Active hybrid materials by nanoscale chemistry
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Active hybrid materials by nanoscale chemistry Jean-Pierre Boilot1, Sophie Besson1,2, Valerie Buissette1, Thierry Gacoin1, Arnaud Huignard1, Christian Ricolleau3 1 LPMC, UMR CNRS 7643, Ecole Polytechnique, 91128 Palaiseau France 2 LSVI CNRS/Saint-Gobain, UMR CNRS 125, 39 quai Lucien Lefranc, 93303 Aubervilliers France 3 LMCP, UMR CNRS 7590, Universités Paris 6 et 7, 4 place Jussieu, 75252 Paris France ABSTRACT We present different arrangments of hybrid nano-objects for optical applications : - Highly concentrated luminescent colloids (II-VI quantum dots, YVO4:Ln) are prepared and stabilized through the grafting of organic molecules at their surface. These nanocrystals can further be used for the synthesis of well defined nanomaterials. For instance, highly luminescent transparent films for integrated optics are obtained by using YVO4:Ln nanocrystal- silica composites. - 3D random networks of quantum dots are prepared by gelation of colloids. As in the silica system, the transparent percolating structure can be described as homogeneous assemblies of fractal clusters whose sizes are inferior to visible-range wavelength. - 3D ordered arrays of quantum dots are prepared by a confined growth of nanocrystals in mesoporous silica films. Using these templates, the 3D ordering of nanoparticles can be extended at a large scale on different substrates. These high density arrangments of nanocrystals are required in different applications such as nonlinear optics or semiconductor lasers. INTRODUCTION It is now well-known that the physical properties of solids can be modified when its size approaches the nanometer scale. A huge amount of work has been performed to understand the origin of these new properties : dielectric confinement for metals, quantum confinement for semiconductors and superparamagnetism for single domain magnetic particles [1]. Concerning the chemical approach of nanoparticles, an important question is how to tailor nanoparticles to move towards a desired application? The first part of this paper concerns the luminescent nanoparticles which could be proposed as fluorescent tags to investigate and solve biological problems. Compared with usual organic dyes, the objective is to find a new class of luminescent nanoparticles which are brighter, more stable against photobleaching and narrower in spectral width. Numerous works have already been performed on luminescent semiconductor quantum dots [2].The usual system consists in zinc sulfide capped cadmium selenide nanoparticles. After functionalization, these quantum dots are water soluble and present a luminescence quantum yield of 18%. The emission wavelength can be controlled by the size, in the 2 to 10 nanometer range, due to quantum confinement effects. Another way to obtain highly luminescent nanoparticles is the doping of quantum dots by transition ions. For instance, CdS:Mn [3] and ZnSe:Mn [4] nanocrystals exhibit orange luminescence corresponding to an internal transition of manganese ions. We present here the synthesis of lanthanide-doped yttrium vanadate
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