YVO4 Research Articles

Preparation of YVO4 powder from the Y2O3 + V2O5 + H2O system by a hydrolysed colloid reaction (HCR) technique

Prior to the formation of YVO4 in the Y2O3 + V2O5 + H2O system, two intermediate, partially hydrophobic, complex colloidal mixtures with metastable characteristics can be produced at room temperature and atmospheric pressure. The ball-milled system, having both hydrophobic and hydrophilic species, transforms into the stable yttrium orthovanadate phase due to intensive hydrolysis. At room temperature an orange mixture (possessing dispersed Y2O3 and 4Y2O3−P(OH) + ·2VO 3 − , Y2O3−p(OH) + ·6VO 3 − ·xH2O-like heteroaggregations) formed by 20 h mixing at pH ca. 4.0 transforms slowly, another red-brown heavily flocculated colloidal mixture (with dispersed Y2O3 and Y2O3−p(OH) + ·V10O 28 6− ·yH2O-like aggregation) formed by 70 h mixing at pH ca. 4.5 transforms rapidly into YVO4 in water. During additional mixing of highly diluted red-brown mixtures this transformation can be completed at room temperature. At elevated temperatures (50–95 °C) the orange mixture precipitates into a red-brown decavanadate-type precipitatium which subsequently can also rapidly hydrolyse into an orthovanadate phase in the diluted aqueous systems. Both vanadium excess meta-and decavanadate-type aggregations exhibit amorphous character by X-ray diffraction. The semi-hydrophobic colloidal structure can modify the dissociation mechanism, which prevents the system from returning to the starting oxides, and gives a new HCR technique for YVO4 preparation with a simple hydrolysis process at low temperatures and atmospheric pressure.

Flux growth of yttrium ortho-vanadate crystals

An yttrium ortho-vanadate (YVO 4) single crystal has been successfully grown from V 2O 5 and PbOV 2O 5 flux solutions. In the PbOV 2O 5 flux system, YVO 4 single crystals were grown at the bottom part of the crucible cooled by a heat exchanger, whereas in the V 2O 5 flux, single crystals were grown at the upper part of the crucible due to the evaporation of V 2O 5 during the growth process. Crystals up to 10 mm × 5 mm × 2 mm were grown from the V 2O 5 flux solutions. Nearly stoichiometric crystals with an atomic ratio, V Y , of 0.996 were found to be grown from the V 2O 5 flux, whereas compositions of the crystals grown from the PbOV 2O 5 flux, V Y = 0.976 , are close to the congruent composition, V Y = 0.972 .

Non-stoichiometry in yttrium ortho-vanadate

The existence of non-stoichiometric solid-solution phase in YVO 4 has been examined by the compositional variations in the lattice parameters and the photoluminescence intensities. The lattice parameters, c-axis, a-axis and c/a ratio, and the photoluminescence intensities ( λ=440 nm) vary apparently with the vanadium content of the sintered YVO 4 specimens. A vanadium deficient non-stoichiometric solid-solution ranging from about 48 to 50 mol% of vanadium content is suggested to be formed by the generation of vanadium vacancy.

Decoloration of yttrium orthovanadate laser host crystals by annealing

Decoloration of a Czochralski-grown YVO(4) laser host is studied by evaluation of the optical absorption and the photoluminescence spectrum before and after annealing under various atmospheres. Decoloration of yellow asgrown crystals, as a result of the decrease in the absorption near the absorption edge, occurs independently of the air, N(2), and O(2) annealing atmospheres. The most dramatic decrease in the absorption is seen in N(2). Annealing in N(2) atmosphere is suggested to be effective for obtaining the highly transparent crystals.

