Synthesis and luminescence properties of colloidal lanthanide doped YVO 4
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Synthesis and luminescence properties of colloidal lanthanide doped YVO4 Arnaud Huignard, Thierry Gacoin, Frédéric Chaput and Jean-Pierre Boilot Laboratoire de Physique de la Matière Condensée, UMR CNRS 7643, Ecole Polytechnique, 91128 Palaiseau, France Patrick Aschehoug and Bruno Viana Laboratoire de Chimie Appliquée de l’Etat Solide, UMR CNRS 7574, ENSCP, 75005 Paris, France ABSTRACT Aqueous colloidal solutions of well dispersed YVO4:Ln (Ln = Eu, Nd) nanoparticles are synthesized through precipitation reactions at room temperature. In the case of YVO4:Eu, a luminescence quantum yield of 15% is found, which is not as high as in the bulk due to the existence of residual crystalline defects and nonradiative relaxations from the hydroxylated surface. Appropriate hydrothermal annealing and deuteration of the surface allow to rise the yield up to 38%. Incorporation of the nanocrystals into a transparent silica matrix is achieved through preliminary coating of the particles with a functionnalized silicon alkoxide and further dispersion into a sol-gel precursor solution. Such sol-gel materials doped with YVO4:Nd nanocrystals are transparent and exhibit the typical emission at 1.06 µm of the Nd3+ ion. INTRODUCTION Intensive research on the luminescent properties of chalcogenide nanomaterials has been carried out during this last decade. It has led to the synthesis of core-shell nanostructures (CdSe / ZnS [1]) or doped nanoparticles (CdS:Mn [2]) with narrow size distributions and high luminescence quantum yields. Oxide materials, which are extensively used in most of the devices devoted to the production of light like lamps, lasers, TV phosphors or X ray detectors [3], have recently been studied at the nanometer scale [4], [5]. Promising applications are expected in the fields of biological labels [6] and integrated optical systems. The basic idea of this work is to explore the potentialities of lanthanide (Ln) doped yttrium orthovanadate (YVO4) nanoparticles synthesized through colloidal chemistry. The choice of this material is explained by the excellent phosphor (Ln = Eu) and laser (Ln = Nd) properties exhibited by bulk YVO4 as an host matrix. In this paper, we first expatiate upon the optical properties of colloidal Ln (Ln = Eu, Nd) doped YVO4 nanoparticles. In a second part, we report on the synthesis of composite materials in which the nanocrystals are dispersed in a transparent sol-gel matrix. This kind of elaboration has proved its efficiency in the case of CdS nanoparticles [7] and could be an interesting alternative route to the difficult growth of high quality YVO4:Nd monocrystals for laser applications. EXPERIMENTAL SECTION Synthesis of the aqueous colloidal solutions The basic principle of the colloidal synthesis of the particles relies on an aqueous precipitation reaction at room temperature from Y(NO3)3, Nd(NO3)3 or Eu(NO3)3, and NaVO3 at pH=12.5. The obtained precipitate is subsequently dialyzed, sonicated and further stabilized with sodium hexametaphosphate. More details concerning this synthesis may be fou
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