Luminescence Property of ZnWO 4 :Sm Nanopowders Synthesized with Wet Chemical Methods
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INTRODUCTION
IN the past few years, the rare-earth-doped tungstates crystals as a type of phosphor were studied widely because of the high luminescence efficiency of tungstates crystals.[1–6] The Sm3+ (4f5) ion is one of the most interesting trivalence rare earth ions because the fluorescence properties emitting 4G5/2 level exhibits relatively high quantum efficiency. Several previous studies on spectroscopic properties of Sm3+ ions in different matrices have revealed that the fluorescence yield of this rare earth ion is dependent strongly on its environment inside the structure network.[7–11] The luminescence property of Sm-substituted ZnWO4 powders with fixed Sm3+ content of 1.0 at. pct synthesized by aqueous salt metathesis reaction and calcined at different temperatures has been studied previously.[12] Subsequent investigations of the fluorescence yield of the ZnWO4 tungstate nanocrystals with different levels of Sm-substitution become a necessary topic. The ZnWO4 nanocrystals have been prepared via various processes including coprecipitated process,[13] the hydrothermal method,[14–16] the molten salt method,[17] a standard ceramics route,[18] the polymerized complex method,[19] spray pyrolysis,[20] aqueous salt metathesis reaction,[21] etc. The aqueous salt metathesis reaction route ensures proper distribution of the various metals ions resulting in a stoichiometric product and smaller particle size compared with some other procedures. Moreover, the aqueous salt metathesis reaction route is a low-cost technique especially suitable for mass production of the pure and doped ZnWO4 nanopowders. H.Y. HE, Professor, is with the Key Laboratory of Auxiliary Chemistry & Technology for Chemical Industry, Ministry of Education, Shaanxi University of Science and Technology, 710021 Xi’an, P.R. China. Contact e-mail: [email protected] Manuscript submitted December 1, 2010. Article published online February 18, 2012. 662—VOLUME 43B, JUNE 2012
In this work, we reported (1) the synthesis of the ZnWO4:Sm powders with a series of Sm content by aqueous solution reaction followed by calcination and (2) the luminescence properties of the Sm-doped ZnWO4 powders with different Sm3+ substitution level. II.
EXPERIMENTAL PROCEDURE
The ZnWO4:Sm powders were synthesized by a method based on an approach used previously for the fabrication of tungstates (MWO4, M = Mn, Co, Ni, and Cu).[8] The ZnCl2 and SmCl3 at Sm3+ proportions of 0, 1.0, 2.0, 5.0, 7.5, and 10.0 at. pct were dissolved in distilled water in six glass beakers, and equimolecular Na2WO4 were dissolved in distilled water in other six beakers. All the solutions have molar concentrations of 0.05 M. The solutions containing Zn2+ + Sm3+ with various Sm3+ proportion and the solution containing WO4 were then mixed dropwisely with constant stirring. The white precipitations were fast formed. By filtering and washing repeatedly with distilled water, the precipitations were then dried at 373 K (100 C) for 4 hours and calcined at 973 K (700 C) for 2 hours in air atmosphere. The phase of the ZnWO4:S
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