Synthesis and properties of iron, aluminium and yttrium vanadates

Synthesis and properties of iron, aluminium and yttrium vanadates

Growth studies of YVO4 crystals (II). Changes in YVO‐stoichiometry

AbstractIncongruent vanadium oxide vaporization of yttrium orthovanadate (YVO4) melt generates changes in both oxygen and yttrium‐vanadium (YV) stoichiometry. Slightly modified YVO4 or YVO4 + Y8V2O17 phases are formed from continuously changing melt systems depending on their starting compositions. The occurrence of Y8V2O17 in yttrium orthovanadate crystal fibers grown by laser heated pedestal growth (LHPC) technique can be simply eliminated by utilization of suitable V2O5‐excess starting compositions. In contrast, the oxygen‐deficient YVO4–x black phase is an inherently oxygen deficient phase with limited solid solution in the YVO4YVO3 subsystem of Y2O3V2O5V2O3 complex ternary phase diagram close to the congruent YVO4 composition (49.3 mol% V2O5–50.7 mol% Y2O3). The greater oxygen deficiency YVO4–x specimens have smaller lattice parameters as determined from detailed XRD data. Ceramic feed rod and fiber crystal grown from the feed rod with slight yttrium oxide excess starting composition were characterized by electron microprobe analysis. Changes in both YV and oxygen stoichiometry were observed along the fiber, due to double limited solid solution system of three dimensional ternary phase diagram. Consequently, both the presence of Y8V2O17 phase and change of YV stoichiometry over oxygen deficiency cause difficulties for YVO4 crystal growth from yttrium oxide excess melt.

Growth of oxygen deficiency-free YVO 4 single crystal by top-seeded solution growth technique

In spite of its excellent properties, yttrium orthovanadate (YVO 4) laser host single crystal has not been successfully adopted into high-tech applications because of crystal growth difficulties in connection with oxygen loss. This work is the first to apply a top-seeded solution growth (TSSG) technique to YVO 4, by which oxygen deficiency-free crystals can be directly grown. Since undesirable non-pentavalent vanadium oxides are continuously forming during the YVO 4, growth process, the flux media, in addition to the conventional TSSG requirements, must prevent the formation of oxygen deficient yttrium vanadate crystals. From these multiple requirements, lithium metavanadate (LiVO 3) was selected as the best solvent for YVO 4 flux growth. LiVO 3 has suitable solubility for YVO 4, low viscosity, low vaporization without toxicity (in the 1200–1400°C working temperature range), and the oxygen deficient Li-V bronze (γ-LiV 2O 5) can easily form in it, thus preventing oxygen defect formation in the yttrium vanadate crystals. Wanklyn's model and Viting and Timofeeva's calculation data were applied successfully for preliminary selection of the flux material. From the schematic V 2O 5-Li 2O-V 2O 3 ternary and Y 2O 3-V 2O 5-Li 2O-V 2O 3 quaternary systems, the phase relations of Li-V bronzes and YVO 4 can be resolved much more easily than from the previous simple binary systems. The transparent, macro-defect-free single crystal sample grown by the TSSG technique illustrates the significance of these considerations and the promise of this growth technology for YVO 4 crystals.

Growth Studies of YVO4 Crystals: I. Aspects of Oxygen Deficiency

AbstractDuring crystal growth of yttrium orthovanadate (YVO4) from the Y-V-O melt system, strong incongruent vanadium oxide vaporization occurs, causing changes in both oxygen and Y/V stoichiometry and resulting in significant color centers and inclusion problems in the crystal. Oxygen deficiency is an inherent problem in melt grown YVO4 crystals, and this work seeks to clarify this phenomenon. Lattice parameter decrease was observed in oxygen deficient YVO4-x fibers grown by the laser heated pedestal growth (LHPG) technique. Although post-growth annealing in O2 atmosphere can eliminate the black color centers in the fibers, it causes anisotropic lattice distortions within the crystal. Consequently, preventing the formation of oxygen deficient YVO4-x holds the most promise for production of scattering free YVO4 crystals. Since the complete suppression of incongruent vaporization is very difficult during high temperature growth procedure, utilization of a proper flux system having a low melting temperature “compensating phase” for collecting non-pentavalent vanadium oxides is recommended to achieve directly-grown oxygen deficiency free yttrium orthovanadate crystals.

ChemInform Abstract: Preparation of Alkoxy‐Derived Yttrium Vanadate.

AbstractHydrolysis of an ethanolic yttrium vanadyl ethoxide solution (prepared by addition of NaOEt to a solution of VO(OEt)3 and YCl3 in EtOH and removal of NaCl) yields either crystalline YVO4 (host material for red phosphors) or an amorphous product depending on the Y2O3:V2O5 ratio.

Preparation of Alkoxy‐Derived Yttrium Vanadate

The compound formation in the system has been studied by the alkoxy‐method. Crystallized is prepared by the simultaneous hydrolysis of yttrium and vanadyl alkoxides, followed by washing and drying. The chemical structure is described by the formula . The as‐prepared powder gives large aggregates of fine particles. Specific surface areas of powders heated at low temperatures are very high. Solid solutions of containing up to 20 mole percent crystallize slowly at ≈450° to ≈1000°C from amorphous materials. The values of the lattice parameters increase linearly with increasing content. The compounds and are formed by transformation of solid solution. A new modification of the former compound is found.

