Sol-gel derived ionic copper-doped microstructured optical fiber: a potential selective ultraviolet radiation dosimeter

International audienceWe report the fabrication and characterization of a photonic crystal fiber (PCF) having a sol-gel core doped with ionic copper. Optical measurements demonstrate that the ionic copper is preserved in the silica glass all along the preparation steps up to fiber drawing. The photoluminescence results clearly show that such an ionic copper-doped fiber constitutes a potential candidate for UV-C (200-280 nm) radiation dosimetry. Indeed, the Cu+-related visible photoluminescence of the fiber shows a linear response to 244 nm light excitation measured for an irradiation power up to 2.7 mW at least on the Cu-doped PCF core. Moreover, this response was found to be fully reversible within the measurement accuracy of this study ( ± 1%), underlying the remarkable stability of copper in the Cu+ oxidation state within the pure silica core prepared by a sol-gel route. This reversibility offers possibilities for the achievement of reusable real-time optical fiber UV-C dosimeters

In situ synthesis of highly crystalline Tb-doped YAG nanophosphor using the mesopores of silica monolith as template

International audienceThis report describes the first synthesis of a highly crystalline YAG:Tb nanophosphor inside the pores of a mesoporous silica monolith (MSM). A simple wet impregnation procedure using a YAG:Tb sol and a MSM platform prepared by a sol–gel method was adopted to prepare highly homogeneous MSM–YAG:Tb luminescent composites. The morphological, structural and luminescence properties of in situ generated YAG:Tb nanocrystals, investigated using XRD, TEM, HRTEM, EDS, FTIR, nitrogen gas sorption and photoluminescence measurements, were compared to those of the bulk YAG:Tb phosphor. The specific surface area and the pore volume of the MSM host material were found to be lower when YAG:Tb nanoparticles were grown in the pores of the MSM material. The particle diameter of the nano-sized YAG:Tb phosphor was estimated to be about 23 nm. The MSM–YAG:Tb composite exhibited a strong green fluorescence emission with the characteristic main emission band of Tb3+ located at 548 nm. The prepared composite also showed a shorter photoluminescence (PL) lifetime and excitation bands shifted to lower wavelengths compared to the neat YAG:Tb phosphor. The as-prepared MSM–YAG:Tb material could be integrated into optoelectronic devices and holds good potential to be applied in decorative lightin

Contribution of weak localization and electron-electron interaction, in corrective term “mT1/2” of the metallic conductivity in n-type SiAs

We present measurements of the electrical conductivity of barely metallic n-type SiAs that are driven to the metal-insulator transition (MIT) by impurity concentration. The experiments were carried out at low temperature in the range (3.48 - 0.00044 K) and with impurity concentrations up to . On the metallic side of the MIT, the electrical conductivity is found to behave likedown to 0.44 mK. Physical explanation to the temperature dependence of the conductivity is given in metallic side of the MIT using a competition between two effects involved in the mechanisms of conduction, like electron-electron interaction effect, and weak localization effect

Plastic strain accommodation and acoustic emission during melting of embedded particles

Melting point phenomena of micron-sized indium particles embedded in an aluminum matrix were studied by means of acoustic emission. The acoustic energy measured during melting increased with indium content. Acoustic emission during the melting transformation suggests a dislocation generation mechanism to accommodate the 2.5% volume strain required for melting of the embedded particles. A geometrically necessary increase in dislocation density of 4.1 x 10^13 m^-2 was calculated for the 17 wt% indium composition.Comment: 4 pages, 3 figures, 1 tabl

Oak root response to ectomycorrhizal symbiosis establishment: RNA-Seq derived transcript identification and expression profiling

Ectomycorrhizal symbiosis is essential for the life and health of trees in temperate and boreal forests where it plays a major role in nutrient cycling and in functioning of the forest ecosystem. Trees with ectomycorrhizal root tips are more tolerant to environmental stresses, such as drought, and biotic stresses such as root pathogens. Detailed information on these molecular processes is essential for the understanding of symbiotic tissue development in order to optimize the benefits of this natural phenomenon. Next generation sequencing tools allow the analysis of non model ectomycorrhizal plant-fungal interactions that can contribute to find the "symbiosis toolkits" and better define the role of each partner in the mutualistic interaction. By using 454 pyrosequencing we compared ectomycorrhizal cork oak roots with non-symbiotic roots. From the two cDNA libraries sequenced, over 2 million reads were obtained that generated 19,552 cork oak root unique transcripts. A total of 2238 transcripts were found to be differentially expressed when ECM roots were compared with non-symbiotic roots. Identification of up- and down-regulated gens in ectomycorrhizal roots lead to a number of insights into the molecular mechanisms governing this important symbiosis. In cork oak roots, ectomycorrhizal colonization resulted in extensive cell wall remodelling, activation of the secretory pathway, alterations in flavonoid biosynthesis, and expression of genes involved in the recognition of fungal effectors. In addition, we identified genes with putative roles in symbiotic processes such as nutrient exchange with the fungal partner, lateral root formation or root hair decay. These findings provide a global overview of the transcriptome of an ectomycorrhizal host root, and constitute a foundation for future studies on the molecular events controlling this important symbiosis.This work was funded by the Portuguese Foundation for Science and Technology (www.fct.pt) in the frame of the project Cork Oak EST Consortium SOBREIRO/0034/2009. Post-doc grant to MS was supported by the Portuguese Foundation for Science and Technology (SFRH/BPD/25661/2005). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Élaboration par voie sol-gel et étude structurale de verres de silice destinés à la fabrication de fibres microstructurées

