7790-75-2Relevant articles and documents
Synthesis of Tungstate Thin Films and Their Optical Properties
Saito, Nobuhiro,Kudo, Akihiko,Sakata, Tadayoshi
, p. 1241 - 1245 (1996)
A simple and new synthetic method of tungstate thin films (CaWO4, MgWO4, PbWO4, ZnWO4) was developed. The absorption and luminescence spectra of tungstate thin films synthesized on quartz substrates were measured; the optical properties were also studied. It was found that CaWO4 has Eg = 5.4 eV of a direct transition nature. Tungstate thin films were strongly luminescent when irradiated with UV-light. Excitation at around 290 nm was interpreted as a singlet-triplet transition.
Study of cationic substitution in Bi2WO6 and derived structures in the framework of the modular approach
Charkin,Kazakov,Lebedev
, p. 1248 - 1256 (2010)
The possibilities of substitution of lead, alkaline and rare earth, antimony, and tellurium cations for bismuth ions in the structure of the Bi 2WO6 ferroelectric and compounds with more complicated derived structures have been studi
An efficient near infrared photocatalyst of Er3+/Tm3+/Yb3+tridoped (CaWO4at(TiO2/CaF2)) with multi-stage CaF2nanocrystal formation
Huang, Shouqiang,Lou, Ziyang,Shan, Aidang,Zhu, Nanwen,Feng, Kaili,Yuan, Haiping
, p. 16165 - 16174 (2014)
The formation process of CaF2is critical for the improvement of upconversion properties of the CaF2based upconversion photocatalysts, and for this purpose a near-infrared (NIR) photocatalyst of Er3+/Tm3+/Yb3+tridoped (CaWO4at(TiO2/CaF2)) (ETY-CTC) was synthesized. CaF2nanocrystals are converted from CaWO4precursors in a multi-stage process, and the remaining CaWO4microspheres are wrapped in CaF2and TiO2nanocrystals to form the heterostructure of the photocatalyst. CaF2is found to connect with TiO2nanocrystals, instead of being coated by TiO2, resulting in a higher upconversion luminescence efficiency of ETY-CTC than that of pure Er3+/Tm3+/Yb3+tridoped (CaWO4@CaF2). ETY-CTC possesses higher photocatalytic activities compared to Er3+/Tm3+/Yb3+tridoped (CaWO4@TiO2) under NIR and UV-vis-NIR light irradiations, since more OH and O2-radicals, and higher electron-hole separation efficiency are obtained in the ETY-CTC system. The multi-stage formation of luminescence agents can be an attractive method for the synthesis of NIR photocatalysts with enhanced upconversion properties and photocatalytic activities. This journal is
Effects of slight structural distortion on the luminescence performance in (Ca1-xEux)WO4 luminescent materials
Wu, Feng-Nian,Yu, Hua-Jian,Hu, Yan-Yan,Zhang, Hua-Di,Zhang, Rui,Li, Jing,Liu, Bing,Wang, Xu-Ping,Yang, Yu-Guo,Wei, Lei
, p. 237 - 246 (2021)
(Ca1-xEux)WO4 (x = 0–21 mol%) phosphors were prepared using the classical solid-state reaction method. The influence of Eu3+ ion doping on lattice structure was observed using powder X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO4 lattice with a scheelite structure in the form of a Eu3+ ion, which introduced a slight lattice distortion into the CaWO4 matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f–f excitation transitions of Eu3+ activators. When the Eu3+ concentration was increased to 21 mol%, a local luminescence centre of [WO4]2? groups was detected in the matrix and manifested as the decay curves of [WO4]2? groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu3+ between different energy levels (such as 7F0→5L6, 7F0→5D2) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO4]2?→Eu3+ was efficient and incomplete.
Effect of noble metal element on microstructure and NO2 sensing properties of WO3 nanoplates prepared from a low-grade scheelite concentrate
Li, Tingting,Shen, Yanbai,Zhong, Xiangxi,Zhao, Sikai,Li, Guodong,Cui, Baoyu,Wei, Dezhou,Wei, Kefeng
, (2020)
To break the limitation of raw materials for preparing functional WO3 nanomaterials, a low-grade scheelite concentrate was selected as the tungsten source, and WO3 nanoplates doped with Ag, Pd, Au and Pt were synthesized through three combined processes including NaOH leaching, chemical precipitation and acidification. The microstructure and NO2 sensing properties of pure and noble metal-doped WO3 nanoplates were investigated. The microstructure characterization demonstrated that all WO3 products were composed of interlaced and irregular nanoplates with the thickness of 10–30 nm, and the length and width of these nanoplates were in the range of several hundred nanometers. NO2 sensing properties indicated that WO3 nanoplates doped with noble metal nanoparticles exhibited obviously higher responses and shorter response times than pure WO3 nanoplates. Especially, noble metal-doped WO3 nanoplates exhibited distinct behaviors in terms of the enhancement of sensing properties. Pd-doped WO3 nanoplates exhibited highest response to NO2, and Ag-doped WO3 nanoplates exhibited fastest response speed. Additionally, Ag-, Pd- and Pt-doped WO3 nanoplates exhibited a relatively lower optimal operating temperature. The enhanced NO2 sensing performance can be ascribed to the large specific surface area of WO3 nanoplates, the catalytic activities of noble metal nanoparticles, and the varied work function energies together with the lower activation energies.
Electron Delocalization in Mixed-Valence Molybdenum Polyanions
Sanchez, C.,Livage, J.,Launay, J. P.,Fournier, M.,Jeannin, Y.
