Caractérisation spectroscopique et modélisation de l'effet de la porosité, de la densification et du dopage sur la structure de gels de silice

Ce travail concerne l'étude de l'influence de plusieurs paramètres sur les processus de densification de gels de silice, notamment les effets de la porosité, d'un dopage et de la composition d'une matrice vitreuse binaire. Le but de cette étude est de contribuer à la compréhension de l'effet de ces paramètres sur les propriétés structurales en vue de des applications potentielles dans les domaines optique et biologique. La spectroscopie de diffusion Raman et les mesures texturales par la méthode B.E.T ont pu montrer que les cinétiques de densification de gels de silice poreux à porosité contrôlée était inversement proportionnelle à la porosité initiale des gels. De plus, l'incorporation d'ions métalliques modifie de façon importante les cinétiques de densification. Un post-dopage par des ions Ag+ réduit d'un facteur quatre-vingt le temps nécessaire pour obtenir l'état dense alors que le temps est augmenté d'un facteur deux environ, pour les ions Ce3+.La spectroscopie de diffusion Raman en configuration guidée a été utilisée pour caractériser la structure de guides d'onde germanosilicates. En utilisant l'ion Eu3+ comme sonde luminescente, nous avons pu décrire l'environnement de cet ion dans la matrice germanosilicate. Il a été montré qu'un système riche en germanium conduit à un environnement plus souple autour des ions europium avec des distances europium-oxygène plus grandes. Ces résultats ont été confirmés lors de simulation numérique par dynamique moléculaire. Par ailleurs, il a été montré les systèmes germanosilicates sont constitués d'unités SiO4 et GeO4 réparties de façon homogène dans la matrice et les ions Eu3+ sont toujours entourés préférentiellement par 6 ou 7 atomes d'oxygène.LILLE1-BU (590092102) / SudocSudocFranceF

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

CO2 laser–induced precipitation of semiconductor nanoparticles in a dense glass

International audienceNanostructures based on II-VI semiconductor nanocrystallites (NCs) embedded in glass have been studied for many years. Among these systems, the pseudo-binary CdSxSe1-x nanostructures are of particular interest, owing to their optical absorption and emission spectra that cover the entire visible spectral region. Laser irradiation methods have been shown to allow the local growth of several types of NCs in various kinds of matrices. Unfortunately, in the case of the CdSxSe1-x doped silicate glasses, a near-infrared fs laser irradiation, instead of nucleating NCs, leads to permanent refractive index changes in micro-size regions within the glass and may even provoke glass damages at the highest pulse energies. A novel method allowing the local growth of semiconductor nanoparticles in dense silicate glasses is presented. In this method, combining a continuous middle-infrared laser irradiation and a heat-treatment in open air, a transparent melt-quenched borosilicate glass containing CdSxSe1-x nanocrystals was annealed at a temperature below the softening point. Simultaneously, a continuous infrared laser irradiation at 10.6 µm was applied, acting as a thermal addition. Spectroscopic studies reveal the local growth of CdSxSe1-x nanoparticles, with a homogeneous composition and average particle radii ranging from 1.9 to 5.5 nm. These results demonstrate the feasibility of coupling a laser irradiation with an appropriate heat-treatment in order to achieve the spatial organization

CO2 laser-induced precipitation of CdSxSe1−x nanoparticles in a borosilicate glass: A new approach for the localized growth of quantum dots

International audienceA novel method allowing the local growth of semiconductor nanoparticles in dense silicate glasses is presented. In this method combining a continuous middle-infrared laser irradiation and a heat-treatment in open air, a transparent melt-quenched borosilicate glass containing CdSxSe1−x nanocrystals was annealed at a temperature below the softening point. Simultaneously, a continuous infrared laser irradiation at 10.6 μm was applied, acting as a thermal addition. Resonant Raman, photoluminescence and absorption spectra reveal the local growth of CdSxSe1−x nanoparticles, with a homogeneous composition and average particle radii ranging from 1.9 to 5.5 nm. These results demonstrate the feasibility of coupling a laser irradiation with an appropriate heat-treatment in order to achieve the spatial organization of nanostructures in vitreous materials

Building nanoparticles in a matrix with a laser: several examples

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Impact of a preoperative pharmaceutical consultation in scheduled orthopedic surgery on admission: a prospective observational study

International audienceBackground. Medication errors have a high prevalence in surgery and management of home medication is strongly involved in these errors. In scheduled surgery, the preoperative consultation is a privileged time to inform the patient about the management of her/his home medication before admission. This study assessed the impact of a pre-anesthesia best possible medication history (PA-BPMH) on admission. The PA-BPMH was performed by a clinical pharmacist prior to the anesthesia consultation for anesthesiologists to prescribe admission medical orders for scheduled orthopedic surgery patients. Methods.This was a prospective observational study which was carried out in an orthopedic surgery department. All patients over 18 years old with an elective orthopedic surgery were eligible except ambulatory surgery patients. The pharmacist registered the PA-BPMH into the software making it available for anesthesiologists for the pre-admission medication order. Finally, a medication reconciliation was performed at admission. The main outcome was the percentage of patients with at least one unintended medication discrepancy (UMD) at admission. The nature, potential clinical impact and acceptance rate of each UMD detected were assessed. Also, the PA-BPMH process was described and patients and anesthesiologists satisfaction was evaluated. Results. A total of 455 patients had a pharmaceutical consultation. Medication reconciliation was performed at admission for 360 patients. Overall, at least one UMD was observed in 13.0% of patients ( n = 47). A total of 63 UMD were detected. The most common type of UMD was omission (25.4%) and incorrect drug (23.8%).Two UMD (3.2%) were evaluated as life threatening. All the UMD detected were corrected on the admission medication order. Conclusion. A preoperative pharmacist-anesthesiologist teamwork seems to improve the safety of perioperative management of home medication for scheduled orthopedic surgery patients. This process needs a randomized clinical trial across a wider range of surgeries before its implementation

H2-induced copper and silver nanoparticle precipitation inside sol-gel silica optical fiber preforms

Ionic copper- or silver-doped dense silica rods have been prepared by sintering sol-gel porous silica xerogels doped with ionic precursors. The precipitation of Cu or Ag nanoparticles was achieved by heat treatment under hydrogen followed by annealing under air atmosphere. The surface plasmon resonance bands of copper and silver nanoparticles have been clearly observed in the absorption spectra. The spectral positions of these bands were found to depend slightly on the particle size, which could be tuned by varying the annealing conditions. Hence, transmission electron microscopy showed the formation of spherical copper nanoparticles with diameters in the range of 3.3 to 5.6 nm. On the other hand, in the case of silver, both spherical nanoparticles with diameters in the range of 3 to 6 nm and nano-rods were obtained

Photo-assisted growth of semiconductor nanostructures in silica matrices

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Methods for doping xerogels, glasses and fibers with metal or semiconductor nanoparticles

International audienc

Verres de silice élaborés par voie sol-gel et destinés à la réalisation de fibres optiques micro/nano-structurées

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