Structural and optical characterization of metal tungstates (MWO4; M=Ni, Ba, Bi) synthesized by a sucrose-templated method

Abstract

BackgroundMetal 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.ResultsThe 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.ConclusionThree 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.

Brief Review of the Effects of Pressure on Wolframite-Type Oxides

“…This is translated into an increase of Eg for MgWO4, ZnWO4, and CdWO4, and a decrease of Eg for MnWO4. The same behavior than in MnWO4 has been reported for triclinic wolframite-related CuWO4 [35] and can be predicted for CoWO4, FeWO4, and NiWO4.…”

Femtosecond-laser-irradiation-induced structural organization and crystallinity of Bi2WO6

“…It is possible to note the disappearance of the band centred at 597 nm after fs laser irradiation. This behaviour can be associated with the presence of oxygen atoms acting as electron acceptors, which avoid the recombination process 104 . Figure 7 displays the deconvolution of the PL emissions.…”

Effect of pH on visible-light-driven photocatalytic degradation of facile synthesized bismuth vanadate nanoparticles

“…The smaller crystallite size hires high PL intensity and this phenomenon was reported by Quintana -Melgoza et al [41] stated that electronic properties such as chemical or ions, atomic arrangement and physical dimension will enhance the optical response of the material. The low intensity of the PL curve at pH 10 was due to the lesser recombination process that was mainly due to the presence of oxygen atoms which act as an electron capturer [42] and also due to the separation of charges from the photogenerated electron-hole pairs. Hence this material has a good characteristic approach towards photocatalytic applications.…”