, p. 3194 - 3202 (1982)
Electron transfer in mixed-valence molybdenum polyanions has been studied by ESR and optical spectroscopy.Two series of compounds belonging to the Lindqvist (Mo6O19) and the Keggin (XMo12O40) structural types have been considered.The degree of valence trapping and ground-state delocalization have been measured by ESR at very low temperature (4 K).Optical activation energies have been deduced from the position of intervalence transfer absorption bands.Thermal activation energies have been measured from a detailed analysis of the ESR line width and line shape within the 4 - 200-K temperature range.Values of the transfer integral J between adjacent molybdenum sites have been estimated from a comparison between optical and thermal activation energies.Experiments show that all of the studied polyanions belong to class II of mixed-valence compounds.Thermally activated electron hopping appears to be much easier in the Keggin structure than in the Lindqvist structure.
Synthesis and characterization of Ag+ and Zn2+ co-doped CaWO4 nanoparticles by a fast and facile sonochemical method
Neto, N.F. Andrade,Dias,Tranquilin,Longo,Li,Bomio,Motta
, (2020)
In this work, Ag+ and Zn2+ co-doped CaWO4 nanoparticles were obtained by fast and facile sonochemical method. The nanoparticles were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), visible ultraviolet spectroscopy (UV–Vis) and photoluminescence property. The photocatalytic activity was studied against methylene blue (MB) dye under sunlight and CaWO4 powders were tested in 3 reuse cycles. The diffractograms indicate the non-formation of secondary phases and the Rietveld refinement estimated the crystallite sizes, being 27.38, 19.89, 18.70 and 16.39 nm for the pure, Ag, Zn and Ag:Zn samples, respectively. SEM and TEM images showed that the particles are agglomerated and have a mean diameter ranging from 16.76 (Ag:Zn) to 71.76 nm (pure). Defects generated by doping shift the gap band to higher energies and act to prevent electron/hole (e?/h+) pair recombination, reducing photoluminescence and favoring CaWO4 photocatalysis. Scavenger methodology indicated that h+ is the main mechanism acting in photocatalysis, and the reuse tests indicated that the silver-doped sample, even with the better initial response, loses efficiency over the course of the cycle, while the co-doped sample maintains efficiency, and is therefore indicated for reuse photocatalysis applications in methylene blue dye degradation.
Size-induced symmetric enhancement and its relevance to photoluminescence of scheelite CaWO4 nanocrystals
Li, Liping,Su, Yiguo,Li, Guangshe
, (2007)
This work explores size-induced lattice modification and its relevance to photoluminescence properties of scheelite nanostructures. Ca WO4 nanocrystals, a prototype scheelite compound, exhibited a lattice expansion and an increased symmetry of structural units with physical dimension reduction, which is in contradiction to the trend previously reported in bulk CaW O4 at high pressures or high temperatures. Lattice variations in CaW O4 nanocrystals are probably due to the negative pressures that originated from strong defect dipole interactions on surfaces. The increased structural symmetry along with surface citric modifications produced a significant enhancement in photoluminescence of CaW O4 nanocrystals, indicating a quantitatively structural control over the electronic properties.
Double Double to Double Perovskite Transformations in Quaternary Manganese Oxides
Ji, Kunlang,Alharbi, Khalid N.,Solana-Madruga, Elena,Moyo, Gessica T.,Ritter, Clemens,Attfield, J. Paul
, p. 22248 - 22252 (2021)
Control of cation ordering in ABX3 perovskites is important to structural, physical and chemical properties. Here we show that thermal transformations of AA′BB′O6 double double perovskites, where both A and B sites have 1:1 cation order, to (A0.5A′0.5)2BB′O6 double perovskites with fully disordered A/A′ cations can be achieved under pressure in CaMnMnWO6 and SmMnMnTaO6, enabling both polymorphs of each material to be recovered. This leads to a dramatic switch of magnetic properties from ferrimagnetic order in double double perovskite CaMnMnWO6 to spin glass behaviour in the highly frustrated double perovskite polymorph. Comparison of double double and double perovskite polymorphs of other materials will enable effects of cation order and disorder on other properties such as ferroelectricity and conductivity to be explored.
Screening and Characterization of Ternary Oxides for High-Temperature Carbon Capture
Gaultois, Michael W.,Dunstan, Matthew T.,Bateson, Adam W.,Chan, Martin S. C.,Grey, Clare P.
, p. 2535 - 2543 (2018)
Carbon capture and storage (CCS) is increasingly being accepted as a necessary component of any effort to mitigate the impact of anthropogenic climate change, as it is both a relatively mature and easily implemented technology. High-temperature CO2 absorption looping is a promising process that offers a much lower energy penalty than the current state of the art amine scrubbing techniques, but more effective materials are required for widespread implementation. This work describes the experimental characterization and CO2 absorption properties of several new ternary transition metal oxides predicted by high-throughput DFT screening. One material reported here, Li5SbO5, displays reversible CO2 sorption, and maintains ～72% of its theoretical capacity out to 25 cycles. The results in this work are used to discuss major influences on CO2 absorption capacity and rate, including the role of the crystal structure, the transition metal, the alkali or alkaline earth metal, and the competing roles of thermodynamics and kinetics. Notably, this work shows the extent and rate to which ternary metal oxides carbonate are driven primarily by the identity of the alkali or alkaline earth ion and the nature of the crystal structure, whereas the identity of the transition ion carries little influence in the systems studied here.
