Study of small distorsions in Bi12MO20 oxides by simple exafs transmission technics

International audienceIn some Bi12 [A+xα B+yβ]O20 sillenite type phases the interatomic distances between oxygen and A or B cations located in tetrahedral sites of the lattice can be determined by EXAFS despite difficult recording conditions due to relatively low concentrations of A and B species in presence of strong absorbing bismuth

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 (+/-3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica nanoparticles (40 (+/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen

Hydrothermal Synthesis, Microstructure and Photoluminescence of Eu3+-Doped Mixed Rare Earth Nano-Orthophosphates

Eu3+-doped mixed rare earth orthophosphates (rare earth = La, Y, Gd) have been prepared by hydrothermal technology, whose crystal phase and microstructure both vary with the molar ratio of the mixed rare earth ions. For LaxY1–xPO4: Eu3+, the ion radius distinction between the La3+ and Y3+ is so large that only La0.9Y0.1PO4: Eu3+ shows the pure monoclinic phase. For LaxGd1–xPO4: Eu3+ system, with the increase in the La content, the crystal phase structure of the product changes from the hexagonal phase to the monoclinic phase and the microstructure of them changes from the nanorods to nanowires. Similarly, YxGd1–xPO4: Eu3+, Y0.1Gd0.9PO4: Eu3+ and Y0.5Gd0.5PO4: Eu3+ samples present the pure hexagonal phase and nanorods microstructure, while Y0.9Gd0.1PO4: Eu3+ exhibits the tetragonal phase and nanocubic micromorphology. The photoluminescence behaviors of Eu3+ in these hosts are strongly related to the nature of the host (composition, crystal phase and microstructure)

Functionalized Mesoporous SBA-15 with CeF3: Eu3+ Nanoparticle by Three Different Methods: Synthesis, Characterization, and Photoluminescence

Luminescence functionalization of the ordered mesoporous SBA-15 silica is realized by depositing a CeF3: Eu3+ phosphor layer on its surface (denoted as CeF3: Eu3+/SBA-15/IS, CeF3: Eu3+/SBA-15/SI and CeF3: Eu3+/SBA-15/SS) using three different methods, which are reaction in situ (I-S), solution impregnation (S-I) and solid phase grinding synthesis (S-S), respectively. The structure, morphology, porosity, and optical properties of the materials are well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, N2 adsorption, and photoluminescence spectra. These materials all have high surface area, uniformity in the mesostructure and crystallinity. As expected, the pore volume, surface area, and pore size of SBA-15 decrease in sequence after deposition of the CeF3: Eu3+ nanophosphors. Furthermore, the efficient energy transfer in mesoporous material mainly occurs between the Ce3+ and the central Eu3+ ion. They show the characteristic emission of Ce3+ 5d → 4f (200–320 nm) and Eu3+5D0 → 7FJ(J = 1–4, with 5D0 → 7F1 orange emission at 588 nm as the strongest one) transitions, respectively. In addition, for comparison, the mesoporous material CeF3: Eu3+/SBA-15/SS exhibits the characteristic emission of Eu3+ ion under UV irradiation with higher luminescence intensity than the other materials

ÉTUDE PAR MICROSCOPIE ÉLECTRONIQUE ET SPECTROSCOPIE OPTIQUE DU SYSTÈME ZrO2/Y2O3 : Eu

Les techniques conjuguées de la diffraction des rayons X, de la diffraction électronique et de la spectroscopie optique ont été appliquées à l'étude du système ZrO2/Y2O3. Dans l'intervalle 90 ZrO2/10 YO1,5—C-Y2O3 aucune phase ordonnée n'a été décelée par les techniques de diffraction. La spectroscopie optique révèle une tendance à l'ordre à courte distance ou peut-être seulement l'existence d'une coordination préférentielle des cations dictée par la composition.X-Ray diffraction, electronic diffraction and optical spectroscopy techniques have been applied to the study of the ZrO2/Y2O3 system. Diffraction techniques did not reveal any ordered compound in the range 90 ZrO2/10 YO1,5—C-Y2O3. By optical spectroscopy, one might suspect some very short range ordering or perhaps the existence of a preferred coordination polyhedron, for cations, assigned by composition

Luminescent Terbium Doped Aluminate Particles: Properties and Surface Modification with Asparagine

New luminescent organic-inorganic hybrid particles based on Tb-doped aluminates and asparagine (Asn) surface modifiers were investigated. The Tb 3+ doped inorganic core was obtained by spray pyrolysis, at 200 °C γ-AlOOH (BOE:Tbx%) or at 700 °C γ-Al 2 O 3 (γTA:Tbx%). The reaction of Asn with boehmite in water disaggregated the sub-micronic boehmite particles to give stable dispersion of surface modified nanoparticles Asn:BOE:Tbx% (x = 1 or 5). Concerning the Asn:γTA:Tbx% system, an Asn film wrapping alumina particles was observed. Photoluminescence spectra exhibited the bands assigned to Tb 3+ 5 D 4 → 7 F J = 6-3 transitions. A broad absorption band (240 nm) was assigned to the host (aluminate) to ion (Tb 3+ ) energy transfer. Efficient energy transfer was observed when active ions are incorporated in the defect-spinel structure of γTA, whereas it was relatively weak for BOE:Tb where Tb 3+ are bonded to the hydroxyls groups at nanocrystals surface. It is noticeable that Asn strengthens the linkage of Tb 3+ with the aluminate matrix, enhancing the host to dopant energy transfer

Étude par spectroscopie d’absorption X des verres de chalcogénures obtenus sous forme massive ou de couches minces par PECVD ou évaporation

Lors de l’étude des verres GeSey par EXAFS, le cristal GeSe2 a été choisi comme référence. Selon le degré de broyage GeSe2 (c) peut devenir vitreux formant ainsi des clusters conformément à l’hypothèse au cluster partiellement cristallisé de Phillips. Pour les verres GeSey massifs l’étude au seuil sélénium apporte la preuve d’un environnement mixte Ge-Se-Se et confirme le modèle de percolation rigide. Au seuil germanium, les verres massifs présentent une dépolymérisation faible (24,5 %) par rapport aux films minces (~ 40 %)

EVIDENCE FOR SHORT Cu(I)-Cu(I) DISTANCES IN COPPER-EXCESS SPINELS FROM EXAFS

L'étude EXAFS des spinelles Cu2x Cr2x Sn2-2x S4 a été réalisée dans le but de déterminer les caractéristiques structurales du cuivre monovalent spécialement pour les formulations surstoechiométriques en cuivre (2x >1). Nous avons montré que le cuivre se partage entre les sites tétraédriques 8a habituels et les sites octaédriques normalement vides où il occupe une position excentrée proche d'une face triangulaire. De plus, des distances courtes Cu-Cu (2,35 Å) sont mises en évidence, en accord avec l'arrangement relatif des sites.The Cu2x Cr2x Sn2-2x S4 spinel compounds have been investigated using EXAFS, especially as far as the structural features of monovalent copper excess are concerned, i.e. for 2x > 1. It has been shown that part of Cu is tetrahedrally surrounded (8a-sites) whereas the remaining part is triangularly coordinated in the vicinity of a face of the usually empty octahedral sites. In addition, the evidence for short Cu-Cu distances (2.35 Å) is given, in agreement with the octahedral- and tetrahedral- site arrangement