Synthesis, growth process and photoluminescence properties of SrWO4 powders (original) (raw)
Related papers
Visible light emission from bulk and nano SrWO4: Possible role of defects in photoluminescence
Journal of Luminescence, 2017
Nanocrystalline (n-SWO) and microcrystalline (b-SWO) samples of SrWO 4 were prepared using polyol and solid state diffusion method, respectively and their crystallite sizes were estimated by powder X-ray diffraction employing Williamson-Hall method. Morphostructural characterization using transmission electron microscopy (TEM) revealed the increased thermal agglomeration and size enhancement in b-SWO particles relative to n-SWO. The photoluminescence emission in both the samples was broad in the range of 400 to 650 nm. The emission consisted mainly of a narrow peak in the blue region and a broader emission in green region. The fraction of emission in the green region was higher for nanocrystalline SrWO 4 than its microcrystalline counterpart. The higher intensity of green emission in nanocrystalline sample is attributed to the large concentration of the oxygen related vacancies.
Room-temperature photoluminescence in structurally disordered SrWO[sub 4]
Applied Physics Letters, 2006
Intense and broad visible photoluminescent ͑PL͒ band in structurally disordered SrWO 4 compounds was observed at room temperature. The polycrystalline scheelite strontium tungstate ͑SrWO 4 ͒ samples prepared by the polymeric precursor method at different temperatures of annealing were structurally characterized by x-ray diffraction and Fourier transform Raman spectroscopy measurements. Quantum-mechanical calculations showed that the local disorder in the cluster of the network modifiers Sr has a very important role in the charge transfer. The experimental and theoretical results are in good agreement, indicating that the generation of the intense visible PL band can be related to short-range order-disorder degree in the scheelite structure.
Room-temperature photoluminescence in structurally disordered SrWO4
Applied Physics Letters, 2006
Intense and broad visible photoluminescent ͑PL͒ band in structurally disordered SrWO 4 compounds was observed at room temperature. The polycrystalline scheelite strontium tungstate ͑SrWO 4 ͒ samples prepared by the polymeric precursor method at different temperatures of annealing were structurally characterized by x-ray diffraction and Fourier transform Raman spectroscopy measurements. Quantum-mechanical calculations showed that the local disorder in the cluster of the network modifiers Sr has a very important role in the charge transfer. The experimental and theoretical results are in good agreement, indicating that the generation of the intense visible PL band can be related to short-range order-disorder degree in the scheelite structure.
Advanced Powder Technology, 2013
This paper reports our initial research to obtain SrWO 4 microcrystals by the injection of ions into a hot aqueous solution and their photocatalytic (PC) properties. These microcrystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements and Fourier transform (FT)-Raman spectroscopy. The shape and average size of these SrWO 4 microcrystals were observed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In addition, we have investigated the PC activity of microcrystals for the degradation of rhodamine B (RhB) and rhodamine 6G (Rh6G) dyes. XRD patterns, Rietveld refinement data and FT-Raman spectroscopy confirmed that SrWO 4 microcrystals have a scheelite-type tetragonal structure without deleterious phases. FT-Raman spectra exhibited 12 Raman-active modes in a range from 50 to 1000 cm À1 . FE-SEM and TEM images suggested that the SrWO 4 microcrystals (rice-like -95%; star-, flower-, and urchin-like -5%) were formed by means of primary/secondary nucleation events and self-assembly processes. Based on these FE-SEM/TEM images, a crystal growth mechanism was proposed and discussed in details in this work. Finally, a good PC activity was first discovered of the SrWO 4 microcrystals for the degradation of RhB after 80 min and Rh6G after 50 min dyes under ultraviolet-light, respectively. Advanced Powder Technology j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a p t rapidly injected into a hot aqueous solution (90°C), instantly forming a suspension. Afterwards, the SrWO 4 crystals precipitated at the bottom of the glass flask. Chemically, the SrWO 4 microcrystals are obtained by a fast reaction between (Sr 2+ :WO 2À 4 ) ions, as shown in the following Eqs. (1)-(3):
Chemical Physics, 2005
The nature of intense visible photoluminescence at room temperature of SrWO 4 (SWO) non-crystalline thin films is discussed in the light of experimental results and theoretical calculations. The SWO thin films were synthesized by the polymeric precursors method. Their structural properties have been obtained by X-ray diffraction data and the corresponding photoluminescence (PL) spectra have been measured. The UV-vis optical spectra measurements suggest the creation of localized states in the disordered structure. The photoluminescence measurements reveal that the PL changes with the degree of disorder in the SWO thin film. To understand the origin of visible PL at room temperature in disordered SWO, we performed quantum-mechanical calculations on crystalline and disordered SWO periodic models. Their electronic structures are analyzed in terms of DOS, band dispersion and charge densities. We used DFT method with the hybrid non-local B3LYP approximation. The polarization induced by the symmetry break and the existence of localized levels favors the creation of trapped holes and electrons, giving origin to the room temperature photoluminescence phenomenon in the SWO thin films.
