Vanadate phosphors

Phosphoric, Vanadic, Arsenic, and Antimonic Acids —Nitrous, Phosphorous, Arsenious Acids—Phos-phatic Acid—Iiyponitrous and Hypophosphorous Acids, and their Saits. 

Europium oxide is now widely used as a phospor activator and europium-activated yttrium vanadate is in commercial use as the red phosphor in color TV tubes. Europium-doped plastic has been used as a laser material. With the development of ion-exchange techniques and special processes, the cost of the metal has been greatly reduced in recent years. 

Some oxide-type minerals have been found to luminesce when irradiated. A simple example is ruby (aluminium oxide with chromium activator), which emits bright-red light. The phosphors are incorporated into colour television screens to emit the colours blue (silver-activated zinc sulphide), green (manganese-activated zinc orthosilicate), and red (europium-activated yttrium vanadate). 

Vanadium usually is recovered from its ores by one of two processes, (1) leaching raw mineral with hot dilute sulfuric acid, and (2) roasting ore with common salt to convert vanadium into water soluble sodium vanadates. In the sulfuric acid leaching process, vanadium is extracted from acid leach liquors by solvent extraction with an aliphatic amine or an alkyl phosphoric acid in kerosene. The organic solvent extract then is treated with an aqueous solution of ammonia in the presence of ammonium chloride to convert vanadium into ammonium metavanadate. Alternatively, the organic extract is treated with dilute sulfuric acid or an aqueous solution of soda ash under controlled conditions of pH. Vanadium is precipitated from this solution as a red cake of sodium polyvanadate. 

AIPO4-5 molecular sieve (BET surface area, 299 m g ) used in this study was prepared by the method of Wilson et al. [1j. VjOg/AIPO -S samples were prepared by impregnating with aqueous solutions of ammonium vanadate after removing templating agent in the AIPO -S by calcining at 530°C. The samples were dried at 110 C for 24 h then calcined in air at 550°C for 2 h. VAPO -S was prepared from gel mixture of phosphoric acid, pseudoboehmite, vanadium pentoxide, tri-propylamine and water (1.3 PrjN x AljOj PjOj 40 HjO) by crystallization at 165°C for 3 - 7 days [7. ... 

Most of the successful rare earth activated phosphors comprise host lattices in which the host cation is also a rare earth. A principal reason for this relates to the optical inertness of La, Gd, Y, and Lu this is essential to avoid interference with activator emission spectra. Close chemical compatibility including amenability to substitutional Incorporation of rare earth activators are also essential features. Rare earth hosts such as oxides, oxysulfides, phosphates, vanadates and silicates also tend to be rugged materials compatible with high temperature tube processing operations and salvage. 

Although a variety of synthesis, compositions and reactor parameters were studied, the P-V-0 catalysts in the temperature series were synthesized in the up flow HTAD reactor using a 0.12 M solution of anunonium vanadate in water which contained the required amount of 85% phosphoric acid to result in a 1.2/1.0 P/V atom ratio. This atom ratio is normally preferred for the most selective oxidation of butane to maleic anhydride. Table I shows that the P/V atom ratios obtained for the analyzed, finished (green colored) catalysts were approximately the same as the feed composition when a series of preparations were studied between 350 C and 800°C. This was typical for all of the catalysts synthesized under a variety of conditions. 

Europium satisfies the needs of both red and blue phosphors. Typical materials used for the former are europium yttrium vanadate and yttrium oxysulphide doped with europium. Blue... 

Lwteo Series.—These are prepared by adding excess of phosphoric acid to solutions of alkali vanadates. The following are known —4... 

Colorimetric Methods are used only for the estimation of very small percentages of vanadium, e.g. in vanadium steels and alloys. The most important depend on the intensity of the reddish-brown colour produced by the action of hydrogen peroxide on an acid vanadate solution.3 If chromium is present, an equal amount must be introduced into the standard vanadium solution under the same conditions of temperature, acid concentration, etc. Phosphoric acid is added to destroy any yellow colour due to ferric iron, and either hydrofluoric acid or ammonium fluoride to destroy any colour produced by titanium.4 A colorimetric method for the simultaneous estimation of small quantities of titanium and vanadium has also been worked out.5 Other colorimetric processes are based on (a) the formation of a yellow to black coloration, due to aniline black, in the presence of aniline hydrochloride and potassium chlorate or other oxidising agent,6 and (b) the orange coloration finally produced when an acid solution of a vanadate is brought into contact with strychnine sulphate.7... 

