VO4 Groups Research Articles

K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles.

ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn23+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = 10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at TN = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat Cp and Fisher's specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below TN. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.

Multi-Prismatic Hollow Cube CeVO4 with Adjustable Wall Thickness Directed towards Photocatalytic CO2 Reduction to CO.

Ternary orthovanadate compounds have received increasing attention due to their broad light absorption and diverse crystal structure. However, their multi-assembled crystal morphologies are limited mainly due to their initially polyatomic VO4 groups. In this study, multi-prismatic hollow cubic CeVO4 microstructures were fabricated by a one-step solvothermal method without any organic agents. The increase in wall thickness is in accordance with the radial direction of the quadrangular prism. Moreover, the overdose of the V precursor is favorable for the formation of hollow micro-cubic CeVO4, and the wall thickness changes from 200 to 700 nm. Furthermore, these CeVO4 microstructures were applied to photocatalytic CO2 reduction with a maximum CO generation rate of up to 78.12 μmol g-1 h-1 under visible light irradiation, which was several times higher than that of the other samples. This superior photocatalytic activity might be attributed to its good crystallinity and unique exposed interior structure. This study provides guidelines for the multi-assembled structure fabrication of ternary compounds and expands upon the exploration of the spatial structure of multivariate compounds.

Structural and Electrochemical Properties of Li2O-V2O5-B2O3-Bi2O3 Glass and Glass-Ceramic Cathodes for Lithium-Ion Batteries.

In this study, 20Li2O-60V2O5-(20 - x)B2O3-xBi2O3 (x = 5, 7.5, 10 mol%) glass materials have been prepared by the melt-quenching method, and the structure and morphology of the glass materials have been characterized by XRD, FTIR, Raman, and FE-SEM. The results show that the disordered network of the glass is mainly composed of structural motifs, such as VO4, BO3, BiO3, and BiO6. The electrochemical properties of the glass cathode material have been investigated by the galvanostatic charge-discharge method and cyclic voltammetry, and the results show that with the increases of Bi2O3 molar content, the amount of the VO4 group increases, and the network structure of the glass becomes more stable. To further enhance the electrochemical properties, glass-ceramic materials have been obtained by heat treatment, and the effect of the heat treatment temperature on the structure and electrochemical properties of the glass has been studied. The results show that the initial discharge capacity of the glass-ceramic cathode obtained by heat treatment at 280 °C at a current density of 50 mA·g-1 is 333.4 mAh·g-1. In addition, after several cycles of charging and discharging at a high current density of 1000 mA·g-1 and then 10 cycles at 50 mA·g-1, its discharge capacity remains at approximately 300 mAh·g-1 with a capacity retention rate of approximately 90.0%. The results indicate that a proper heat treatment temperature is crucial to improving the electrochemical properties of glass materials. This study provides an approach for the development of new glass cathode materials for lithium-ion batteries.

The Crystal Structure and Crystal Chemistry of Mineral-like Cd5(VO4)2(OH)4, a Novel Isomorph of Arsenoclasite and Gatehouseite

The pentacadmium bis(vanadate(V)) tetrahydroxide Cd5(VO4)2(OH)4 was synthesized under hydrothermal conditions, and its crystal structure was determined with single-crystal X-ray diffraction. The investigated compound is the second known compound next to Cd(VO3)2·4H2O synthesized in the CdO–V2O5–H2O system and crystallizes isotypically to the minerals gatehouseite, Mn5(PO4)2(OH)4, and its As analog arsenoclasite, Mn5(AsO4)2(OH)4. Its symmetry is orthorhombic, with a space group of P212121 and unit cell parameters of a = 19.011(4), b = 6.0133(12), c = 9.5411(19) Å, V = 1090.7(4) Å3, and Z = 4. The structure consists of double ribbons of M(O,OH)6-octahedra (M = Cd2, Cd3, Cd4) extending along [010] interconnected by edge- and corner-shared M(O,OH)6-octahedra (M = Cd1, Cd5) and discrete, slightly distorted VO4 tetrahedra, which form double chains of coupled polyhedra [V1O4–Cd5O4(OH)2–Cd1O5(OH)–V2O4]n running along the same direction. The interesting feature is the existence of V–Cd distances (3.0934(7) and 3.1081(7) Å for V1–Cd5 and V2–Cd1, respectively), which are shorter than the sum of the van der Waals radii of 3.71 Å. The V1–V2 distances of 4.1214(9) Å are also shorter than the sum of the van der Waals radii of 4.26 Å. The O–H···O hydrogen bonds additionally link the two subunits, ribbons, and chains into a three-dimensional structure. Raman spectra confirmed the presence of the hydrogen bonds and mutually isolated VO4 groups.

