Synthesis and Characterizations of YVO₄:Eu Colloids

International audienceWe present a new process for the synthesis of colloidal europium-doped yttrium vanadate with a particle diameter of about 10 nm. Nanocrystals are produced by precipitation of citrate complexes of rare-earth salts with sodium orthovanadate. NMR and IR studies show that the interaction between citrate ligands and lanthanide ions limits the growth of particles and ensures the stability of the colloidal solutions through electrostatic and steric repulsions. The optimized process leads to stable and highly concentrated transparent colloidal solutions in water (up to 400 g‚L-1)

Seeded growth of ultrathin gold nanoshells using polymer additives and microwave radiation

Nanoshells made of a silica core and a gold shell possess an optical response that is sensitive to nanometer-scale variations in shell thickness. The exponential red shift of the plasmon resonance with decreasing shell thickness makes ultrathin nanoshells (less than 10 nm) particularly interesting for broad and tuneable ranges of optical properties. Nanoshells are generally synthesised by coating gold onto seed-covered silica particles, producing continuous shells with a lower limit of 15 nm, due to an inhomogeneous droplet formation on the silica surface during the seed regrowth. In this paper, we investigate the effects of three variations of the synthesis protocol to favour ultrathin nanoshells: seed density, polymer additives and microwave treatment. We first maximised gold seed density around the silica core, but surprisingly its effect is limited. However, we found that the addition of polyvinylpyrrolidone during the shell synthesis leads to higher homogeneity and a thinner shell and that a post-synthetic thermal treatment using microwaves can further smooth the particle surface. This study brings new insights into the synthesis of metallic nanoshells, pushing the limits of ultrathin shell synthesis.Advanced Materials by DesignInitiative d'excellence de l'Université de Bordeau

New luminescent rare earth activated oxynitridosilicates and oxynitridogermanates with the apatite structure

New luminescent oxynitrides based on the apatite structure doped with Eu2+ and Ce3+ have been prepared by ammonolysis of oxysilicate or oxygermanate precursors. The host compounds have the general formula La10−xSrx(Si/Ge)6O27−x/2−3y/2Ny. When doped with divalent europium or trivalent cerium they present blue, green, yellowish green or orange luminescence under UV/blue excitation. Remarkable long wavelength emissions centred beyond 500 nm are observed for the Ce3+ activated oxynitridosilicates and oxynitridogermanates, with compositions La8.9Ce0.1SrSi6N0.37O25.95, La8.9Ce0.1SrSi6N1.06O24.91 (λem = 545 nm) and La9.9Ce0.1Ge6N2.46O23.31 (λem = 590 nm). The treatment of precursor oxides with the required cationic ratios in NH3 gas was used as a convenient general method to prepare the oxynitride materials at moderate temperatures. This allowed decreasing the nitriding temperature from 1600-1400 °C to 1050-600 °C with respect to the method generally used for the synthesis of luminescent (oxy)nitride silicates, the solid state reaction between oxides, nitrides and carbonates under a N2 or N2-H2 flow

Silver nanoshells with optimized infrared optical response: synthesis for thin-shell formation, and optical/thermal properties after embedding in polymeric films

We describe a new approach to making ultrathin Ag nanoshells with a higher level of extinction in the infrared than in the visible. The combination of near-infrared active ultrathin nanoshells with their isotropic optical properties is of interest for energy-saving applications. For such applications, the morphology must be precisely controlled, since the optical response is sensitive to nanometer-scale variations. To achieve this precision, we use a multi-step, reproducible, colloidal chemical synthesis. It includes the reduction of Tollens' reactant onto Sn 2+-sensitized silica particles, followed by silver-nitrate reduction by formaldehyde and ammonia. The smooth shells are about 10 nm thick, on average, and have different morphologies: continuous, percolated, and patchy, depending on the quantity of the silver nitrate used. The shell-formation mechanism, studied by optical spectroscopy and high-resolution microscopy, seems to consist of two steps: the formation of very thin and flat patches, followed by their guided regrowth around the silica particle, which is favored by a high reaction rate. The optical and thermal properties of the core-shell particles, embedded in a transparent poly(vinylpyrrolidone) film on a glass substrate, were also investigated. We found that the Ag-nanoshell films can convert 30% of the power of incident near-infrared light into heat, making them very suitable in window glazing for radiative screening from solar light.Investments for the Future Programme IdEx Bordeaux-LAPHI

Functionalized fluorescent oxide nanoparticles: Artificial toxins for sodium channel targeting and imaging at the single-molecule level

International audienceLanthanide ion-doped oxide nanoparticles were functionalized for use as fluorescent biological labels. These nanoparticles are synthesized directly in water, which facilitates their functionalization, and are remarkably photostable without emission intermittency. Nanoparticles functiqnalized with guanidinium groups act as artificial toxins and specifically target sodium channels. They are individually detectable in live cardiac myocytes, revealing a heterogeneous distribution of sodium channels. Functionalized oxide nanoparticles appear to be a novel tool that is particularly attractive for long-term single-molecule tracking

Structure and electrochromism of two-dimensional octahedral molecular sieve h’-WO3

Thanks to their versatile redox behaviors, octahedral molecular sieves show promise in a range of electrochemical applications. Here the authors report a hexagonal polymorph of tungsten trioxide, an octahedral molecular sieve that exhibits fast proton (de)insertion for electrochromic devices