High temperature annealing of micrometric Zn2SiO4:Mn phosphor powders in fluidized bed

Micrometric Zn1.8Mn0.2SiO4 phosphor powders prepared by spray pyrolysis have been annealed between 900 and 1200°C under ambient air atmosphere to exalt their luminescence properties. Two original gas-solid fluidization processes have been tested in order to limit sintering phenomena, and the post-treated products have been compared with those annealed using a conventional process in crucible. The crystallinity, the size distribution, the outer morphology and the luminescence properties of powders before and after treatment have been analysed. Massive sintering phenomena occur in crucible from 1000°C, whereas the original granulometry and spherical morphology are preserved till 1100°C in fluidized bed. The luminescence efficiencies are comparable for the three processes and maximal after annealing at 1200°C. It has been established that residual ZnO and manganese ions at oxidation state higher than 2, still present after treatment at 1100°C, are detrimental to good luminescence efficiency. Both disappear from samples post-treated at 1200°C

Chemical Vapor Deposition of silicon nanodots on TiO2 submicronic powders in vibrated fluidized bed

Silicon nanodots have been deposited on TiO2 submicronic powders in a vibrated Fluidized Bed Chemical Vapor Deposition (FBCVD) reactor from silane SiH4. Deposition conditions involving very low deposition rates have been studied. After treatment, powders are under the form of micronic agglomerates. In the operating range tested, this agglomerates formation mainly depends on the fluidization conditions and not on the CVD parameters. The best results have been obtained for anatase TiO2 powders for which the conditions of fluidization have been the most optimized. For these anatase powders, agglomerates are porous. SEM and TEM imaging prove that silicon nanodots (8-10 nm in size) have been deposited on the surface of particles and that this deposition is uniform on the whole powders and conformal around each grain, even if not fully continuous. Raman spectroscopy shows that the TiO2 powders have been partially reduced into TiO2-x during deposition. The TiO2 stoichiometry can be recovered by annealing under air, and IR spectroscopy indicates that the deposited silicon nanodots have been at least partly oxidized into SiO2 after this annealing

Grafting luminescent metal-organic species into mesoporous MCM-41 silica from europium(III)tetramethylheptanedionate, Eu(thd)3

Mixed systems with Eu(III) β-diketonates as optically active guest species, and mesoporous silicas MCM-41 as a host matrix have been investigated. The grafting of europium(III) onto the inner walls of unmodified MCM-41 has been achieved starting from Eu(thd)3 (thd = 2,2,6,6- tetramethyl-3,5-heptanedionate), using two routes: wet impregnation (WI) at room temperature,and chemical vapour infiltration (CVI) at 185 °C. In received hybrids, denoted Eu(thd)x@MCM- 41, the same maximum yield [Eu]/[Si] = 8.2 at% on average has been achieved with either methods. The molar ratio x = [thd]/[Eu] is 0.6 on average for WI samples, and 1.5 for CVI samples. In the latter, higher contents in thd compensate lower contents in silanols with respect to the former. Rationalizing the possible bonds exchanged at the silica surface leads to a great diversity of possible co-ordination schemes according to the expression Σ[Si(OH)nx (O)xEu(thd)3-x] (where Σ means that surface species are considered). Chromophore neutral ligands phenanthroline (phen) or bipyridine (bipy) have been added to induce efficient Eu3+ luminescence under 270–280 nm excitation, via the antenna effect. For the most favourable case, (phen)yEu(thd)x@MCM-41, the emission intensity at 612 nm under excitation at 270 nm is 2/3 that for the genuine heteroleptic complex Eu(thd)3(phen). Moreover the hybrid material is stable up to 440 °C

Vers la synthèse et le post traitement de micro et nano poudres par CVD en lit fluidisé

Grâce à leurs propriétés exceptionnelles, les nanomatériaux offrent des perspectives d’applications chaque jour plus prometteuses, et la mise au point de procédés de synthèse et de post traitement performants constitue aujourd’hui un point clé pour leur utilisation industrielle. Au-delà des nanotubes de carbone, les nanostructures en silicium constituent une cible stratégique dans le domaine de la nanoélectronique. Des études récentes ont montré que le procédé de CVD (Chemical Vapor Deposition) catalytique constitue une voie efficace pour former des nanofils de silicium, en utilisant le silane SiH4 comme source de silicium et l’or comme catalyseur. De premiers résultats obtenus sur substrats plans à pression atmosphérique sont présentés ici. Une première analyse de l’influence des paramètres opératoires est proposée dans le but de corréler les conditions d’élaboration aux caractéristiques morphologiques et structurales de ces nanofils. A terme, il s’agira de transposer ces conditions de synthèse au procédé de CVD en lit fluidisé en vue de produire massivement ces nanomatériaux pour des applications notamment en catalyse hétérogène. D’autre part, des poudres microniques luminophores de silicate de zinc dopé au manganèse Zn2SiO4 :Mn2+ ont été traitées thermiquement sous air entre 900 et 1200°C en creuset et en lit fluidisé vibré. La cristallinité des poudres s’est révélée être équivalente pour les deux procédés ; elle augmente avec la température et elle est donc optimale à 1200°C, tout comme les propriétés de luminescence de ces particules. Mais un frittage massif des particules est survenu en creuset dès 1000°C, alors que le lit fluidisé vibré a permis de conserver la granulométrie originelle jusqu’à 1100°C. Un intérêt majeur existe donc pour post traiter ce type de particules en lit fluidisé vibré. Plus largement, l’étude résumée ici ouvre d’importantes perspectives pour étendre les travaux à des poudres de granulométrie encore plus fine, et aussi pour mettre au point d’autres post traitements par des gaz de poudres micro et submicroniques, en particulier par CVD. Des travaux sont d’ores et déjà lancés au LGC avec ces nouveaux objectifs