Rare-Earth Doped GdVO<sub>4</sub> by Sol-Gel Method: Structural and Luminescence Properties

Rare earths have been extensively developed in recent years, however, new hosts allow high excitation and emission efficiency, in this sense, gadolinium vanadate has been extensively studied and in previous works it has been widely used in down conversion systems. Because of the strong absorption of the VO4 groups and efficient energy transfer from GdVO4 to lanthanide ions, in this work its up-conversion properties were studied when is co-doped with Yb3+, X3+ where X = Tm, Er and Ho. The powders synthesized presented a high crystallinity and a rounded morphology and exhibit a high luminescence when are excited with IR radiation.

Kainotropite, Cu4Fe3+O2(V2O7)(VO4), a new mineral with a complex vanadate anion from fumarolic exhalations of the Tolbachik volcano, Kamchatka, Russia

ABSTRACT The new mineral kainotropite Cu4Fe3+O2(V2O7)(VO4) was found in sublimates of fumaroles related to the Tolbachik volcano, Kamchatka, Russia. The holotype specimen originates from the Yadovitaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption; associated minerals are hematite, langbeinite, calciolangbeinite, tenorite, piypite, lyonsite, rutile, pseudobrookite, sanidine, and lammerite. In paleo-fumarolic deposits of Mountain 1004 kainotropite is associated with diopside and hematite. It forms prismatic crystals up to 0.2 × 0.2 × 0.5 mm3, isolated or combined in clusters up to 0.7 mm across. Kainotropite is iron-black to reddish-black, with semi-metallic luster. Dcalc is 4.10 g/cm3. In reflected light, kainotropite is grey, weakly anisotropic. The reflectance values [Rmax–Rmin,% (λ, nm)] are: 18.3–17.3 (470), 17.3–16.3 (546), 16.9–15.7 (589), 16.3–15.1 (650). The chemical composition of the holotype sample (wt.%, electron microprobe) is: CuO 46.69, Al2O3 1.40, Fe2O3 10.04, TiO2 0.32, V2O5 37.58, As2O5 2.55, MoO3 0.76, total 99.34. The empirical formula, based on 13 O apfu, is: Cu3.96Fe3+0.85Al0.19Ti0.03(V2.78As0.15Mo0.04)Σ2.97O13. Kainotropite is orthorhombic, Pnma, a = 14.139(2), b = 6.7102(7), c = 11.4177(15) Å, V = 1083.3(2) Å3, and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 8.89(100)(101), 5.728(33)(002), 3.698(35)(212), 3.357(52)(020,203), 3.034(77)(220), 2.968(60)(303), and 2.655(27)(321,204). The crystal structure was solved from single-crystal XRD data, R = 0.085. Kainotropite represents a novel structure type. Cu2+ polyhedra (distorted tetragonal pyramids and strongly distorted octahedra) and Fe3+ octahedra are connected via common edges to form zigzag ribbons. Adjacent ribbons are connected by both V2O7 and VO4 groups (isolated from each other) to form a heteropolyhedral pseudo-framework. The name kainotropite is derived from the Greek word καινóτρoπoς, unusual, in allusion to its uncommon (for natural vanadates) anionic composition: it is the first mineral containing both pyrovanadate (V2O7)4– and orthovanadate (VO4)3– anions.

