Search Results (8)

Gd³⁺ and Sm³⁺ co-activation, the effect of cation substitutions and the creation of cation vacancies in the scheelite-type framework are investigated as factors influencing luminescence properties. Ag_xGd_{((2−x)/3)−0.3−y}Sm_yEu³⁺_0.3☐_(1−2x)/3WO₄ (x = 0.50, 0.286, 0.20; y = 0.01, 0.02, 0.03, 0.3) scheelite-type phases (A_xGS_yE) have been synthesized by a solid-state method. A powder X-ray diffraction study of A_xGS_yE (x = 0.286, 0.2; y = 0.01, 0.02, 0.03) shows that the crystal structures have an incommensurately modulated character similar to other cation-deficient scheelite-related phases. Luminescence properties have been evaluated under near-ultraviolet (n–UV) light. The photoluminescence excitation spectra of A_xGS_yE demonstrate the strongest absorption at 395 nm, which matches well with commercially available UV-emitting GaN-based LED chips. Gd³⁺ and Sm³⁺ co-activation leads to a notable decreasing intensity of the charge transfer band in comparison with Gd³⁺ single-doped phases. The main absorption is the ⁷F₀ → ⁵L₆ transition of Eu³⁺ at 395 nm and the ⁶H_5/2 → ⁴F_7/2 transition of Sm³⁺ at 405 nm. The photoluminescence emission spectra of all the samples indicate intense red emission due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. The intensity of the ⁵D₀ → ⁷F₂ emission increases from ~2 times (x = 0.2, y = 0.01 and x = 0.286, y = 0.02) to ~4 times (x = 0.5, y = 0.01) in the Gd³⁺ and Sm³⁺ co-doped samples. The integral emission intensity of Ag_0.20Gd_0.29Sm_0.01Eu_0.30WO₄ in the red visible spectral range (the ⁵D₀ → ⁷F₂ transition) is higher by ~20% than that of the commercially used red phosphor of Gd₂O₂S:Eu³⁺. A thermal quenching study of the luminescence of the Eu³⁺ emission reveals the influence of the structure of compounds and the Sm³⁺ concentration on the temperature dependence and behavior of the synthesized crystals. Ag_0.286Gd_0.252Sm_0.02Eu_0.30WO₄ and Ag_0.20Gd_0.29Sm_0.01Eu_0.30WO₄, with the incommensurately modulated (3 + 1)D monoclinic structure, are very attractive as near-UV converting phosphors applied as red-emitting phosphors for LEDs. Full article

Clinobisvanite (monoclinic scheelite BiVO₄, S.G.I2/b) has garnered interest as a wide-band semiconductor with photocatalyst activity, as a high NIR reflectance material for camouflage and cool pigments and as a photoanode for PEC application from seawater. BiVO₄ exists in four polymorphs: orthorhombic, zircon-tetragonal, monoclinic, and scheelite-tetragonal structures. In these crystal structures, V is coordinated by four O atoms in tetrahedral coordination and each Bi is coordinated to eight O atoms from eight different VO₄ tetrahedral units. The synthesis and characterization of doped bismuth vanadate with Ca and Cr are studied using gel methods (coprecipitated and citrate metal–organic gels), which are compared with the ceramic route by means of the UV–vis–NIR spectroscopy of diffuse reflectance studies, band gap measurement, photocatalytic activity on Orange II and its relation with the chemical crystallography analyzed by the XRD, SEM-EDX and TEM-SAD techniques. The preparation of bismuth vanadate-based materials doped with calcium or chromium with various functionalities is addressed (a) as pigments for paints and for glazes in the chrome samples, with a color gradation from turquoise to black, depending on whether the synthesis is by the conventional ceramic route or by means of citrate gels, respectively; (b) with high NIR reflectance values that make them suitable as fresh pigments, to refresh the walls or roofs of buildings colored with them; and (c) with photocatalytic activity. Full article

Green nanotechnology plays an important role in designing environmentally-benign and sustainable synthesis techniques to provide safer products for human health and environments. In this context, the synthesis of bismuth vanadate (BiVO₄) nanoparticles (NPs) based on green chemistry principles with the advantages of eco-friendliness, cost-effectiveness, and simplicity has been explored by researchers. Despite the advantages of these synthesis techniques, crucial aspects regarding their repeatability and large-scale production still need to be comprehensively explored. BiVO₄ NPs have shown excellent potential in the pharmaceutical industry, cancer therapy, and photocatalysis. BiVO₄ particles with monoclinic scheelite structures have been widely investigated for their environmental applications owing to their fascinating optical and electrical properties as well as their high stability and unique crystal structure properties. These NPs with good photostability and resistance to photocorrosion can be considered as promising nanophotocatalysts for degradation of pollutants including organic dyes and pharmaceutical wastes. However, additional explorations should be moved toward the optimization of reaction/synthesis conditions and associated photocatalytic mechanisms. Herein, recent developments regarding the environmentally-benign fabrication of BiVO₄ NPs and their photocatalytic degradation of pollutants are deliberated, with a focus on challenges and future directions. Full article