This paper reports the synthesis of Eu-doped hydroxyapatite (HA:Eu) resulting in particles with nanorod diameters from 9 to 26 nm using the microwave hydrothermal method (HTMW). Eu 3+ ions were used as a marker in the HA network by basic hydrolysis followed by the HTMW treatment. The crystalline HA:Eu nanorod nature in a short-range order was detected by photoluminescence (PL) measurements from Eu 3+ emission into the HA matrix. Thus, was possible to verify that HA crystallization is favored in a short structural order when the HTMW treatment time was increased from 0 to 40 min and that the Eu 3+ substitution in the HA lattice is site-selective.
Microwave-assisted synthesis and characterization of SrMoO4 and SrWO4 nanocrystals
Journal of Nanoparticle Research, 2010
SrMoO 4 and SrWO 4 nanocrystals have been synthesized using Sr(NO 3) 2 and Na 2 MeO 4 (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 SrMoO 4 , and a = b = 5.4274 Å and c = 11.9241 Å for SrWO 4. 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 SrMoO 4 and SrWO 4 , respectively. Six different vibrations of m 1 (A g), m 3 (B g), m 3 (E g), m 4 (B g), m 2 (A g), and m f.r. (A g) were detected using a Raman spectrometer, and the m 3 (F 2) antisymmetric stretching and m 4 (F 2) bending modes of [MeO 4 ] 2tetrahedrons using a Fourier transform infrared spectrometer. Photoluminescence emissions of SrMoO 4 and SrWO 4 , caused by the 1 T 2 ? 1 A 1 transition of electrons, were detected at 410 and 418 nm, respectively.
Electronic structure, growth mechanism and photoluminescence of CaWO4 crystals
CrystEngComm, 2012
In this paper, aggregated CaWO 4 micro-and nanocrystals were synthesized by the co-precipitation method and processed under microwave-assisted hydrothermal/solvothermal conditions (160 C for 30 min). According to the X-ray patterns, all crystals exhibited only the scheelite-type tetragonal structure. The data obtained by the Rietveld refinements revealed that the oxygen atoms occupy different positions in the [WO 4 ] clusters, suggesting the presence of lattice distortions. The crystal shapes as well as its crystallographic orientations were identified by field-emission scanning electron microscopy and high-resolution transmission electron microcopy. Electronic structures of these crystals were evaluated by the first-principles quantum mechanical calculations based on the density functional theory in the B3LYP level. A good correlation was found between the experimental and theoretical Raman and infrared-active modes. A crystal growth mechanism was proposed to explain the morphological evolution. The ultraviolet-visible absorption spectra indicated the existence of intermediary energy levels within the band gap. The highest blue photoluminescence emission, lifetime and quantum yield were observed for the nanocrystals processed in the microwave-assisted solvothermal method.
Visible PL Phenomenon at Room Temperature in Disordered Structure of SrWO 4 Powder
Journal of Computer-aided Materials Design, 2005
The SrWO4 (SWO) powders were synthesized by the polymeric precursor method and annealed at different temperatures. The SWO structure was obtained by X-ray diffraction and the corresponding photoluminescence (PL) spectra was measured. The PL results reveal that the structural order–disorder degree in the SWO lattice influences in the PL emission intensity. Only the structurally order–disordered samples present broad and intense PL band in the visible range. To understand the origin of this phenomenon, we performed quantum-mechanical calculations with crystalline and order–disordered SWO periodic models. Their electronic structures were analyzed in terms of band structure. The appearance of localized levels in the band gap of the order–disordered structure was evidenced and is a favorable condition for the intense PL to occur.
Influence of chemical substitution on the photoluminescence of Sr(1−)Pb WO4 solid solution
Journal of Solid State Chemistry, 2015
The solid solution Sr 1 À x Pb x WO 4 based on luminescent tungstates SrWO 4 and PbWO 4 has been synthesized by solid-state reaction for all compositions 0r x r1. Using Rietveld method, the structural data of all polycrystalline samples have been refined and crystal cell parameters exhibited a linear behavior as a function of x. All substituted structures are of scheelite type. Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. Infrared and Raman spectroscopy have been performed to characterize the evolution of vibrational modes with substitution rate. Finally, a systematic study of luminescence under X-ray excitation has been performed: in the composition range x ¼0.2 to 0.4, intensities of emission exhibited increased values. The luminescence profiles have been interpreted in terms of four Gaussian components, two of them depending on substitution rate.