Influence of vanadium addition on the optical and photoluminescence properties of borate glasses and their glass–ceramic derivatives

Nominal B2O3–Na2O–CaO–SrO glasses containing various concentrations of V2O5 ranging from 5 to 40 mol% have been prepared by normal melting and quenching procedure. Data obtained from differential scanning calorimetry (DSC) of the parent glasses were used to prepare glass–ceramic. X-ray diffraction (XRD) patterns of glasses reveal an absence of any identified crystalline phases; while, patterns of the heat-treated glasses showed the crystallization of calcium vanadate (Ca3V2O8), sodium borate (Na2B6O10) and sodium vanadate (NaV3O8) phases. UV–Visible spectra demonstrated characteristic absorption in the UV region centered at ~ 234 and 360 nm that extended to the visible region with increasing V2O5 content. Consequently, the estimated optical parameters such as optical band gap (Eopt), Urbach energy (∆E) and refractive index were dependent on V2O5 content. Photoluminescence spectra were measured before and after crystallization indicating development in the emission spectra after heat treatment. The glasses reveal two sharp emitted peaks at about 466 and 552 nm while the glass–ceramic derivatives depicted an extended emission peak centered at about 700 nm. Based on FTIR data, tetrahedral and trigonal borate groups were identified beside VO4 group when V2O5 was added to the parent glasses. Infrared structural measurements reveal the dual role of V2O5 as glass modifier or former depending on its concentration.

Unconventional spin-glass-like state in AgCo2V3O10, the novel magnetically frustrated material

Single crystals of a new silver and-cobalt based vanadate AgCo2V3O10 were grown from a melted mixture. The crystal structure determination reveals that this new vanadate crystallizes in triclinic system with space group P-1. The structure of the titled compound is constructed from CoO6octahedra and VO4 tetrahedra sharing edges and vertices leading to an open three-dimensional framework delimiting tunnels along [001], where the Ag cations are located. The bands observed in Raman spectrum were assigned to corresponding vibrations of the VO4 groups. DC and AC magnetization (susceptibility) measurements revealed the spin-glass (SG) -type transition below a frequency-independent temperature Tf(H) that is nearly independent on the applied magnetic field. Magnetic field H> 10 kOe induces the spin glass antiferromagnet. These observations brings AgCo2V3O10 into the class of geometrically frustrated magnetic systems.

Color tunable photoluminescence properties in Eu3+ doped calcium bismuth vanadate phosphors for luminescent devices

Abstract Single phase Eu3+ activated calcium bismuth vanadate (CaBiVO5) phosphors have been successfully synthesized using solid state reaction method. X-ray diffraction (XRD) analysis confirms the pure phase formation and scanning electron microscope (SEM) micrographs exhibit inhomogeneous particle formation with irregular morphology of Eu3+ doped CaBiVO5 (CBV) phosphor. The photoluminescence excitation (PLE) spectrum indicates significant absorption in the ultraviolet (UV) and near ultraviolet (n-UV) spectral region for un-doped CBV sample, whereas Eu3+ doped CBV phosphors reveal various sharp absorption bands in n-UV and blue region along with host absorption bands. Trivalent europium activated CBV phosphors under 342 nm excitation exhibit dominant red emission peak at 613 nm wavelength accompanied by weak broadband originating from VO4 groups, whereas the phosphors under 464 nm excitation, exhibit similar emission profile with most intense one centered at 613 nm by excluding host emission bands. The energy transfer mechanisms and the probable cause for concentration quenching beyond 4.0 mol% of Eu3+ ions concentration have been discussed in detail. The CIE chromaticity coordinates for the optimized phosphor, (0.551, 0.398) and (0.639, 0.358), situated in the reddish-orange and red region under 342 and 464 nm excitations, respectively. The CIE coordinates calculated based on the emission spectra measured under 464 nm excitation are close to the commercial phosphor Y2O2S: Eu3+ (x = 0.622 and y = 0.351). All the above mentioned results support the utilization of Eu3+ doped CBV phosphor as a potential red emitting component for luminescent devices.

