Terry G. Ireland

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.

Novel nano-structured phosphor materials cast from natural Morpho butterfly scales

The fabrication of the first nano-structured phosphor materials, cast from scales of the Morpho pleides butterfly, are reported. The structures are obtained by infilling sections of the butterfly wings with precursor phosphor solutions, then drying the samples at 100°C, followed by firing/annealing at 700°C for 30min. During the firing of the resulting solids the natural template is sacrificed and burns off, leaving a cast of the butterfly structure that is composed of the resulting phosphor material. Two different phosphor precursor solutions were used, either the precursor water-based solution for the red Y2O3:Eu3+ phosphor or europium-doped titanium ethoxide solution, which is the precursor for the TiO2:Eu3+ phosphor. In this work we have demonstrated that it is possible to reproduce fine detail in these casts, with structural features having ca. 100 nm dimensions being clearly visible. The casts of two distinct types of scale of the Morpho pleides butterfly were prepared in this work from phosphor materials. One distinct type of scale was rounded whereas the other was dentated, there being a clear difference in spacing between the longitudinal ridges for these two types. As yet, the casts manifest none of the photonic properties of the original butterfly scales. This is thought to be due to the precursor phosphor solutions not penetrating into the lamellar structures that are located between the cross-ribbing in the scales.

Fine Control of the Dopant Level in Cubic Y 2 O 3 : Eu3 + Phosphors

It is demonstrated that the use of urea to control the pH, and thereby the point of precipitation for the metal hydroxycarbonate phosphor precursor (once the concentration of reactants reach supercritical saturation), facilitates complete removal of all the activator ions from solution over a very wide concentration range (i.e., from 0.2 mole fraction Eu 3+ to 5 × 10 -7 mole fraction Eu 3+ ); all these ions become incorporated into the precipitated phosphor precursor material. Moreover from the evidence it appears that the activators are very evenly and homogeneously distributed in the final phosphor particles so the method gives rise to atomic mixing in the original initial solutions.

Photonic phosphors based on cubic Y2O3:Tb3+infilled into a synthetic opal lattice

Studies on a cubic Y2O3:Tb3+/SiO 2 inverse photonic lattice are reported. The method of preparation of the phosphor photonic lattice is described in detail. Scanning electron micrographs showed that the SiO2 spheres had an oxide coating of ~40 nm thickness in the final material. Optical micrographs of the final synthetic opal crystal infilled with cubic Y2O3:Tb3+ phosphor clearly show that the crystal rejected green light. It is shown that the crystal rejects green laser light but can be excited by 253.7 nm light, though the intensity of its green emission is strongly modulated by the presence of a stop-band at 559 nm (calculated by assuming complete filling of the voids in the template). Evidence is also presented to show that in such a photonic solid quenching of the luminescence does not take place at the same temperature as in the bulk solid.

A Synthetic Method for the Production of a Range of Particle Sizes for Y 2 O 3 : Eu Phosphors Using a Copolymer Microgel of NIPAM and AMPS

A novel method for preparing the cathodoluminescent red europium-doped yttrium oxide (Y 2 O 3 :Eu) phosphor using the copolymer microgel of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) is described. An extensive range of spherical particle sizes can be produced by careful manipulation of the experimental conditions. Spherical particle size is shown to be directly controlled by the quantities of copolymer microgel, allowing spherical particles for a given size from 0.1 to 1.3 μm to be produced. The luminescent intensity of the particles related to the particle size is also reported.

Facile method of infilling photonic silica templates with rare earth element oxide phosphor precursors

A method for preparing rare-earth element-doped yttrium oxide phosphor photonic band gap crystals (PBG) is described, which obviates the necessity for multiple infilling of the opal-like template. The method utilizes (i) the re-dissolving and the concentration of previously precipitated spherical phosphor particles made by homogeneous precipitation methods into a viscous precursor phosphor solution, and (ii) formation of an opal-like template of polystyrene or silica spheres. A procedure is outlined that permits the precursor solution to be drawn into the template in a controlled manner that can be easily monitored using an optical microscope. Attenuation of the strong, red cathodoluminescent emission is observed in Y 2 O 3 :Eu 3 + phosphor PBG crystals that are engineered to have a stopband overlapping the emission bands in the red region. This attenuation results from Bragg diffraction of the light emitted within the PBG phosphor crystals.

AC powder electroluminescent displays

Abstract— The current status of AC powder electroluminescent (ACPEL) displays is reviewed with particular emphasis given to color and lifetime. The printing of the displays in forward and reverse architectures is also discussed, in addition to the fabrication of ACPEL displays with interdigitated electrodes, and different types of ACPEL phosphors and materials for back electrodes, transparent conducting electrodes, binders, and dielectrics are considered. Furthermore, shape conformable and highly flexible ACPEL displays are surveyed.

Structure and Morphology of ACEL ZnS:Cu,Cl Phosphor Powder Etched by Hydrochloric Acid

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Rare-earth element anti-Stokes emission from three inverse photonic lattices

The fabrication of a two-dimensional photonic lattice of ZrO2:Er3+ on a silicon substrate and two three-dimensional photonic lattices, ZrO2:Eu3+ and TiO2:Er3+, are described. It is demonstrated that, for the two-dimensional lattice, photonic properties dependent on the lattice are not present, although another effect that was dependent on the structure is discussed. For the two three-dimensional photonic lattices, the position of the photonic stopband relative to the emission bands of the anti-Stokes phosphors is shown to be crucial in controlling emission properties. In the case of the ZrO2:Eu3+ lattice, where the stopband was close to both the emission and the exciting wavelengths, the intensities of both were affected. However, for the TiO2:Er3+ lattice, where the stopband was far from the exciting and emission wavelengths, no such effect was seen. It was concluded from this work that it should be possible to prepare unconverting photonic lattices with stopbands that extend the lifetimes of certain excited states by inhibiting spontaneous emission from them, thereby facilitating enhanced upconversion efficiency.