G. R. Fern

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. 100u2009nm 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.

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.

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.

Up-conversion emission phosphors based on doped silica glass ceramics prepared by sol–gel methods: control of silica glass ceramics containing anatase and rutile crystallites

Using sol–gel methods novel silica based glass ceramics containing TiO2, Er3+ and Yb3+ ions have been prepared. Anatase and rutile crystallites composed of TiO2, Er3+ and Yb3+ ions that segregate in the glasses have been shown to be new yellow emitting up-converting materials. It is demonstrated that by annealing SiO2 glasses containing TiO2, Er3+ and Yb3+ ions, crystals of either the anatase or rutile phases can be grown in the glass (dependent on annealing temperature). Laser Raman spectroscopy is shown to be a useful technique to characterise the crystallographic phases in the pure state, and in these new ceramics. Furthermore, their emission can be excited at a wavelength of 632.8xa0nm, and the up-converted luminescence in the visible region can be detected and monitored using a Raman spectrometer.

4.3: Factors Affecting Efficiency in Submicron Phosphors: Implications for Screens for High Definition Displays

Studies on phosphor particles in the range 0.05 to 0.35µm prepared from spherical particle precursors provide strong evidence that the main factors affecting light output are crystallinity, orientation, of the crystallite, and space between particles (in close packed arrays). These findings should be applicable to all high resolution phosphors.

A new oxide/oxysulfide based phosphor triad and high-efficiency green-emitting (Y,Gd)2O2S:Tb phosphor for FED applications

An oxide/oxysulfide based phosphor triad with particle sizes of around 1micrometer (green Y2SiO5:Tb or Y2O2S:Tb, and blue Y2SiO5:Ce) down to 250nm for the red Y2O3: Eu is reported. These phosphors perform well in brightness under the conditions necessary for use in FEDs and are of suitable size for use in high definition screens. We also report a green emitting Y2O2S:Tb phosphor that has been prepared by a new method involving homogeneous precipitation of the precursors and a new firing regime. The resulting cathodoluminescent phosphor having submicrometer size particles has a luminous efficiency of 34.6 lm/W at an electron beam accelerating voltage of 5000 V.

4.3: A Novel Synthesis of Y2O3: Eu Phosphor Using Carbon Dioxide and Ammonia for High Definition CRT and FED Applications

Phosphor particles of regular shape and size have been synthesised by a new method. Depending on conditions the shape of the particles can be controlled and varied. The particles orient when deposited on screens and display greater luminance at low voltages than commercial and spherical phosphor samples.

P-51: A Novel Synthetic Method for the Production of Y2O3: Eu Phosphor particles of a Controlled Size using Copolymer Microgels of NIPAM

A novel method for preparing the luminescent red Y2O3: Eu phosphor using copolymer microgels of NIPAM is described. An extensive range of spherical particle sizes (from 0.1 to 1 μm) can be produced using copolymer microgels of NIPAM and AMPS. To produce spherical Y2O3: Eu phosphor particles less than 100 nm in diameter, the copolymer microgel used was NIPAM and Acrylic acid (AAc). The dependence of luminescent intensity on particle size is also reported.

UV photoluminescence from small particles of calcium cadmium sulfide solid solutions

Calcium cadmium sulfide solid solutions have been of interest as white cathodoluminescent display materials and microcrystalline UV photoluminescent emission sources for some time. Refinements in the processing of dilute solutions of CdS in CaS have stimulated efforts to gain a greater understanding of the mechanisms giving rise to intense UV photoluminescence. The work presented here is focused on the processing of Ca1−xCdxS in the composition range x = 0.001–0.2 with particular interest in the lower cadmium concentrations. Samples at the latter concentrations were prepared, characterized and found to consist of particles in the size range 50–1000xa0nm. The photoluminescence, excited optimally at 298xa0nm, created a dominant single and symmetrical peak at 370xa0nm (3.35xa0eV) with a FWHM of 65xa0nm for these lower concentrations; this was much sharper than any previously reported work on these materials. The sharpness of the peak appears to coincide with a reduction in particle size. With increasing cadmium concentration, this short wavelength emission band became distorted in symmetry and exhibited a red shift. This was seen as being indicative of a solid solution in which Cd substituted into the Ca sub-lattice. At shorter exciting wavelengths down to 250xa0nm (4.95xa0eV) in Ca0.99Cd0.01S, which was beyond the absorption edge of CaS, the dominant emission peak at 370xa0nm had declined in intensity by two orders of magnitude and was barely perceptible.

4.4: Photonic Phosphor Crystals for Display Applications

It is shown that photonic phosphor crystals potentially offer a number of opportunities for improving photoluminescent, electroluminescent and cathodoluminescent devices. The synthesis of 3-dimensional photonic phosphor crystals is discussed and examples of T.E.M. micrographs and optical diffraction patterns are presented. The modification of the emission properties of these crystals due to their microstructure is discussed.