Novel contributions on luminescent apatite-based colloids intended for medical imaging

The setup of colloidal hybrid nanosystems based on biomimetic calcium phosphate apatites doped with europium ions has recently raised great interest in the pharmacological community, especially due to their bio-inspired character. This is especially relevant in relation with medical imaging for cancer diagnosis. Questions however remain in relation to a number of applicability aspects, some of which have been examined in this contribution. In a first part of this work, we explored further the luminescence properties of such colloidal nanoparticles. We pointed out, upon excitation of europium, the existence of some non-radiative de-excitation via the vibration of O-H oscillators located at the vicinity of the Eu3þ luminescent centers. The replacement of Eu3þ by Tb3þ ions, less prone to non-radiative de-excitation, was then tested in a preliminary way and can be seen as a promising alternative. In a second part of this work, we inspected the possibility to store these colloids in a dry state while retaining a re-suspension ability preserving the nanometer size of the initial nanoparticles, and we propose a functional protocol involving the addition of glucose prior to freeze-drying. We finally showed for the first time, based on titrations of intracellular Ca2þ and Eu3þ ions, that folic acid-functionalized biomimetic apatite nanoparticles were able to target cancer cells that overexpress folate receptors on their membrane, which we point out here in the case of T-47-D breast carcinoma cells, as opposed to ZR-75-1 cells that do not express folate receptors. This contribution thus opens new exciting perspectives in the field of targeted cancer diagnosis, thus confirming the promise of biomimetic apatites-based colloidal formulations

Luminescence Properties of Mesoporous Silica Nanoparticles Encapsulating Different Europium Complexes: Application for Biolabelling

In this work we have synthesized and characterized new hybrid nanoplatforms for luminescent biolabeling based on the concept of Eu3+ complexes encapsulation in mesoporous silica nanoparticles (≈100 nm). Eu complexes have been selected on the basis of their capability to be excited at 365 nm which is a currently available wavelength, on routine epifluorescence microscope. For Eu complexes encapsulation, two different routes have been used: the first route consists in grafting the transition metal complex into the silica wall surface. The second way deals with impregnation of the mesoporous silica NPs with the Eu complex. Using the second route, a silica shell coating is realized, to prevent any dye release, and the best result has been obtained using Eu-BHHCT complex. However, the best solution appears to be the grafting of Eu(TTA)3-Phen-Si to mesoporous silica NPs. For this hybrid, mSiO2-Eu(TTA)3(Phen-Si) full characterization of the nanoplatforms is also presented

Organosilylated complex [Eu(TTA)₃(Bpy-Si)]: a bifunctional moiety for the engeneering of luminescent silica-based nanoparticles for bioimaging

A new highly luminescent europium complex with the formula [Eu(TTA)₃(Bpy-Si)], where TTA stands for the thenoyltrifluoroacetone, (C₄H3S)COCH₂COCF₃, chelating ligand and Bpy-Si, Bpy-CH₂NH(CH₂)₃(OEt)₃, is an organosilyldipyridine ligand displaying a triethoxysilyl group as a grafting function has been synthesized and fully characterized. This bifunctional complex has been grafted onto the surface of dense silica nanoparticles (NPs) and on mesoporous silica microparticles as well. The covalent bonding of [Eu(TTA)₃(Bpy-Si)] inside uniform Stöber silica nanoparticles was also achieved. The general methodology proposed could be applied to any silica matrix, allowed high grafting ratios that overcome chelate release and the tendency to agglomerate. Luminescent silica-based nanoparticles SiO₂-[Eu(TTA)₃(Bpy-Si)], with a diameter of 28 ± 2 nm, were successfully tested as a luminescent labels for the imaging of Pseudomonas aeruginosa biofilms. They were also functionalized by a specific monoclonal antibody and subsequently employed for the selective imaging of Escherichia coli bacteria

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

Grafting luminescent metal-organic species into mesoporous MCM-41 silica from europium(III)tetramethylheptanedionate, Eu(thd)3

International audienceMixed systems with Eu(III) β-diketonates as optically active guest species, and mesoporous silicas MCM-41 as a host matrix have been investigated. The grafting of europium(III) onto the inner walls of unmodified MCM-41 has been achieved starting from Eu(thd)3 (thd = 2,2,6,6- tetramethyl-3,5-heptanedionate), using two routes: wet impregnation (WI) at room temperature,and chemical vapour infiltration (CVI) at 185 °C. In received hybrids, denoted Eu(thd)x@MCM- 41, the same maximum yield [Eu]/[Si] = 8.2 at% on average has been achieved with either methods. The molar ratio x = [thd]/[Eu] is 0.6 on average for WI samples, and 1.5 for CVI samples. In the latter, higher contents in thd compensate lower contents in silanols with respect to the former. Rationalizing the possible bonds exchanged at the silica surface leads to a great diversity of possible co-ordination schemes according to the expression Σ[Si(OH)nx (O)xEu(thd)3-x] (where Σ means that surface species are considered). Chromophore neutral ligands phenanthroline (phen) or bipyridine (bipy) have been added to induce efficient Eu3+ luminescence under 270–280 nm excitation, via the antenna effect. For the most favourable case, (phen)yEu(thd)x@MCM-41, the emission intensity at 612 nm under excitation at 270 nm is 2/3 that for the genuine heteroleptic complex Eu(thd)3(phen). Moreover the hybrid material is stable up to 440 °C