Dominic A. Davies

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.

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.

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+ .

Synthesis and nonlinear optical properties of a range of 1-ferrocenyl(2-(4-alkyl)pyridiniumyl)ethylene iodides

Abstract The preparation of a range of compounds of general formula FcCHCHC 5 H 4 N + X, where X=C n H 2 n +1 ( n =1–5, 10 or 18) and O − , was achieved via condensation of the relevant picolinium iodide with ferrocene carboxaldehyde. The spectroscopic properties of these materials were shown to be very similar, however the SHG, measured by the Kurtz powder technique, showed that increasing the alkyl chain above three carbons resulted in a dramatic loss of SHG efficiency. The O − compound also yielded very little SHG.

Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 5. An interpretation of the 57Fe Mössbauer spectroscopic data of dibromoborylferrocenes, and related molecules

Abstract The Mossbauer spectroscopic parameters of three dibromoboryl ferrocenes and of a related dichloroboryl ferrocene are reported. The results are discussed in relation to the known crystal structures, the Mossbauer parameters and the correlation of the latter with Hammet substituent constants. These data are also compared with those of other ferrocenes that form ferrocenyl carbocations (–CR 2 + is isoelectronic with –BX 2 where X=halogen) as well as protonated ferrocenyl ketones. It is concluded that normal ferrocenyl carbocations, though nominally isoelectronic with the similarly substituted dibromoboryl ferrocenes, bond in a very different manner involving a change in structure where the two cyclopentadienyl rings are no longer parallel. However, the protonated ferrocenyl ketones show Mossbauer quadrupole splittings that are similar to those of the dibromoboryl ferrocenes; this is interpreted to suggest that the former cations have significant carbocationic character and parallel cyclopentadienyl rings. The nature of the Fe–B interactions are discussed in terms of the overall C–B bonding, particularly in the case where four dihaloboryl groups are present.

49.1: Improved Zinc-Sulfide-Type Phosphors by a Novel Synthetic Method

A novel, quick, and “clean”, method has been developed for the preparation of zinc sulfide phosphors for CRT and FED applications. The method involves the addition of a solution of sulfur in hydrazine monohydrate to a zinc salt solution, which results in precipitation of zinc sulfide, Firing this material has resulted in bright, efficient phosphors with improved luminescent properties between 500–15,000 eV, particularly for copper and silver activated ZnS.

L-2: Late-News Paper: A Novel Low Cost Binder for Flexible AC Powder Electroluminescent Panels

A novel binder for AC powder EL displays has been developed. This was used to form very pliable low cost EL displays which require no additional dielectric reflector layer. The emissive layer can be peeled from the substrate giving a very flexible film which is still EL active when placed between two electrodes. This EL film could be shaped as desired.

Topotactic crystallisation of calcite under hydrothermal conditions

It is shown that control of the phase of calcium carbonate produced during hydrothermal crystallisation can be achieved by the use of titania as a catalyst. In this work it was demonstrated that if either amorphous or the rutile phase of titania is added the aragonite polymorph of calcium carbonate is produced to the exclusion of all other phases. When anatase is the major titania form present then the calcite phase of calcium carbonate is favoured though some aragonite is still produced. The selectivity towards calcite is enhanced by increasing the hydrothermal processing temperature from 120°C to 135°C. It is suggested that the titania phase present catalyses the crystallisation by providing nucleation sites for the calcium carbonate to grow from.

How to stop a molecular rotator. Mössbauer spectroscopic studies on (η-benzene)(η-cyclopentadienyl)iron(II) hexafluorophosphate in the presence and absence of high pressure

Application of a pressure of 1.79 GPa, at room temperature on (η-benzene)(η-cyclopentadienyl)iron(II) hexafluorophosphate is shown to arrest the dynamic reorientation of the cations; the effect of pressure is studied using Mossbauer spectroscopy.