M Zawawi Siti Murni, Yahya Rosiyah, Hassan Aziz, Mahmud H N M Ekramul, Daud Mohammad Noh
Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia.
Chem Cent J. 2013 May 1;7(1):80. doi: 10.1186/1752-153X-7-80.
Metal tungstates have attracted much attention due to their interesting structural and photoluminescence properties. Depending on the size of the bivalent cation present, the metal tungstates will adopt structures with different phases. In this work, three different phases of metal tungstates MWO4 (M= Ba, Ni and Bi) were synthesized via the sucrose templated method.
The powders of BaWO4 (tetragonal), NiWO4 (monoclinic) and Bi2WO6 (orthorhombic) formed after calcination temperatures of 750, 650 and 600°C for 4 h respectively are found to be crystalline and exist in their pure phase. Based on Scherrer estimation, their crystallite size are of nanosized. BET results showed NiWO4 has the highest surface area. BaWO4 exhibited less Raman vibrations than the NiWO4 because of the increased lattice symmetry but Bi2WO6 showed almost the same Raman vibrations as BaWO4. From the UV-vis spectra, the band gap transition of the metal tungstates are of the order of BaWO4 > Bi2WO6 > NiWO4. Broad blue-green emission peaks were detected in photoluminescence spectra and the results showed the great dependence on morphology, crystallinity and size of the metal tungstates.
Three different phases of metal tungstates of BaWO4 (scheelite), NiWO4 (wolframite) and Bi2WO6 (perovskite layer) in their pure phase were successfully prepared by the simple and economical sucrose-templated method. The highest surface area is exhibited by NiWO4 while largest band gap is shown by BaWO4. These materials showed promising optical properties.
金属钨酸盐因其有趣的结构和光致发光特性而备受关注。根据存在的二价阳离子的大小，金属钨酸盐会采用不同相的结构。在本工作中，通过蔗糖模板法合成了三种不同相的金属钨酸盐MWO4（M = Ba、Ni和Bi）。
分别在750、650和600°C煅烧4小时后形成的BaWO4（四方相）、NiWO4（单斜相）和Bi2WO6（正交相）粉末被发现是结晶的且以纯相存在。基于谢乐估计，它们的微晶尺寸为纳米级。BET结果表明NiWO4具有最高的表面积。由于晶格对称性增加，BaWO4的拉曼振动比NiWO4少，但Bi2WO6的拉曼振动与BaWO4几乎相同。从紫外-可见光谱来看，金属钨酸盐的带隙跃迁顺序为BaWO4 > Bi2WO6 > NiWO4。在光致发光光谱中检测到宽的蓝绿色发射峰，结果表明其对金属钨酸盐的形态、结晶度和尺寸有很大依赖性。
通过简单且经济的蔗糖模板法成功制备了纯相的三种不同相的金属钨酸盐BaWO4（白钨矿）、NiWO4（黑钨矿）和Bi2WO6（钙钛矿层）。NiWO4表现出最高的表面积，而BaWO4表现出最大的带隙。这些材料显示出有前景的光学性质。
