The field emission characteristics of the Si emitters and the diamond coated Si emitters are investigated. The Fowler-Nordheim plots of the two types of Si emitters show linear slopes. It means that the I-V characteristics follow the Fowler-Nordheim relation. Field emission for the two types of diamond coated Si emitters exhibits significant enhancement both in turn-on voltage and total emission current. The Raman spectrum shows that the high intensity graphite peak is observed with diamond peak and thereby large amounts of graphite may be included in the diamond grain boundary. It seems to be thought that the graphite participates in the low field emission. However, further investigations are needed to understand whether the graphite may enhance the emission characteristics of diamond or not.

Garnet phosphors have potential for use in field emission displays (FEDs). Greenemitting Gd3Ga5O12:Tb (GGG:Tb) and Y3A15012:Tb (YAG:Tb) are possible alternatives to ZnO:Zn, because of their excellent resistance to burn, low-voltage efficiency, (3.5 Im/W from GGG:Tb at 800 V), and saturation resistance at high power densities. Hydrothermal and combustion synthesis techniques were employed to improve the low-voltage efficiency of YAG:Tb, and Y3Ga5O12:Tb (YGG:Tb). Synthetic technique did not affect low-voltage (100–1000 V) efficiency, but affected the particle size, morphology, and burn resistance. The small particle size phosphors obtained via hydrothermal (<1 µm) and combustion reactions (<1 µm) would benefit projection TV, high-definition TV (HDTV), and heads-up displays (HUDs), where smaller pixel sizes are required for high resolution.

The spectral response and outgassing characteristics of the three new, low-voltage phosphors combustion synthesized and electrophoretically deposited for application in field-emission flatpanel displays, are presented. The phosphors, forming a candidate Red-Blue-Green (RGB) triplet are YAG:Eu, YAG:Tb and Y2SiO5:Ce. These cathodoluminescent materials are tested with electron-beam excitation at currents up to 50 x03BC;A within the 200-2000V (eg. "low-voltage") and 3000-8000V (eg. "medium voltage") ranges. The spectral coordinates, as compared with industrially-manufactured P22 phosphors in low voltage operation, are reasonable; however, there is considerable difference in the green coordinates, and the red and green materials show significant satellite intensities. Phosphor outgassing, as a function of time, is measured by a residual gas analyzer at fixed 50 gA beam current in the low-voltage range. We find that after two hours of excitation, levels of outgassed CO, CO2 and H2 stabilize to low values.

A phosphor screen which operates at low excitation energy must show good emission efficiency and sustain stabilities against high vacuum and high current density operation. In this study, low voltage phosphors suitable for FED applications were experimentally addressed and screened onto ITO-glass by the electrophoretic deposition which offers several advantages, including easy control of film thickness and high packing density. Process variables such as deposition rate, salt concentration, etc., in electrophoretic deposition method were optimized to achieve high quality of the screens. Correlations of process variables with particle size, surface morphology and luminescent properties of phosphors will be presented. Particularly, much attention was put on the optimization of phosphor screens for the maximal CL intensities and adhesion of particles over substrate when excited by field emitter arrays.

Degradation of phosphors in field emission displays (FED's) is described and related to electron beam stimulated surface reactions between ZnS and residual gas in the vacuum system. The requirements for producing and maintaining vacuums in FED packages is reviewed and limitations associated with the size of the FED's are discussed. It is concluded that vacuum production and maintenance is critical to the performance of FED's, and this is not a simple task.

We apply a number of complementary characterization techniques including electron paramagnetic resonance, optical absorption, and photoluminescence spectroscopies to characterize a wide range of different ZnO phosphor powders. We generally observe a good correlation between the 510-nm green emission intensity and the density of paramagnetic isolated oxygen vacancies. In addition, both quantities are found to peak at a free-carrier concentration ne, of about 1.4 × 1018 cm-3. We also find that the green emission intensity can be strongly influenced by free-carrier depletion at the particle surface, especially for small particles and/or low doping. Our data suggest that the green PL in ZnO phosphors is due to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band.