Monoclinic scheelite bismuth vanadate (BVO) microballs were prepared by a facile hydrothermal method and subsequently modified with 2 wt% of noble metals (NM = Au, Ag, Cu, Pt and Pd) by a photodeposition route. All materials were characterized by diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The photocatalytic performance was investigated by degradation of tetracycline antibiotic under visible light irradiation. Moreover, photocurrent generation under UV/vis was also examined. It was found that BVO modification with all tested NMs resulted in a significant improvement in photocatalytic performance. The highest activity was obtained for Cu/BVO with mainly oxidized forms of copper. Based on scavenger tests (∙O₂⁻ and ∙OH as the main responsible species for TC degradation) and redox properties, it was proposed that the Z-scheme mechanism between copper oxides and BVO was responsible for enhanced photocatalytic activity. However, the co-participation of zero-valent forms of NMs should also be considered, either as electron scavengers, plasmonic sensitizers or conductors. Presented data reveal that porous microballs, highly attractive for practical applications due to micro-sized diameter and efficient light harvesting inside the structure, could be efficiently used for environmental and energy purposes under solar radiation. Full article

BiVO₄ films were fabricated by radio frequency (RF) sputtering from a single target. The deposited BiVO₄ films were found to be rich in Bi, and the reason for the Bi-richness was investigated. It was inferred from the Monte Carlo simulation that, during sputtering, the transfer process of target atoms through argon gas played a major role in this phenomenon. The transfer process resulted in an imbalanced ratio of Bi and V, arising from the difference in atom mass and interaction radius. The high RF power was found to be effective in adjusting the Bi/V ratio, influencing the sputtering yield. This type of preferential sputtering was maintained by the diffusion of target atoms from the bulk to the surface. BiVO₄ films with monoclinic scheelite crystal structures were obtained at high RF power values and found to exhibit photocatalytic performances beneficial for photoanodic applications. Full article

In this research work, we reported the synthesis of a spherical-shaped bismuth vanadate (BiVO₄) photocatalyst using a cost-effective, simple, chemical hydrothermal method and studied the effect of deposition temperatures on the structural, morphological, optical properties, etc. The XRD result confirmed the monoclinic scheelite phase of BiVO₄. An XPS study confirmed the occurrence of Bi, V, and O elements and also found that Bi and V exist in +3 and +5 oxidation states, respectively. SEM micrographs revealed the spherical-shaped morphology of the BiVO₄ photocatalyst. Optical investigation showed that the bandgap of the BiVO₄ photocatalyst varied between 2.25 and 2.32 eV. The as-synthesized BiVO₄ photocatalyst was used to study the photocatalytic degradation of crystal violet (CV) dye under visible light illumination. The photocatalytic degradation experiment showed that the degradation percentage of crystal violet dye using BiVO₄ reached 98.21% after 120 min. Mineralization of crystal violet dye was studied using a chemical oxygen demand analysis. Full article

In situ high-temperature Raman spectra of polycrystalline KBi(MoO₄)₂ were recorded from room temperature to 1073 K. Thermal stability of the monoclinic KBi(MoO₄)₂ was examined by temperature-dependent XRD. The monoclinic phase transformed into the scheelite tetragonal structure at 833 K, and then to the monoclinic phase at 773 K. Quantum chemistry ab initio calculation was performed to simulate the Raman spectra of the structure of KBi(MoO₄)₂ high-temperature melt. The experimental Raman band at 1023 K was deconvoluted into seven Gaussian peaks, and the calculated results were in good agreement with the experimental data. Therefore, the vibrational modes of Raman peaks of molten KBi(MoO₄)₂ were assigned. It was confirmed that the isolated structure of [Bi(MoO₄)₂]⁻ monomer, consisting of Mo⁶⁺ centers and Bi³⁺ sub-centers connected by edge-sharing, mainly exists in the melt of KBi(MoO₄)₂. Full article

In the present study, BiVO₄ sample was prepared under different pH 0.5–13 without capping agent. Different morphology characteristics were observed, such as sheet crystal structure, cross crystal structure and branching crystal structure. The mechanism of the formation of BiVO₄ nanostructure was discussed. Under acid condition, sheet crystal structure was obtained. The phenomenon could be attributed to polymerization of vanadate in the presence of H⁺. In the weak alkaline solution, across structure and branching type morphology was obtained. The photocatalytic efficiency for the samples ranked as pH 5 > pH 3 > pH 7 > pH 9 > pH 1 > pH 11 > pH 13 > blank, which is in good agreement with X-ray diffraction (XRD) result. E. coli envelop was damaged in the presence of BiVO₄ under visible light. The protrusion on envelop was diminished by BiVO₄. Attenuated Total Reflection Fourier transformed Infrared Spectroscopy (ATR-FTIR) results suggested the intensity was weakened for the amide, phosphoric, –COO⁻ group and C-H bond in lipopolysaccharides (LPS), peptidoglycan and periplasm molecules. Full article