YVO 4 : RE 3+ (RE = Eu, Sm, Dy, Er) nanophosphors: Facile hydrothermal synthesis, microstructure, and photoluminescence
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YVO4: 10%RE3+ (RE = Eu, Sm, Dy, Er) nanophosphors have been synthesized by a facile modified hydrothermal technology to obtain the high purity. The key procedure for this hydrothermal process is the adding order of precursors, in which excess sodium vanadate should be added in the solution of rare earth nitrates. The microstructure (crystal phase, morphology, particle size) of these phosphors are characterized by x-ray powder diffraction, scanning electron microscope, and transmission electron microscope, which indicates that there are some cube-like crystals with tetragonal zircon structure and the average particle size is approximately 40 nm. The luminescent behaviors for the four rare earth ion-activated YVO4 nanophosphors have been studied, and, for YVO4: 10%Eu3+ nanophosphors in particular, it is found that a different hydrothermal process influences the phase composition, microstructure, and photoluminescence. This result suggests that the hydrothermal synthesis process (by adding sodium vanadate to the solution of rare earth nitrates) is favorable for YVO4 nanophosphor to obtain pure phase, small particle size, long luminescent lifetime, and high luminescence quantum efficiency.
I. INTRODUCTION
Rare earth-activated phosphors have attracted great interest because of their apparent advantages in high color purity, wide spectral range, long lifetime range, high energy efficiency, and great stability.1–5 Yttrium vanadate (YVO4) has been proven to be a useful host for photoactive rare earth ions, and it is used to prepare all kinds of phosphors that emit a variety of colors because high luminescence quantum yields can be obtained for the f-f transitions.6–10 In the past, the main research was focused on the Eu3+-activated YVO4, because it is an important commercial red-emitting phosphor used in such fields as color television, the cathode ray tube, and the high-pressure mercury lamp. Bulk vanadates are generally prepared by high-temperature solid-state reactions, which can permit the structural characteristics of the powders to change easily.11–13 A wealth of research has been reported on the preparation of lanthanide vanadates through the wet chemical method, such as chemical coprecipitation,14–20 the Pechini sol–gel process method,21,22 etc., to obtain the precursors. The hydrothermal process, which occurs under autogenous pressure and at temperatures above the boiling point of water in the autoclave, has been used extensively for the preparation of various oxide materials.23,24 The most advantageous hydrothermal process for the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0381
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 10, Oct 2009 Downloaded: 19 Apr 2015
synthesis of luminescent materials is the relatively low temperature for reaction (100–300 C) without milling or calcinations that could effectively save energy. The reaction is controlled by dissolution and/or precipitation of reactants in an aqueous medium. Thus, the particle si
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