Undulated oxo-centered layers in PbLn3O4(VO4) (Ln= La and Nd) and relationship with Nd4O4(GeO4)

Single crystals of PbLa3O4(VO4) have been synthesized using the flux growth technique and characterized by X-ray diffraction. The crystal structure of the tittle phase was solved by charge flipping and refined to R1 = 0.024 (wR2 = 0.031) for 2777 reflections [I>3σ(I)]. The compound is orthorhombic and crystallized in the space group Cmcm: a = 5.8686(6)Å, b = 17.898(2)Å, c = 7.9190(7)Å, V = 831.8(1)Å3, Z = 4. The structure is built on [PbLa3O4]3+ layers with zig-zag cross-sections, surrounded by isolated (VO4)3- tetrahedra. Its crystal structure shows direct relationship with the isoformular Nd4O4(GeO4) compound which crystallized in the primitive non centrosymmetric Pb21m sub-group. Its stability in temperature and under air was checked as well as optical properties. In a second part, lanthanum was substituted by neodymium giving rise to a paramagnet and f→ f electronic excitations superposed to the broad absorption front below 3.05eV related to the presence of VO4 groups.

Effects of V2O5 on elastic, structural, and optical properties of mixed ionic–electronic 20Na2O–20CaO–(60 − x)B2O3–xV2O5 glasses

Glass samples [20Na2O–20CaO–(60 − x)B2O3–xV2O5, where 0 ≤ x ≤ 2.5 mol%] were prepared using melt-quenching method to study the mixed ionic–electronic (MIE) effect on the elastic and optical properties of the glasses. Ultrasonic velocities, elastic moduli, hardness, and Debye temperature decreased to a minimum at x = 1.5 mol%. The initial decrease in the elastic moduli may have been caused by the increase in the number of non-bridging oxygen (NBO). In this process, V2O5 acted as a modifier at low vanadium concentration but changed to a network former at x > 1.5 mol%. The FTIR spectra showed the presence of VO4, VO5, BO3, and BO4 vibration groups, and this result confirmed that V2O5 played a dual role in the glass network. Considerable decrease in dc conductivity (x = 1.5 mol%) signified a blocking effect on the ionic current in the MIE glasses. Interestingly, the observed anomaly in the elastic moduli coincided with the dc conductivity minima, indicating possible influence of the MIE effect on the elastic anomaly. Quantitative analysis using ideal bulk compression and ring deformation models showed a decrease in Kbc/Ke at x > 1.5 mol% which implies that ring deformation was reduced in the region. Furthermore, the MIE effect also influenced the optical properties of the investigated glasses. The optical band gap (E opt) and refractive index exhibited minimum and maximum values, respectively, at x = 1.5 mol%. The increase in concentration of NBOs and the defect states elucidated the significant changes in the E opt of the glasses.

Fabrication of Bi3+/Ln3+:LuVO4 (Ln = Eu, Sm, Dy, Ho) nanophosphors and its color-tunable optical performance

The novel Bi3+/Ln3+:LuVO4 (Ln = Eu, Sm, Dy, Ho) nanocrystals are successfully fabricated by a facile and mixed hydrothermal method. With 10mol% Bi3+ doping into the LuVO4 nanocrystal, the Ln3+ excitation band could be diverted from 293nm to 346nm, attributing to the dominant of Bi3+ - V5+ metal–metal charge transfer instead of O2- to V5+ within VO4 group before doping. Under 346nm excitation, the as-prepared nanophosphors yield intense multicolor emissions. The emission color of Bi3+/Ln3+:LuVO4 nanophosphors can be tuned through adjusting the doping Ln3+ ions. They may find potential applications as white light-emitting diode materials in color display field.

A novel Eu3+‐ and self‐activated vanadate phosphor of Ca4La(VO4)3O with oxyvanadate apatite structure

AbstractPure and Eu3+‐activated Ca4La(VO4)3O phosphors were prepared via three‐step solid‐phase synthesis. The phase formation and structure were investigated by X‐ray diffraction (XRD) with Rietveld refinements. All the samples crystallized in an apatite‐type structure. The morphological properties were measured via by SEM and EDS measurements. Ca4La(VO4)3O is a new vanadate optical material with a direct band feature and a band energy of 3.1 eV. The undoped Ca4La(VO4)3O phosphor presents self‐activated yellow luminescence from 400 nm to 750 nm with a maximum wavelength of 525 nm originating from VO4 groups. Luminescence characteristics of Ca4La(VO4)3O indicate that the phosphor is not sufficient for practical applications. In Eu3+‐activated Ca4La(VO4)3O, there is an efficient energy transfer from VO4 to Eu3+ ions. The luminescence spectra, concentration quenching, decay curves, color chromaticity, and quantum efficiencies (QE) of Ca4La(VO4)3O:Eu3+ were investigated. The phosphor presents optimal Eu3+ doping concentration of about 20 mol%. The dominant red emission in Ca4La(VO4)3O:Eu3+ is 615 nm from electronic 5D0→7F2 dipole transitions. The quantum efficiency and the luminescence stability of the pure and Eu‐activated Ca4La(VO4)3O were reported. The luminescence was discussed on the structural characteristics.