Infrared luminescence spectrum and crystal-field analysis of neodymium-doped yttrium vanadate

The 4F 3 2 → 4I 9 2 4I 11 2 , 4I 13 2 , 4I 15 2 luminescence spectra of Nd 0.001 Y 0.999VO 4 have been recorded at temperatures down to that of liquid helium and are analyzed in detail. Luminescence is reported for the first time from the 4F 5 2 level, which is thermally populated from 4F 3 2 . New assignments are given for energy levels from the 20 K visible absorption spectrum of the same material. From these results, forty-eight levels are fitted by varying twelve parameters with arms energy deviation of 10.3 cm −1. Vibronic sidebands are reported from the luminescence of HoVO 4 and YVO 4: Ho 3+, corresponding to the excitation of single quanta of internal vanadate and lattice modes.

Preparation of alkoxy-derived YVO 4

Yttrium vanadate, YVO 4, is prepared by the simultaneous hydrolysis of yttrium and vanadyl alkoxides, followed by washing and drying. The chemical structure is described by the formula Y (VO 4). The as-prepared YVO 4 powder gives large aggregates of fine particles. Specific surface areas of powders heated at low temperatures are very high.

Vanadia reactions with yttria stabilized zirconia

The reaction of vanadia films with yttria stabilized single-crystal cubic and polycrystalline cubic-tetragonal zirconias was studied using Rutherford backscattering (RBS) and x-ray diffraction, with some selected depth profiling studies. Vandium on zirconia readily oxidizes at 500 °C to form vanadia films. With increasing temperature, small amounts of vanadia diffuse into the zirconia. Near 650 °C the vanadia forms a eutectic solution at the surface and massive diffusion into the ZrO2 occurs. With rapid heating much of the vanadia volatilizes; with slow heating the vanadia diffuses large distances into the zirconia. Near 800 °C the vanadia principally reacts with yttria to form yttrium vanadate. At 980 °C and above, vanadia is completely reacted. Zirconia coated with materials which do not form a eutectic mixture (tantala, tantalum, vanadium) showed little reaction or diffusion at 900–1000 °C, but massive dissolution when a eutectic is formed (vanadia, chromia+vanadia). Yttria preferentially diffuses toward the surface when a reaction takes place to form YVO4 . When yttria is sequestered as the vanadate, the zirconia changes phase from cubic to monoclinic. Little difference in reactivity is observed between single-crystal and polycrystalline zirconia due to eutectic solution formation, which, with the phase separation, produces a very corroded surface.

A high-pressure Raman study of yttrium vanadate (YVO 4) and the pressure-induced transition from the zircon-type to the scheelite-type structure

The pressure dependences of the Raman active modes in yttrium vanadate (YVO 4) crystallizing in the zircon-type structure D 4 h 19 ( I4 1 amd ), have been studied using a diamond anvil cell up to 15 GPa. At room temperature the zircon-type structure transforms to the scheelite-type structure C 4 h 6( I4 1 a ) with a = 5.04 Å and c = 11.24 Å near 7.5 GPa. The density changes from 4.24 to 4.74 g cm 3 in the transition, and the corresponding volume decrease is Δ V = 5.07 cm 3 mole . The high-pressure phase is retained on release of pressure. The optical absorption edge shifts from 3.87 to 2.77 eV at the transition, presumably due to charge transfer, or due to V-O bond length change of the VO 4 tetrahedra. The internal mode frequencies of the VO 4 tetrahedra also decrease abruptly at the transition. The V-O bond stretching frequency decreases from 891 to 828 cm −1 in the scheelite-type phase, which suggests a fundamental change in the VO 4 unit. The general question of the stability of the zircon-type structure under high pressure is discussed in the light of the high-pressure behavior of a large number of rare earth vanadates and arsenates.

