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A convenient microwave-assisted process has been applied to prepare Scheelite-type SrWO4 microcrystals. The phase structures and morphologies of the products obtained at different time have been characterized by X-ray diffraction, transmission electron microscopy, and field-emission scanning electron microscopy. The results show that SrWO4 with various morphologies including nanoparticles, nanorod, dumbbell, and sphere shapes were synthesized. A possible mechanism to illustrate the formation of the SrWO4 structures was discussed. The examination of photoluminescence (PL) property revealed that their PL emission properties of the as-prepared SrWO4 microcrystals can be dependent on the morphologies, degree of crystal, and sizes of SrWO4. [ABSTRACT FROM PUBLISHER]

SrMoO4 and SrWO4 nanocrystals have been synthesized using Sr(NO3)2 and Na2MeO4 (Me = Mo and W) in ethylene glycol by a microwave irradiation method at 50% of 180 W for 20 min. The product phases were detected using X-ray and selected area electron diffractions. They show the body-centered primitive tetragonal structure with the lattice parameters of a = b = 5.4007 Å and c = 12.0330 Å for SrMoO4, and a = b = 5.4274 Å and c = 11.9241 Å for SrWO4. X-ray diffraction patterns of the products, obtained by simulation using CaRIne version 3.1 program, are in accordance with those of the corresponding experiment and International Centre for Diffraction Data. A transmission electron microscope revealed the presence of nanocrystals composing the products, with their sizes in the ranges of 14–40 and 14–38 nm for SrMoO4 and SrWO4, respectively. Six different vibrations of ν1( Ag), ν3( Bg), ν3( Eg), ν4( Bg), ν2( Ag), and νf.r.( Ag) were detected using a Raman spectrometer, and the ν3( F2) antisymmetric stretching and ν4( F2) bending modes of [MeO4]2− tetrahedrons using a Fourier transform infrared spectrometer. Photoluminescence emissions of SrMoO4 and SrWO4, caused by the 1 T2 → 1 A1 transition of electrons, were detected at 410 and 418 nm, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Metal tungstates (MeWO4, Me=Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO3)2·2H2O and Na2WO4·2H2O in ethylene glycol by the 5h sonochemical process. The tungstate phases with scheelite structure were detected with X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their calculated lattice parameters are in accord with those of the JCPDS cards. Transmission electron microscopy (TEM) revealed the presence of nanoparticles composing the products. Their average sizes are 42.0±10.4, 18.5±5.1 and 13.1±3.3nm for Me=Ba, Sr and Ca, respectively. Interplanar spaces of the crystals were also characterized with high-resolution TEM (HRTEM). Their crystallographic planes are aligned in systematic array. Six different vibration wavenumbers were detected using Raman spectrometer and are specified as ν 1(Ag), ν 3(Bg), ν 3(Eg), ν 4(Bg), ν 2(Ag) and free rotation. Fourier transform infrared (FTIR) spectra provided the evidence of scheelite structure with W–O anti-symmetric stretching vibration of [WO4]2− tetrahedrons at 786–883cm−1. Photoluminescence emission of the products was detected over the range of 384–416nm. [Copyright &y& Elsevier]