Impedance spectroscopy study and phase transition in phospho-vanadium mixed oxide LiZnV0.5P0.5O4

An X-ray crystallographic study has allowed us to identify a powder of the type LiZnV0.5P0.5O4, which contains 50% of vanadium and 50% of phosphore, inside the binary system LiZnVO4–LiZnPO4. The structure is isotypic with the phenacite like LiZnP04. X-ray diffraction patterns are indexed according to the lattice parameters of the rhombohedral system and the R3 space group. IR spectra show the presence of VO4 and PO4 groups in the network of this material. The experimental results indicate that $$\sigma_{\text{AC}}$$ ( $$\omega$$ ) is proportional to $$\left( {\omega^{n} } \right)$$ . The activation energy found from the Arrhenius plot confirms that the conduction processing of the material is not due to simple hopping mechanism. The temperature dependence of frequency exponent n was investigated to understanding the conduction mechanism in LiZnV0.5P0.5O4. The non-overlapping small Polaron tunneling (NSPT) model can explain the temperature dependence of the frequency exponent. A phase transition at T = 623 K has been evidenced by Differential scanning calorimetry (DSC) and subsequently confirmed by the analysis of dielectric and electric properties.

Theoretical analysis for ultrasonic properties of vanadate-phosphate glasses over an extended range of composition: Part II

Makishima-Mackenzie's theory and Abd El-Moneim's semi-empirical formulas were used to predict the compositional dependence of ultrasonic properties in binary V2O5-P2O5 (45mol%≥V2O5≤85mol%) glasses at room temperature and at 8MHz frequency. Anomalous behavior between the calculated dissociation energy per unit volume of the glass and ultrasonic properties was discussed in terms of the basic structural units that constituting the glass network. Values of the dissociation energy per unit volume of the glass were calculated from the average single bond strengths proposed by Dimitrov and Komatsu for chemical bonds in the basic structural units of V2O5 and P2O5 oxides. The ring deformation model has also been used to estimate the mean atomic ring size of the glass network from data of bulk modulus and average first-order stretching force constant of V-O-P linkages. It has been found that, the average single bond strengths of PO bonds in PO4 groups and VO bonds in VO4 and VO5 groups play a dominant role in correcting the anomalous behavior between the calculated dissociation energy per unit volume of the glass and ultrasonic properties. Values of the theoretical elastic moduli, which have been calculated on the basis of Makishima-Mackenzie's theory, are in a very good agreement with the corresponding experimental ones. Moreover, Abd El-Moneim's semi-empirical formulas, which correlate ultrasonic attenuation coefficient with the corrected dissociation energy per unit volume, mean atomic ring size, oxygen density and packing density, appear to be valid for the investigated glass samples.

Spectroscopic Studies on Nano-Single Crystal BiVO4 Glass Ceramic as Dye Degradation for Wastewater Purification

Five bismuth vanadate glass samples and their corresponding glass-ceramics containing Bi2O3 ranging between 10-40 mol% were prepared by melting and controlled heat treatment, respectively. The prepared samples were investigated by XRD, FTIR, and TEM. Some specimens were also subjected to magnetization testing. The glass samples containing higher content of V2O5exhibited precipitation of BiVO4 phase as indicated by XRD. Controlled heat treatment of those samples led to the formation of nano-single crystals of BiVO4 glass-ceramic materials. With increasing Bi2O3 content, the crystallinity tendency is increases. For the glass-ceramic samples, FTIR spectra confirmed the transformation of the VO5 group into the VO4 group with increasing Bi2O3 percent. TEM images show agglomerated particles in the case of milled glass and rounded nano-crystals in the case of their glass-ceramic derivatives. The magnetic properties of the glass and its corresponding glass ceramic sample that contains 20 mol% Bi2O3 reveal obvious ferrimagnetism. Spectroscopic studies results of the prepared glasses and their glass ceramic derivatives as candidates for dye degradation for methyl green dye show that glass samples are inactive towards the adsorption of dye; while the behavior of glass ceramic samples towards dye degradation proceeds as follows: the maximum amount adsorbed increases in the order of 10 % < 15% < 20 % mol% Bi2O3 containing samples then decreases from 30 % to 40 % mol% Bi2O3.