The effects of crystal field on Nd(su3+) in the laser host YVO(in4)

The behavior of Nd 3+ in the laser host yttrium orthovanadate, YVO 4, has been investigated with respect to its absorption spectra By taking into consideration intermediate coupling, a new set of crystal field parameters is obtained which gives a lower rms deviation between observed and calculated energies for 25 of the 26 levels of the 4 I term than that reported earlier using a pure Russell-Saunders basis. The computed g-factors are also in good accord with resonance results Vanous quantities including the nuclear hyperfine parameters have been calculated Nuclear properties which depend on the crystal field are predicted for both the isotopes of Nd

Increased Red Output, Low Color Temperature Metal Halide Lamps

By means of a phosphor coating, metal halide lamps have been developed with a color temperature of 3200 °K initially, that average about 3000°K through life. Increased red emission is achieved by use of a two-phosphor coating, one being yttrium vanadate that absorbs primarily ultraviolet radiation, the second being magnesium fluorogermanate that absorbs primarily blue radiation. Three wattages of horizontal lamps have been developed: 175W, 250W, and 400W, all of which operated within ten minimum perceptible color differences (MPCD) of a common chromaticity specification. With the phosphor coating, lamp efficacy is reduced 6 to 8 percent below that of the comparable clear lamp.

Excited states in yttrium orthovanadate studied by electron-energy-loss spectroscopy and x-ray photoelectron spectroscopy

An analysis of the possible excitations in the outer part of the electronic structure of YV${\mathrm{O}}_{4}$, based on the measurement of the characteristic electron-energy losses and x-ray photoelectron spectra is presented. The loss structures below 12 eV and above 22 eV are consistent with the molecular-orbital diagram of the oxyanion V${\mathrm{O}}_{4}^{3\ensuremath{-}}$ obtained within the cluster-model approach. Plasmonlike collective excitations are found at an energy some 5 eV below the "free-valence-electron" value. Deeper O $2s$ electrons appear to be excited by electrons preferentially not in single-loss events, but together with some molecular orbitals or plasmons. Deeper V $3p$ electrons are also excited, with losses that exceed by a few eV the binding energies of these electrons. Yttrium states are found in the photoelectron spectra, but their excitation by electrons, although possible in principle, is not supported by our data.

Improved Mercury Lamp for Low Color Temperature Applications

Mercury lamps with a warm tone appearance (correlated color temperature about 3300°K) typically operate at an efficacy well below that of the cooler deluxe mercury lamp (color temperature about 4000°K). To improve the warm mercury lamp blends of cerium activated yttrium aluminum garnet phosphor with europium activated yttrium vanadate phosphor have been studied. Calculations using a computer simulation were used to predict the effect of the individual phosphors on the chromaticity and efficacy of the lamp. With a 35 percent by weight YAG: Ce phosphor blend, 400-W mercury lamps have been made with 23,500 Im, 3350°K color temperature and a color rendering index of 48. Lamps of this formulation have been found satisfactory in maintenance and field test applications.

On the luminescent behaviour of europium in yttrium oxide and yttrium vanadate hosts

Europium-doped Y2O3 and YVO4 were excited by ultraviolet and 10 kV electrons to give the red emission of Eu3+. Increase in the fluorescence output with temperature under uv excitation results from an increased absorption and a more efficient energy transfer to the Eu3+ ions from charge-transfer states involving the Y-O and V-O componensts of the lattices. The absence of thermal quenching of fluorescence for (Y2O3∶Eu) is attributed to the high energy of its charge-transfer states which forbids the5D0 state to come into thermal contact with them. Complete quenching would occur above 2000 K as predicted from an estimated activation energy of 24 417 cm−1. Quenching of cathodoluminescence of (YVO4∶Eu) commences at 150 K due to the lower energy of its charge-transfer states. The experimentally-deduced temperature for complete quenching of cathodoluminescence for (YVO4∶Eu) is lower than that predicted from an estimated thermal activation energy of 14 217 cm−1; the difference being attributed to localized heating effects induced by electron bombardment. It is suggested that europium ions do not take part in thermoluminescence processes. Electron-hole recombinations occur at host sites to give the observed glow peaks which have been ascribed to traps produced by lattice defects and uncontrollable impurities in the undoped hosts.

Spectra of europium-doped yttrium oxide and yttrium vanadate phosphors

The spectral distributions of the visible absorption and fluorescence emission under electron beam excitation of Eu3+-doped (Y2O3) and (YVO4) powders have been detected and analyzed. (Y2O3: Eu3+) has a cubicC crystal structure with a unit cell dimension a=10·61 A. Its observed transitions from7 F 0 to many upper states have been recognized; the observed number of Stark components is in agreement with that based on theC 2 site symmetry of the Eu3+ ion in Y2O3. Eu3+-doped yttrium vanadate has a typical zircon tetragonal crystal structure with unit cell dimensions ofc=6·29 A anda=7·11 A. The observed transitions in (Eu3+: YVO4) have been identified and assigned in accordance with theD 2d site symmetry of the Eu3+ ion in this lattice.