The Srs(P04)3Cl crystals are hexagonal needles with lattice parameters ah = 9.953 A. and ch = 7.194 A. The needle axis corresponds to the crystallographic c axis. The europium(II) doped sample is a phosphor, readily excitable with electrons, x-rays, and both short and long ultraviolet light. It emits in the blue with a peak at 445 nm. Crystals of strontium chloride vanadate(V) are orthorhombic platelets with lattice constants a = 7.43 A., b = 11.36 A., and c = 6.54 A., with the b axis corresponding to the thin dimension of the flakes. Strontium chloride vanadate(V) is a self-activated phosphor giving broadband emission with a peak at 423 nm. when excited with 2537-A. radiation. All compounds are insulators, with resistivities >1012 ft-cm. 

An example of a coding phosphor is yttrium vanadate which is activated by trivalent rare earths. In another invention, that of Andersson (Ref 12), Ca silicate powdr of less than 6mm particle size is suggested for use as an adsorbing... 

Phosphates, arsenates, and vanadates contain a simple molecule of oxygen combined with phosphorous, arsenic, or vanadium. Compounds of P04 are most common. Although this is the largest group of non-silicate minerals, only a few of them are found in museums outside of mineral collections. The most notable exception is turquoise, a phosphate of copper. Variscite is a blue-green phosphate sometimes used as an imitation of turquoise. Callais is variscite from Spain and France that was used in the Early Neolithic as a pigment and to make trade beads. 

Scott [48] has determined europium in yttrium phosphors. Yttrium vanadate (0.1 g) was fused with potassium carbonate (2g) in a platinum crucible. Yttrium oxide and yttrium oxysulphide can be dissolved directly in the same solvent as the above melt, 50% hydrochloric acid. Standard flame conditions for yttrium were used. 

Chromates, vanadates, and cerium salts give colour reactions with the reagent and should therefore be absent. Iron salts give a yellow colour with hydrogen peroxide, but this is eliminated by the addition of syrupy phosphoric acid. Fluorides bleach the colour (stable [TiF6]2 ions are formed), and large amounts of nitrates, chlorides, bromides, and acetates as well as coloured ions... 

So far neither work of phosphor films via the Pechini-type sol-gel proeess nor their direct patterning via soft lithography have been reported in literature. Yttrium vanadate (YVO4) has been shown to be a useful host lattice for rare earth ions to produce phosphors emitting a variety of coIors[7]. In this paper, we report a Pechini sol-gel synthesis of the nanocrystalline YV04 A (A=Eu, Sm, Er ) thin phosphor films and their... 

Among numerous rare earth vanadate compounds, YV04 Eu has been investigated most for its value in practical use. Its bulk polycrystals could reach a quantum yield (QY) of ca. 70% as commercial red phosphor. Huignard et al. obtained 7-YV04 Eu " NPs with sizes around 15-30 nm... 

Hydrothermal routes Under ambient conditions, the low reaction temperature and fast precipitation rate have deleterious effect on the crystallization and optical performance of rare earth vanadate nanomaterials. Referring to traditional solid-state reactions, bulk YV04 Eu phosphors require a calcinations temperature above 1300 K, but it is too high for the preparation of nanomaterials. Alternatively, hydrothermal routes could provide the adequate energy for solution phase reactions, which have been widely described in preparation of ceramic powders. The high pressure and temperature largely promote the dissolution-reprecipitation process, so as to decrease the lattice defects of NCs. With fine modulation, this method is also efficient to produce nano-sized crystals. 

Multicolored luminescence is the most attractive property of rare earth-based compounds. Lanthanide ions possess many sharp emission lines that cover the visible and near infrared (NIR) region due fo fhe abundanf fransifions of f-orbital configurations. However, the forbidden f-f fransi-fions induce narrow excitation lines for mosf rare earfh ions. This low absorbency cross-section is the bottleneck in practical application, so host-sensitized emission mode is commonly employed by rare earth phosphors. The vanadate matrix is one of fhe candidafes, which excifes lanthanide ions via charge-transfer energy migration. 

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