Dosimetric features of strontium orthosilicate (Sr2SiO4) doped with Eu2+

Poster zaprezentowany na miedzynarodowej konferencji naukowej 1st International Conference on Dosimetry and its Applications, Prague, Czech Republic, 23-28 June 2013; w formie artykułu, po recenzjach został przyjęty do druku w Radiation Physics and Chemistry (2014); DOI: 10.1016/j.radphyschem.2014.05.043Thermoluminescence (TL) of strontium orthosilicate doped with Eu2+ has been investigated in the range RT- 750 K. Trap parameters of a TL peak at 450 K established by means of glow curve analysis suggest the possibility of applying this sensitive peak for TL dosimetry. The thermal stability test shows that the 450 K peak is partially unstable. The isothermal decay experiments reveal that the traps responsible for this peak can be emptied by a competitive way that is efficient during storage at a constant temperature, and is characterized by lower values of activation energy and frequency factor

Elaboration and Characterisation of siliceous functionalized materials with controlled structure and texture as models for the study of the surface reactivity and the adsorption of heavy metal cations

Le but de ce travail est l'élaboration d'adsorbants modèles pour l'étude de la réactivité de surface et des phénomènes d'adsorption de cations métalliques à l'interface solide solution aqueuse. L'un des critères de choix de tels adsorbants est la répartition superficielle d'une charge électrique et à l'évolution de cette charge en milieu aqueux. Dans cet objectif, des silices mésoporeuses (SBA-15) fonctionnalisées par insertion contrôlée et en cours de synthèse d'hétéroatomes (Al, Zr, Ti) ont été préparées grâce à une sélection affinée de réactifs et à l'optimisation des conditions de synthèse et de traitement postérieurs (hydrothermal, micro-ondes, variation de pH, ). Une caractérisation approfondie de ces solides (morphologie, texture, propriétés superficielles) a permis de trouver le lien entre l'étape de préparation et la modulation des caractéristiques des adsorbants finaux. Cette caractérisation a fait appel aux méthodes classiques comme l'étude du réseau poreux par adsorption-désorption d'azote, l'analyse de la structure solide par la diffraction de rayons X et l'analyse élémentaire. Par ailleurs, les spectroscopies Raman, UV-Vis, FTIR ont permis d'évaluer le degré d'insertion des hétéroatomes, leur répartition et d'analyser de la nature des groupements OH de surface. Enfin les méthodes d'adsorption et de désorption, avec les techniques de calorimétrie associées en phases gaz et liquide avec l'utilisation de diverses molécules sondes (NH3, Butanol, H+/OH-) ont donné accès aux propriétés superficielles. Les isothermes d'adsorption d'ions ont montré les potentialités de ces solides en tant qu'adsorbant pour le traitement d'effluents liquides.This work deals with the development of model adsorbents for the study of surface reactivity and the adsorption of metal cations at the Solid-Liquid interface. One of the selection criteria for such adsorbents is an adequate surface distribution of the electric charge and its evolution in aqueous media. With this objective in mind, mesoporous silicas (SBA-15) functionalized by the controlled insertion of heteroatom (Al, Zr, Ti) during synthesis were prepared with an effort to select carefully the reagents and to optimize the synthesis and post-treatment conditions (hydrothermal treatment, microwave, pH variation, catalyst use, scaling up of the optimized synthesis). The advanced characterization of these solids (morphology, texture, surface properties) allowed establishing the relationship between the synthesis conditions and the modulation of the properties in the final adsorbents. The characterization methods included the study of the porous network using nitrogen adsorption-desorption, the analysis of the solid structure by X-Ray diffraction and the chemical analysis, as well as the evaluation of the degree of heteroatom insertion, its distribution and the analysis of the nature of surface OH groups with the aid of Raman, UV-Vis, and FTIR spectroscopies. Finally, the adsorption-desorption techniques in conjunction with calorimetry making use of various molecular probes (NH3, Butanol, H+/OH-) in gas and liquid phase provided valuable information about the surface properties. Measurements of the adsorption of ions gave indications for the potential uses of these materials as adsorbents for the liquid waste decontamination.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Morphology Regulation Mechanism and Enhancement of Photocatalytic Performance of BiOX (X = Cl, Br, I) via Mannitol-Assisted Synthesis

BiOX (X = Cl, Br, I) photocatalysts with dominant (110) facets were synthesized via a mannitol-assisted solvothermal method. This is the first report on the exposed (110) facets-, size-, and defects-controlled synthesis of BiOX achieved by solvothermal synthesis with mannitol. This polyol alcohol acted simultaneously as a solvent, capping agent, and/or soft template. The mannitol concentration on the new photocatalysts morphology and surface properties was investigated in detail. At the lowest concentration tested, mannitol acted as a structure-directing agent, causing unification of nanoparticles, while at higher concentrations, it functioned as a solvent and soft template. The effect of exposed (110) facet and surface defects (Bi(3−x)+, Bi4+, Bi5+) of BiOX on the photocatalytic activity of nanomaterials under the UV–Vis irradiation were evaluated by oxidation of Rhodamine B (RhB) and 5-fluorouracil (5-FU), an anticancer drug, and by reduction of Cr(VI). Additionally, the influence of crucial factors on the formation of BiOX in the synthesis with mannitol was discussed extensively, and the mechanism of BiOX formation was proposed. These studies presented a new simple method for synthesizing BiOX without any additional surfactants or shape control agents with good photocatalytic activity. The study also provided a better understanding of the effects of solvothermal conditions on the BiOX crystal growth

Optical processes in YVO4: Eu3+ across zircon-to-scheelite phase transition.

