Structure and Photoluminescence Properties of Rare-Earth (Dy3+, Tb3+, Sm3+)-Doped BaWO4 Phosphors Synthesized via Co-Precipitation for Anti-Counterfeiting

Barium tungstate (BaWO4) powders with various sintering temperatures, and BaWO4:Dy3+ phosphor samples with concentrations of different rare-earth (RE) activator ions (Dy3+, Sm3+, Tb3+) were prepared through co-precipitation. The structural, morphological, and photoluminescent characteristics of barium tungstate phosphors depend on the concentration of RE ions. The crystallographic characteristics of the synthesized BaWO4 were analyzed using X-ray diffraction (XRD) patterns. The size and shape of the crystalline particles were estimated based on images measured with a field emission scanning electron microscope (FE-SEM). As the sintering temperature of the BaWO4 particles increased from 400 °C to 1000 °C, the size of the particles gradually increased and showed a tendency to clump together. In the sample doped with 7 mol % Dy3+ ions, the intensity of all emission bands reached their maximum. The emission spectra of the RE3+-doped BaWO4 powders by excitation at 325 nm were composed of yellow (Dy3+), red (Sm3+), and green (Tb3+) band at 572, 640, and 544 nm. This indicates that most of the RE3+ ions absorbed the position without reversal symmetry in the BaWO4 lattice. These results propose that strong emission intensity and tunable color for the phosphors can be accomplished by rare-earth doped host with an suitable quantity. In addition, the phosphor thin films, having high transparency from aqueous colloidal solutions, were deposited on banknotes, and it is considered whether it is suitable for anti-counterfeiting applications.

Transport and surface charge density of univalent ion of polyvinyl chloride-based barium tungstate ion-exchange composite membrane for industrial separation of waste water

In the present study, a polyvinyl chloride-based barium tungstate ion-exchange membrane was synthesized by sol–gel method. The structure of membrane was studied in terms of Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. X-ray diffraction analysis confirms crystalline form of the composite membrane without any other impurity. Scanning electron microscopy and Fourier transform infrared spectroscopy analysis show the uniform arrangement of particles in the membrane with crack-free surface structure and presence of different functional groups of the organic-inorganic materials. The electrochemical properties like surface charge density ( D), transport number and mobility ratio of the ion-exchange composite membrane were theoretically evaluated and compared with observed values using “Teorell, Meyers and Sievers” method. Transport number follows the order as KCl <NaCl < LiCl < NH4Cl, while the surface charge density showed reversed order. The results showed that the low concentration of electrolytes favors the high mobility of univalent cation in the present study. The above result proves the analytical utility of polyvinyl chloride-based barium tungstate ion-exchange membrane in environmental management.