped with molecular emitters, the ability to extract the light guided in a luminescent layer with an appropriated periodic patterning of its surface. A 10 factor has been obtained at small angles, which corresponds to a 5 factor when integrating over all angles. Then, we develop YAG:Ce nanoparticles with optimized optical properties. A protected annealing process is employed, which allows improving the photostability and the quantum yield of the nanoparticles, while still preserving their small size and their good dispersion state. Finally, particles are incorporated in transparent layers in order to create converter layers, which then have been deposited on white LEDs.PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Novel technologies for transdermal drug delivery: combination of microneedles and iontophoresis

International audienceThis PhD project is willing to develop a prototype of wearable device combining two transdermal drug delivery (TDD) technologies: iontophoresis (ITP) and microneedles (MN). ITP was used as an active delivery technique helping heavy molecules migrate faster and deeper through the effect of a small current. Screen-printed Ag/AgCl electrodes were prepared to provide a leightweight, low cost and conformable device. Injection molded poly-L-lactic acid (PLLA) hollow MN were placed on top of the anode, or the positive electrode. Fluorescein isothiocyanate-labelled bovine serum albumin (FITC-BSA) was used as a drug model and followed by fluorimetry. Eventually, insulin will be used in delivery experiments. For both ITP electrodes and MN, fabrication processes involved are suitable for industrial scale-up

Novel technologies for transdermal drug delivery: combination of microneedles and iontophoresis

International audienceThis PhD project is willing to develop a prototype of wearable device combining two transdermal drug delivery (TDD) technologies: iontophoresis (ITP) and microneedles (MN). ITP was used as an active delivery technique helping heavy molecules migrate faster and deeper through the effect of a small current. Screen-printed Ag/AgCl electrodes were prepared to provide a leightweight, low cost and conformable device. Injection molded poly-L-lactic acid (PLLA) hollow MN were placed on top of the anode, or the positive electrode. Fluorescein isothiocyanate-labelled bovine serum albumin (FITC-BSA) was used as a drug model and followed by fluorimetry. Eventually, insulin will be used in delivery experiments. For both ITP electrodes and MN, fabrication processes involved are suitable for industrial scale-up

Relaxation visqueuse en géométrie confinée de nanostructures embossées dans du PMMA.

La structuration de couches de polymère par nano-impression à chaud est une technique qui présente aujourd’hui de nombreux avantages. Les conditions d’embossage et la relaxation des structures restent encore des sujets de recherche importants. Nous nous sommes intéressés à la relaxation d’une couche de PMMA chauffée au-dessus de la Tg. La réalisation d’expériences et l’élaboration d’un modèle nous ont permis de mettre en évidence l’effet du confinement sur l’écoulement

Lambert W-function based modelling of P-OTFTs and application to low temperature measurements

International audienceIn this paper, a physically-based model was adapted to P-type organic thin-film transistors (P-OTFTs) by describing the accumulation charge with a Lambert W (LW) function in order to extract their figures of merit as threshold voltage, low-field mobility and subthreshold slope related to the interface traps density. This continuous and differentiable model, implemented for the first time on OTFTs, allows an accurate evaluation of the output and transfer characteristics, reproducing well the OTFT behaviour below and above the threshold region. Additionally, it was validated for different channel lengths (from 10 to 100 μm), taking into account short-channel effects. This model was also used to extract the parameters of P-OTFTs measured at low temperatures, showing a thermally activated transport in the polymer organic semiconductor (OSC) with an effective width of localized states around 90 meV and a relatively high band-like mobility. We also showed that the evolution of the threshold voltage versus temperature was related to the electrostatic effect of the interface trapped charge. The comparison between classical extraction methods and our LW-function based method validated the application of our model to P-OTFTs parameters extraction, opening a possibility for compact modelling

Electrical and mechanical properties of intrinsically flexible and stretchable PEDOT polymers for thermotherapy

International audienceFor wearable applications such as electronic skin and biosensors, stretchable conductors are required (∼30% strain to follow the skin extension). Owing to its high conductivity, good flexibility, low cost, and ease of processing, poly(3,4-ethylenedioxythiophene) (PEDOT) appears as a promising candidate. However, destructive cracks come out above 10% strain in the case of PEDOT:PSS, the most common form of PEDOT. Different strategies have already been investigated to solve this problem, including the design of specific structures or the addition of plasticizers. This article presents a different approach to obtain highly conductive and stretchable PEDOT materials based on doping with small counteranions. We indeed demonstrate the intrinsic stretchability (up to 30% strain) of thin films (35 nm) of PEDOT-based materials with small counterions. Both thin-PEDOT:OTf (triflate counter-ion) and thin-PEDOT:Sulf (sulfate counter-ion) films remain structurally resilient up to 25–30% strain, and their electrical conductivity remains remarkably stable over more than 100 cycles. Under limited strain (<30%), polarized UV–vis–NIR measurements (parallel and perpendicular to the stretching direction) show that the conductivity of the material is improved by chain alignment in the stretching direction. As a proof of concept, a thermotherapy patch is presented. It shows a fine temperature control (stability around 40 °C at 9 V bias) and a uniform heating across the surface

Electrochemical sensors for animal welfare

Session "Biomedical sensors & diagnostics"International audienceWAIT4 (Welfare: Artificial Intelligence and new Technologies for Tracking Key Indicator Traits in Animals Facing Challenges of the Agro-ecological Transition) project aims at increasing research-based capacities to quantify and characterize animal welfare (AW) in the agro-ecological (AE) perspective and revising farming practices by considering interactions between the animal and its environment. In this perspective, the development of new sensors for assessing the kinetics of physiological variables of interest (Na+, K+, pH) in animals Interstitial Fluid (ISF) by microneedles patch will be a valuable aid for farmers to monitoring AW states and various stressors

The formation of polymer-dopant aggregates as a possible origin of limited doping efficiency at high dopant concentration

International audienc

Low temperature measurements on organic thin film transistors

session poster (L.1.25)International audienc