Effects of slight structural distortion on the luminescence performance in (Ca1-x Eux )WO4 luminescent materials

(Ca_1-x Eu_x )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 ⁷ F₀ →⁵ L₆ , ⁷ F₀ →⁵ D₂ ) 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.

Unexpected formation of scheelite-structured Ca1-xCdxWO4 (0 ≤ x ≤ 1) continuous solid solutions with tunable photoluminescent and electronic properties

Design of a solid solution with tunable functionality is an attractive strategy toward realizing novel devices with multi-functionalities. In this work, a series of Ca_1-xCd_xWO₄ solid solutions in the entire range 0 ≤ x ≤ 1 with tetragonal scheelite structure have been successfully prepared for the first time. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopies indicated that all the nanocrystals have a tetragonal scheelite structure without wolframite phase. Structural refinement data revealed that the lattice volume decreased with the replacement of Ca²⁺ by Cd²⁺ ions. UV-Vis diffuse reflectance spectra indicated that optical band gap reduced with the replacement of Ca²⁺ by Cd²⁺ ions. Scanning electron microscopic (SEM) images showed that morphologies of the nanocrystals changed with the chemical compositions. The structure evolution of the solid solutions was further investigated by high-resolution transmission electron microscopy (HRTEM). Moreover, the influence of chemical compositions on the photoluminescent and electric performance has been performed and discussed. The reported synthetic approach and findings reported here are important to understand the structure and structure-property relation of scheelite-structured tungstate and molybdate compounds, which has potential applications in the design of other kinds of novel functional materials.

Ultrathin LiCoO2 Nanosheets: An Efficient Water-Oxidation Catalyst

Ultrathin cation-exchanged layered metal oxides are promising for many applications, while such substances are barely successfully synthesized to show several atomic layer thickness, owing to the strong electrostatic force between the adjacent layers. Herein, we took LiCoO₂, a prototype cation-exchanged layered metal oxide, as an example to study. By developing a simple synthetic route, we synthesized LiCoO₂ nanosheets with 5-6 cobalt oxide layers, which are the thinnest ever reported. Ultrathin nanosheets thus prepared showed a surprising coexistence of increased oxidation state of cobalt ions and oxygen vacancy, as demonstrated by magnetic susceptibility, X-ray photoelectron, electron paramagnetic resonance, and X-ray absorption fine spectra. This unique feature enables a higher electronic conduction and electrophilicity to the adsorbed oxygen than the bulk. Consequently ultrathin LiCoO₂ nanosheets provided a current density of 10 mA cm^-2 at a small overpotential of a mere 0.41 V and a small Tafel slope of ∼88 mV/decade, which is strikingly followed by an excellent cycle life. The findings reported in this work suggest that ultrathin cation-exchanged layered metal oxides could be a next generation of advanced catalysts for oxygen evolution reaction.

Ag@Ag8W4O16 nanoroasted rice beads with photocatalytic, antibacterial and anticancer activity

Increasing resistance of pathogens and cancer cell line towards antibiotics and anticancer agents has caused serious health problems in the past decades. Due to these problems in recent years, researchers have tried to combine nanotechnology with material science to have intrinsic antimicrobial and anticancer activity. The metals and metal oxides were investigated with respect to their antimicrobial and anticancer effects towards bacteria and cancer cell line. In the present work metal@metal tungstate (Ag@Ag8W4O16 nanoroasted rice beads) is investigated for antibacterial activity against Escherichia coli and Staphylococcus aureus using Mueller-Hinton broth and the anticancer activity against B16F10 cell line was studied. Silver decorated silver tungstate (Ag@Ag8W4O16) was synthesized by the microwave irradiation method using Cetyl Trimethyl Ammonium Bromide (CTAB). Ag@Ag8W4O16 was characterized by using various spectroscopic techniques. The phase and crystalline nature were analyzed by using XRD. The morphological analysis was carried out using Field Emission Scanning Electron Microscopy (FE-SEM), and High Resolution Transmission Electron Microscopy (HR-TEM). Further, Fourier Transform Infrared Spectroscopy (FT-IR) and Raman spectral analysis were carried out in order to ascertain the presence of functional groups in Ag@Ag8W4O16. The optical property was investigated using Diffuse Reflectance Ultraviolet-Visible Spectroscopy (DRS-UV-Vis) and the band gap was found to be 3.08eV. Surface area of the synthesized Ag@Ag8W4O16 wasanalyzed by BET analysis and Ag@Ag8W4O16 was utilized for the degradation of organic dyes methylene blue and rhodamine B. The morphology of the Ag@Ag8W4O16 resembles roasted rice beads with breath and length in nm range. The oxidation state of tungsten (W) and silver (Ag) was investigated using X-ray photoelectron spectroscopy (XPS).

New insights into fluorinated TiO2 (brookite, anatase and rutile) nanoparticles as efficient photocatalytic redox catalysts

In this paper, we develop a fluorination methodology and optimize various synthesis conditions. We also demonstrate that photocatalytic redox activity is affected by the synergistic effect between surface fluorination and phase structure.