In doped nanocrystalline Y203:Tb phosphors the luminescent efficiency was found to increase with the decrease in the particle size from 100 Å to 40 Å. This correlation was obtained from microstructural studies performed using transmission electron microscopy and luminescent measurements.

Cerium activated ternary strontium thiogallate phosphor thin films have been deposited by multi-source evaporation of elemental strontium, gallium and sulfur as source materials. Cerium chloride (CeCI3) has been used as activator starting material. In order to avoid SrS as well as Ga phase segregations elemental In as well as compounds, such as LiF, NaF, LiCl, and SrCI2, have been investigated as possible growth enhancing agents.

Coevaporation of indium resulted in an improved crystallization with the drawback of an increased reabsorption of the cerium emission. The other additives lead to improved crystal quality combined with true-blue cathodoluminescence (CL) performance (C.I.E. color coordinates of up to 0. 14/0.12) which proves phosphor layers without any SrS phase segregations.

Thin film electroluminescent (TFEL) devices with SrGa2S4:CeCl3 phosphor layers prepared with LiF as additive exhibit highest ever reported L40 luminances of 78 cd/m2 and luminous efficiencies of 0.017 lm/W at a transferred charge of 1 μ;C/cm2 with 1 kHz / 50 μs bipolar square wave excitation.

The deposition of CaGa2S4:Ce has been accomplished using a commercial liquid delivery system on two substrate surfaces: ZnS and SrS. However, the film deposited on ZnS was not of satisfactory quality because of the formation of an amorphous layer and a high amount of residual porosity within the deposition. The use of a SrS layer on top of the ZnS improved the nucleation by reducing the interfacial energy between the substrate and deposition. It greatly reduced the porosity in the coating and reduced the formation of the amorphous layer. The crystallinity of the CaGa2S4 400 peak was also increased by a factor of ten when a layer of SrS was used. Further, the FWHM of the 400 peaks from the two depositions was not significantly different, indicating that the crystallite size and strain was approximately the same. The B40 was increased by a factor of two, from 1.84 cd/m2 for ZnS to 3.67 cd/m2 for SrS. This increase is an improvement in the performance of the films and is attributable to the increase in the crystallinity.

A detailed study is reported of the optical properties of homogeneously and δ-doped ZnS:Mn thin films grown by metal-organic molecular beam epitaxy. Fine structure in the Mn luminescence was observed at low Mn concentrations. The energy of the zero-phonon 4T1→6A1, transition of the Mn ion was determined to be 2.215eV, and the phonon energies associated with the transition to be 10meV and 37meV for the TA and TO phonons, respectively. It was found that the PL intensity depended on the Mn concentration and the δ-doped ZnS:Mn showed much brighter luminescence than the homogeneously doped samples with comparable Mn concentrations. For homogeneously doped ZnS:Mn with low Mn concentrations, the temperature dependence of the linewidth and the peak position was well described by the configuration coordinate model. For δ-doped ZnS:Mn, the antiferromagnetic interaction between Mn ions was invoked to explain the low temperature behavior. The luminescence lifetime measurements suggested that the δ-doping technique resulted in better incorporation of Mn ions in the ZnS host and less defect formation.

The electrical properties of titanium dioxide thin films have been stabilised by cerium doping. These films have a high permittivity between 35 to 45 and withstand 650°C. Multilayer TiO2:Ce/CeO2 insulators have been fabricated. The breakdown voltage is increased by a factor 10 with a modest decrease in the permittivity (30 – 35 instead of 35 – 45).

Electroluminescent devices (ELDs) with a classical ZnS:Mn phosphor have been prepared using TiO2:Ce as the first insulator and a TiO2:Ce/CeO2 multilayer as the second insulator. Compared with a standard ELD based on Y2O3 insulators, devices with the new insulators show a significant decrease of the threshold voltage along with a notable increase of the brightness. An important increase is also achieved in the total device efficiency which is maintained over a large range of brightness and transferred charge. Consequences of rapid thermal annealing and conventional thermal treatments on device performance have also been investigated.