International audienceThe luminescence processes across zircon-to-scheelite phase transition in undoped YVO4 and Eu3+-doped YVO4 are investigated by measuring the Raman, excitation and emission spectra and decay characteristics of the compounds with respect to high hydrostatic pressure up to 200 kbar. The scheelite polymorphs obtained after releasing the high pressure show no luminescence when undoped, even down to 10 K, but when activated with Eu3+ exhibit the characteristic scheelite-related Eu3+ emission but with low intensity. This emission is produced upon UV excitation in zircon inclusions that remain after the pressure treatment

Binding energies of Eu2+Eu^{2+} and Eu3+Eu^{3+} ions in \betha-Ca2SiO4Ca_{2}SiO_{4} doped with europium

β-Ca2SiO4 doped with Eu2+and Eu3+was synthesized by solid state reaction. Europium replaces Ca2+ ions either as Eu2+ or Eu3+, both occupying two not equivalent sites; seven fold and eight fold coordinated by O2−. β-Ca2SiO4:Eu2+, β-Ca2SiO4:Eu3+ and β-Ca2SiO4:Eu2+, Eu3+ samples were investigated by structural and spectroscopic methods. Specifically it has been shown that luminescence spectra of the β-Ca2SiO4:Eu2+, Eu3+ system were a superposition of the Eu2+ and Eu3+ emission and were independent of temperature from 18 K to ambient. To explain this effect the short distance compensation of the Eu3+ replacing Ca2+ in the β-Ca2SiO4 is discussed. It is argued that such compensation has to causes the conduction and valence bands bend. The existence of stable Eu2+ and Eu3+ replacing Ca2+ ion in lattice is discussed by consideration of the energies of the ground states of the Eu2+ and Eu3+, the Fermi energy and the energy necessary for creation of compensation defect

Enhanced photocatalytic activity of transparent carbon nanowall/TiO2 heterostructures

The synthesis of novel tunable carbon-based nanostructure represented a pivotal point to enhance the efficiency of existing photocatalysts and to extend their applicability to a wider number of sustainable processes. In this letter, we describe a transparent photocatalytic heterostructure by growing boron-doped carbon nanowalls (B-CNWs) on quartz, followed by a simple TiO2 sol-gel deposition. The effect on the thickness and boron-doping in the B-CNWs layer was studied, and the photocatalytic removal of nitrogen oxides (NOx) measured. Our results show that TiO2, in the anatase form, was uniformly deposited on the carbon nanowall layer. The underlying carbon nanowall layer played a double role in the heterostructure: it both affects the crystallinity of the TiO2 and promotes the separation of the photoexcited electron-holes, by increasing the number of contact points between the two layers. In summary, the combination of B-CNWs with TiO2 can enhance the separation of the electron–hole photogenerated charges, due to the peculiar CNWs maze-like structure

Luminescence Properties of LaAlO₃:Pr under Hydrostatic Pressure

The article presents the results of measuring the luminescence spectra, luminescence excitation spectra and luminescence spectra under high pressures for LaAlO3:Pr with concentration of 1%. The materials were synthesized by solid phase synthesis. Diffraction pattern is fully relates to LaAlO3 phase. The photoluminescence spectra show the main energy transitions. The change in the position of the main bands under the hydrostatic pressure of 23, 55, 160 and 191 kBar was demonstrated. The main band at 491 nm is slightly red-shifted, while the line at 605 nm is shifted to the high-energy part of the spectrum. The intensity of all bands increases with increasing hydrostatic pressure. The dynamics of changes in the intensities of maxima and emissions from different transitions are analyzed. Studies of luminescence under high hydrostatic compression are important in observing changes in the internal structure and electronic states of materials under the influence of high pressure, studying internal processes such as recombination of electrons and holes, transitions between energy levels and the release of photons. Understanding the changes that occur under compression can help researchers develop new materials with unique properties

Equation of state for Eu-doped SrSi2O2N2

alpha-SrSi2O2N2 is one of the recently studied oxonitridosilicates applicable in optoelectronics, in particular in white LEDs. Its elastic properties remain unknown. A survey of literature shows that, up to now, nine oxonitridosilicate materials have been identified. For most of these compounds, doped with rare earths and manganese, a luminescence has been reported at a wavelength characteristic for the given material; all together cover a broad spectral range. The present study focuses on the elastic properties of one of these oxonitridosilicates, the Eu-doped triclinic alpha-SrSi2O2N2. High-pressure powder diffraction experiments are used in order to experimentally determine, for the first time, the equation of state of this compound. The in situ experiment was performed for pressures ranging up to 9.65 GPa, for Eu-doped alpha-SrSi2O2N2 sample mounted in a diamond anvil cell ascertaining the hydrostatic compression conditions. The obtained experimental variation of volume of the triclinic unit cell of alpha-SrSi2O2N2:Eu with rising pressure served for determination of the Birch-Murnaghan equation of state. The determined above quoted bulk modulus is 103(5) GPa, its first derivative is 4.5(1.1). The above quoted bulk modulus value is found to be comparable to that of earlier reported oxynitrides of different composition. (C) 2014 AIP Publishing LLC