Near-infrared downconversion through host sensitized energy transfer in Yb3+-doped Na2YMg2(VO4)3

Host sensitized near-infrared emitting phosphor Na2YMg2(VO4)3:Yb3+ was fabricated by a sol–gel method. Efficient broad emission is observed under ultraviolet excitation ranging from 240nm to −400nm and this luminescence originates from ligand–metal charge transfer of 2p of O2− to 3d of V5+. Under excitation of ultraviolet light in the broad absorption band, intense near-infrared emission of Yb3+ around 974nm is observed for Yb3+-doped Na2YMg2(VO4)3. Through study of photoluminescence spectra, fluorescence decay curves and concentration-dependent luminescence, mechanism of energy transfer from VO4 group to Yb3+ was proposed to rationalize the downconversion process. This phosphor with performance of ultra-violet to near-infrared downconversion could have potential application in improving efficiency of silicon-based solar cell.

Tunable photoluminescence and magnetic properties of Dy(3+) and Eu(3+) doped GdVO4 multifunctional phosphors.

A series of Dy(3+) or/and Eu(3+) doped GdVO4 phosphors were successfully prepared by a simple hydrothermal method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectrometry (EDS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). The results indicate that the as-prepared samples are pure tetragonal phase GdVO4, taking on nanoparticles with an average size of 45 nm. Under ultraviolet (UV) light excitation, the individual Dy(3+) or Eu(3+) ion activated GdVO4 phosphors exhibit excellent emission properties in their respective regions. The mechanism of energy transfer from the VO4(3-) group and the charge transfer band (CTB) to Dy(3+) and Eu(3+) ions is proposed. Color-tunable emissions in GdVO4:Dy(3+),Eu(3+) phosphors are realized through adopting different excitation wavelengths or adjusting the appropriate concentration of Dy(3+) and Eu(3+) when excited by a single excitation wavelength. In addition, the as-prepared samples show paramagnetic properties at room temperature. This kind of multifunctional color-tunable phosphor has great potential applications in the fields of photoelectronic devices and biomedical sciences.

Evidence of "new hot spots" from determining the nonlinear optical behavior of materials: mechanistic studies of the vanadium borate crystal, Na3VO2B6O11.

A novel mechanism for the nonlinear optical (NLO) effects of vanadium borate crystals, Na3VO2B6O11 (NVB), with distorted VO4 groups was investigated. A comprehensive analysis of the structure-property relationship was performed by combining the experimental measurements, the electronic structures calculations, the SHG-weighted electron density and the real-space atom-contribution analysis to yield the linear and nonlinear optical properties. The contribution of a (VO4)(3-) anionic group to the second harmonic generation (SHG) response was more pronounced than that of the (BO3)(3-) anionic group, which plays a virtual role in the SHG effects in NVB. The anionic (BO3)(3-) groups make dominant contributions to the birefringence, whereas the contribution of the V(5+) cations to these linear optical effects is negligible.

Visible light-induced degradation of methylene blue by photocatalyst of bismuth layered Bi7VO13 nanoparticles

A visible-light-driven photocatalyst of Bi7VO13 nanoparticles was prepared by the Pechini method. The nanoparticles were characterized with the measurements such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and UV–vis absorption spectrum. Bi7VO13 presents the indirect allowed electronic transition with narrow band gap energy of 2.13eV. The photocatalyst shows an excellent activity on the photo-degradation of methylene blue (MB) under visible-light irradiation. The photocatalysis was discussed on the base of the structure characteristics such as (Bi2O2)2+ layers connected by the isolated VO4 groups and the good conductivity. This vanadate could be a potential photocatalyst.