Quantum dot composite films, consisting of II-VI nanocrystals imbedded in a ZnS matrix, are candidate phosphor materials for electroluminescent flat panel displays. The optical properties of such composites can be tailored across the visible spectral region by selecting the composition and size of the nanocrystals. We present combined solution chemistry and electrospray organometallic chemical vapor deposition (ES-OMCVD) methods for realizing such composites. Size selected, CdSe quantum dots with an overlayer of ZnS are synthesized in solution. This surface derivatization produces a large enhancement of the photoluminescence efficiency. The quantum dot composites are subsequently formed by introducing the quantum dot solution by electrospray into an OMCVD ZnS thin film process. Photoluminescence and cathodoluminescence properties of the quantum dot composites are reported.

Considerable interest has been generated recently in the application of Porous Silicon to the production of light emitting devices, and a number of demonstration structures have been produced. However, the poor stability of the material pose limitations on its usefulness. We report studies of the luminescence properties of a related, but stable material: silicon-rich silica. This material consists of silicon clusters embedded in a host matrix of silica, and as such is considerably more robust than porous silicon.

We have produced a number of samples of silicon-rich silica thin films by Plasma Enhanced Chemical Vapour Deposition on to doped silicon substrates. We report photoluminescence studies that investigate the nature of the radiative process, and show evidence of two separate luminescence mechanisms: defect luminescence and exciton confinement in nanoscale silicon clusters. Preliminary electroluminescence from silicon-rich silica fabricated by Plasma Enhanced Chemical Vapour Deposition will also be presented.

In this paper, we discuss the effects of electron injection on electroluminescence (EL) efficiency in single-layer EL devices using blends of poly(N-vinylcarbazole) (PVK) and poly(3-nbutyl- p-pyridyl vinylene) (Bu-PPyV). Pure Bu-PPyV thin films suffer from formation of excimers due to the strong interchain interaction. Diluting Bu-PPyV with the high-energy-gap and holetransporting polymer PVK suppresses excimer formation and substantially raises both photoluminescence (PL) and EL efficiencies. The emission color is converted from red to green, indicating a transition from excimer emission to monomer emission of Bu-PPyV. The electron injection and EL efficiency can be fluther improved by adding small-molecule oxadiazoles into the blends as electron-transport materials. In optimized devices, an external EL quantum efficiency (backside emission only) as high as 0.8% photon/electron and practical brightnesses of 100 cd/m2 and 1000 cd/m2 can be achieved at ∼9V and ∼13.5V, respectively.

A new class of conjugated polymers have been synthesized based on the bithiazole moiety. The photoluminescence (PL) of these polymers ranges throughout the visible, from blue-green to red. These materials also show high stability, both thermal and oxidative. Therefore, it appears that this class of polymers are good candidates for polymer-based light emitting diodes.

We have prepared ZnSe nanocrystals embedded in potassium borosilicate glass matrices in concentrations up to 14 wt%. The optical and electronic properties of these nanocrystals as a function of the fabrication process were investigated with High Resolution Transmission Electron Microscopy (HRTEM) and various optical techniques including absorption, photoluminescence, and excitation spectroscopy, and photoluminescence lifetime measurements. HRTEM confirms the presence of nanocrystals and indicates an average diameter size of 50 Å. The majority of the photoluminescence extends throughout the visible and is highly red-shifted from the absorptionedge, indicating emission from trap states such as Se vacancies. Contributions from the ZnSe nanocrystals as well as the borosilicate glass matrix are also observed. Exponential and biexponential photoluminescence decays are observed with decay times ranging from a few nanoseconds to a few hundred nanoseconds. The significance of these results to the optical and electronic properties of the ZnSe nanocrystals and their relevance as luminescent materials for light emitting applications will be discussed.