A. Vecht

Control of Y 2 O 3:Eu Spherical Particle Phosphor Size, Assembly Properties, and Performance for FED and HDTV

The preparation of spherical phosphor particles that are monosized for a given set of conditions, are described. The nature of the resulting self‐assembled and close packed phosphor spherical particles appears to be very promising for both field emission devices (FED) and high definition television (HDTV). The size of the particles can be controlled by careful manipulation of the experimental conditions, the rationale behind this is discussed. The luminescent efficiency of the particles as a function of particle size is also reported. It is demonstrated that good light output is possible from nanocrystals.

Engineering phosphors for field emission displays

Factors affecting the synthesis and properties of a new generation of fine particle low voltage phosphors in field emission displays are reviewed. The morphology and particle size, the composition and stoichiometry, the stability, together with the nature and shape of the particle surface, all play important roles in the performance of the final phosphor. Initial new results from novel synthetic methodology are presented and discussed. Their implications in the light of the known literature point the way to the successful conclusion of the current thrust of phosphor research for good red, green, and blue low voltage, high definition phosphors.

SUBMICRON-SIZED SPHERICAL YTTRIUM OXIDE BASED PHOSPHORS PREPARED BY SUPERCRITICAL CO2-ASSISTED AEROSOLIZATION AND PYROLYSIS

The synthesis of Eu(III)- and Tb(III)-doped yttrium oxide phosphor powders by supercritical CO2-assisted aerosolization and pyrolysis (at 1010 °C) from aqueous solutions of Y(NO3)3, Eu(NO3)3, and Tb(NO3)3 is presented. Dense, submicron aerosols are formed by contacting aqueous solutions of the precursor metal nitrates with supercritical CO2 at 1500 psi, and decompressing the mixture through a restrictor nozzle into a heated tube. X-ray diffraction data indicate that the powders are crystalline, and consist of a single phase. Scanning electron microscope shows that they are spherical in morphology and less than 1 μm in size with average diameters of ∼0.2 μm. The cathodoluminescence intensity of the Y1.91Eu0.09O3 powders, annealed at 1200 °C for 1 h, is more than twice greater than that of the industrial standard (P56, 3–10 μm in diameter) phosphor. The phosphors synthesized by this method are promising candidates for use in high-resolution low-voltage flat panel displays.

Cathodoluminescence studies of yttrium silicate:cerium phosphors synthesised by a sol–gel process

Sol–gel chemistry has been used to produce a Y2SiO5:Ce phosphor with good chromaticity and brightness. Although, the chromaticity of Y2SiO5:Ce1% was similar to that of a commercial Y2SiO5:Ce phosphor, it was B20–25% brighter. Yttrium silicate:cerium phosphors that contained a range of gadolinium concentrations were also prepared by the sol– gel route, and their luminescence properties under cathodoluminescent conditions were measured. Over the range of gadolinium concentrations, there was no significant change in the chromaticity of the phosphors, but the addition of gadolinium resulted in a B20% loss in brightness compared to Y2SiO5:Ce1% synthesised by the sol–gel route. r 2002 Elsevier Science B.V. All rights reserved.

The Synthesis of Fine Particle Yttrium Vanadate Phosphors from Spherical Powder Precursors Using Urea Precipitation

Spherical precursors to YVO 4 phosphors are reported that lead to fired materials of 1-5 μm in size with the majority of particles below 4 μm. The photoluminescence performance of the phosphors prepared by this method is as good as those of commercial phosphors, where the average size particle has a volume nine times greater than those reported here. The excitation and emission spectra for YVO 4 :M (where M = Bi 3+ , Th 3+ , Eu 3+ , Sm 3+ , or Er 3+ ) are presented. The origins of the emission in YVO 4 are briefly discussed.

Narrow band 390 nm emitting phosphors for photoluminescent liquid crystal displays

Photoluminescent liquid crystal displays use a liquid crystal to modulate the intensity of ultraviolet light incident on visible emissive phosphors. In order to gain optimum performance from the liquid crystal in such a device, the activating light must cover a narrow spectral bandwidth very near to the visible (violet) region of the spectrum. Calcium sulphate europium phosphor offers an emission spectrum closely matching these requirements and has been incorporated inside low pressure mercury cold cathode fluorescent lamps. These have been used to backlight a photoluminescent liquid crystal display demonstrator.

A Novel Method for the Synthesis of ZnS for Use in the Preparation of Phosphors for CRT Devices

The decomposition of thiourea dioxide in aqueous solution at elevated temperatures, in the presence of zinc acetate, has been used to precipitate ZnS. The important reaction pathway for the formation of sulfide ions has been elucidated, and some common ZnS S phosphors have been prepared from the precipitate. The preparation of ZnS by this method is extremely simple and does not yield large amounts of liquid or gas containing volatile sulfur species Thus, this method has been shown to be an excellent method for the preparation of ZnS phosphors, particularly copper-activated materials, requiring no purification of the reagents, with little production of sulfur-containing waste species, and resulting in small particle size powders without postproduction milling or separation of the powders. These phosphors have been shown to have exceptional luminescent properties compared to standard commercial materials.

A Novel Method for the Preparation of Inorganic Sulfides and Selenides. I. Binary Materials and Group II–VI Phosphors

A novel method for the synthesis of wide range of metal sulfides and selenides is described. Polysulfide solutions formed by the dissolution of sulfur in hydrazine monohydrate have been shown to contain the hexasulfide and tetrasulfide anions. The action of these solutions, or their selenium analogues, with a range of transition and main group metal salt solutions yields a precipitate, which after firing at an elevated temperature, forms a crystalline metal sulfide or selenide. This method of preparing metal chalcogenides has been extended to some group II-VI phosphors with promising luminescent properties.

Visible electroluminescent subwavelength point source of light

A structure has been devised to generate a visible point source of electroluminescently produced light with subwavelength dimensions. This submicron (0.3 μm) spot of light is created by the combination of a standard dc electroluminescent powder, ZnS:MnCu, that is introduced into the tip of a glass micropipette coated with a transparent coating of conducting indium oxide as the anode and an appropriate electrode placed inside the pipette as the cathode.

A Method for the Clean Syntheses of Sulfides/Selenides II. Ternary Sulfides/Selenides

The syntheses of MGa 2 S 4 (where M = Ca, Sr, and Zn), CuMS 2 (where M = In or Cr). Ba 2 ZnS 3 , and CuInSe 2 by utilizing sulfur or selenium solutions in hydrazine monohydrate are reported. Scanning electron microscope studies of the morphology of the resulting materials prepared by this route are presented. The photoluminescence spectra of the phosphors SrGa 2 S 4 :Eu. SrGa 2 S 4 :Ce, ZnGa 2 S 4 :Mn, CaGa 2 S 4 :Eu, and Ba 2 ZnS 3 :Mn are displayed. The method is more environmentally friendly than traditional preparations (very little sulfur-based gases are formed). Additionally, it is a simple and rapid preparation, producing a good yield. The procedure facilitates the formation of ternary metal sulfides or selenides. It is further shown that for optimum performance of SrGa 2 S 4 :Eu, the phosphor needs to be fired in a reducing atmosphere to convert all of the Eu 3+ to Eu 2+ .