LILLE1-BU (590092102) / SudocSudocFranceF

Élaboration et caractérisation de couches minces vitreuses dopées par des nano-particules semi-conductrices

Ce travail concerne la recherche de nouvelles solutions pour l'optique non-linéaire intégrée. Les verres dopés par des nanoparticules semi-conductrices constituent un exemple de matériaux dont les potentialités en optique non-linéaIre sont depuis longtemps reconnues, quoique non encore exploitées. Les effets dus au confinement confèrent aux nanoparticules des propriétés physiques spécifiques par rapport à celles de la phase massive. Le mouvement des porteurs de charge dans une nanoparticule étant limité par le volume, l'énergie cinétique devient discrète et les niveaux s'écartent les uns des autres. C'est cette propriété de discrétisation des niveaux, associée à l'élargIssement du gap semi-conducteur, qui peut être exploitée en optique non-linéaire. Afin de conférer à ces guides d'onde des propriétés optiques non-linéaires, nous avons dopé le sol de TiO2 avec des nanoparticules de CdS ou de PbS produits par la méthode colloïdale des ligands de surface. Nous avons optimisé les paramètres de synthèse de couches minces sol-gel de TiO2 optiquement guidantes, non dopées et dopées avec des nanoparticules de CdS ou de PbS. Les films minces recuits à 100 ou 200C sont homogènes, exempts de craquelures mais guident la lumière avec une forte atténuation (1 à 1,5 dB/cm). En solution, les nanocristaux produits par une méthode colloïdale présentent une distribution de taille étroite avec un diamètre moyen contrôlé entre 3 et 6 nm. Nous avons observé le ralentissement de leur croissance par la matrice TiO2 et une stabilisation de la solution. L'indice non-linéaire n2 des solutions, mesuré par technique Z-scan, vaut environ -2x10-18 m2/W, valeur comparable à celles reportées dans la littérature. Pour un film TiO2 dopé CdS (30%) et traité à 500C, l'absorption induite mesurée (b = 16x10-7m/W) est de plusieurs ordres de grandeur supérieure à celle du cristal massif, ce qui est relié aux nombreux niveaux de défauts. Par la technique de pulvérisation radiofréquence, nous avons déposé des nanoparticules d'InSb dans des couches minces de silice et utilisé 2 types de protocole pour leur traitement thermique. Les mesures de non-linéarité on révélé un coefficient d'absorption induite b également bien supérieur à celui d'lnSb massif. On a mis en évidence l'influence du régime continu ou lmpulsionnel des lasers sur les propriétés du matériau.LILLE1-BU (590092102) / SudocSudocFranceF

Ice mixtures formed by simultaneous condensation of formaldehyde and water: an in situ study by micro-Raman scattering

International audienc

Vitrocéramiques nano-structurées SiO2-SnO2 sous forme de monolithes et de guides d'ondes planaires élaborés par voie sol-gel (caractérisation structurale et activation par des ions de terres rares)

L avènement de sources lumineuses performantes et compactes à base de silice dopée par des ions de terres rares (TR) passe par l obtention de rendements d émission élevés, ce qui nécessite une bonne dispersion de ces ions. Les vitrocéramiques, associant une matrice vitreuse avec des nanocristaux (NC), permettent une telle dispersion et fournissent néanmoins une transparence optique adéquate. D autre part, les NC présentent une absorption de lumière spectralement large et peuvent transférer leur énergie vers les ions de TR pour améliorer l efficacité d émission.Dans ce travail, des vitrocéramiques à base de silice contenant des NC de SnO2 ont été élaborées sous forme de couches minces et de massifs par la technique sol-gel. Les propriétés optiques et structurales des systèmes sous forme de couches minces ont été comparées à celles des systèmes massifs. Plusieurs paramètres, tels que la concentration maximale d étain, les températures de cristallisation et de densification, diffèrent selon la morphologie des matériaux. L influence réciproque entre la matrice de silice et les NC de SnO2 a été étudiée par l utilisation conjointe de plusieurs techniques d analyses telles que les spectroscopies vibrationnelles, la DRX, la MET, la porosimétrie BET L ajout d étain retarde la densification de la matrice, laissant une porosité résiduelle.La luminescence des ions Er3+ et Eu3+ (largeur de bande d émission, durée de vie) a montré clairement l existence de 2 types de sites hôtes, l un cristallin et l autre amorphe. Enfin, les NC de SnO2 favorisent la dispersion des ions de TR, conduisant à des durées de vies encourageantes et à un transfert d énergie entre cristal et TR.The obtention of efficient and compact light sources based on silica doped with rare earth (RE) ions demands high emission yields, which require a good dispersion of RE ions. Glass-ceramics, associating a glass with nanocrystals (NCs), allow such a dispersion and still assure adequate optical transparency. In addition, the NCs have broad absorption bands and can transfer their energy to the RE ions, thus improving the emission efficiency. In this work, silica-based ceramics containing SnO2 NCs were prepared as thin films and bulk by the sol-gel technique. The optical and structural properties of the thin films were compared with those of monoliths. Several parameters, such as the maximum concentration of tin, the temperature of crystallization and of densification, differ according to the morphology of the materials. The interaction between the silica matrix and SnO2 NCs was studied by combining several analytical techniques such as vibrational spectroscopies, XRD,TEM, porosimetry BET The addition of tin retards the densification of the matrix, leaving a residual porosity. The luminescence of Er3+ and Eu3+ (emission bandwidths, lifetimes) clearly shows the existence of two types of host sites, one crystalline and the other amorphous. Finally, the SnO2 NCs promote the dispersion of the RE ions, leading to longer lifetimes and an energy transfer between crystal and RE.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF