Papers

AVS1996 Session FP-ThA: Luminescent Materials

Thursday, October 17, 1996 1:30 PM in Room 204B

Thursday Afternoon

Start	Invited?	Item
1:30 PM		FP-ThA-1 Pulsed Laser Deposition of Tb-doped Y\sub 2\O\sub 3\ Photoluminescent Thin Films J. Alonso, E. Haro-Poniatowski, R. Diamant, M. Fernandez-Guasti (Universidad Autonoma Metropolitana Iztapalapa, Mexico); M. Garcia (UNAM, Mexico) We have deposited Tb-doped Y\sub 2\O\sub 3\ luminescent thin films by pulsed laser ablation of a sintered target, using the fundamental frequency (1064 nm)of a Nd:YAG laser. Films deposition was performed, either in vacuum or in an oxygen atmosphere, on corning glass and silicon substrates at temperatures between ambient and 250 \super o\C. It was found that the oxygen pressure during deposition plays a determinant role on the luminescent and structural properties of the films. Independently of substrate temperature, all films deposited at the highest oxygen pressure (3 X 10 \super -4\ Torr), are polycrystalline and their photoluminescence spectra show emission lines characteristic of 4f -> 4f transitions of trivalent Tb ions. The photoluminescence efficiency and the crystallinity of these films improves slightly as the substrate temperature increases. On the other hand, the photoluminescence intensity of polycrystalline films deposited at the highest temperature strongly decreases as the oxygen pressure is decreased. X-ray diffraction, refractive index and energy dispersive spectroscopy (EDS) measurements reveal that the changes in the luminescence efficiency are associated with structural and compositional changes. A preliminary optical emission analysis of the plasma plume of the ablated material is also reported.
1:50 PM		FP-ThA-2 Electron Beam Dissociation of CO and CO\sub 2\ on ZnS Thin Film Field Emission Display Phosphors Y. Darici, S. Milano (Florida International University); J. Sebastian, T. Trottier, S. Jones, S. Sosa, P. Holloway (University of Florida, Gainesville) ZnS doped with transition or rare earth elements is a common cathodoluminescent phosphor used in CRTs and potentially in field emission flat panel displays (FEDs). However, sulfide phosphors are known to degrade with total electron dose under CRT or FED conditions which consist of a vacuum with residual gases of mainly CO and CO\sub 2\. We have measured the dissociation of these residual gas species on ZnS by backfilling a UHV chamber to pressures between 10\super -9\ and 10\super -6\ Torr and irradiating the surface with 2 keV electrons to doses of over 200 C/cm\super 2\. The CO dissociated under the electron beam leaving C on the ZnS surface, but little oxidation took place. The electron beam also cracked CO\sub 2\, which led to severe oxidation as well as limited C deposition on the surface. The effects of temperature on these reactions were studied, and at T > 300\super o\C, there was sufficient atomic mobility to replenish the S from the interior of the ZnS. The consequences of these electron beam stimulated surface reactions on the use of ZnS for FED phosphors will be discussed. @-This work supported at UF by a grant from the Phosphor Technology Center of Excellence.
2:10 PM		FP-ThA-3 High Luminance Nanophosphors by a Novel Gas Condensation Process J. Lin (Rutgers University); G. Skandan (Nanopowder Enterprises, Inc.); E. Forsythe (Structured Materials Industries, Inc.); J. Liu, D. Morton (Army Research Laboratories); B. Kear (Rutgers University) Recently, there has been much interest in the synthesis of high luminance phosphors with a particle size < 1 \mu\m. These phosphors can have immediate applications in Field Emitter Displays (FEDs), Electroluminescent (EL) displays and high resolution printing. We have synthesized blue, green and red phosphor nanoparticles by doping the host matrix (e.g. Y\sub 2\O\sub 3\ or Y\sub 2\O\sub 2\S) with rare-earth elements (e.g. Ce, Tb and Eu) in the gas phase. In certain cases, post heat treatments in a suitable atmosphere at relatively low temperature (~ 800 - 900 \super o\C) are necessary to improve the activation of the dopants. This is a consequence of the short diffusion distance in nanoparticles. Furthermore, we have added sulphur to the nanophosphors to produce Y\sub 2\O\sub 2\S which significantly increases the brightness. The particles are well below 100 nm in size as characterized by TEM and XRD, and show photoluminescence (PL) intensity comparable to commercial ! powders. Emission intensity and wavelength are reported as a function of dopant, dopant concentration and powder processing methodology. The nanophosphors have shown higher cathodoluminescence (CL) efficiencies at a low voltage (< 1000 eV) compared to conventional phosphors. The structure of these phoshpors including particle size and composition variation, along with performance evaluation such as PL, EL, and CL, will be presented.
2:30 PM		FP-ThA-4 Characterization of Novel Luminescent Films for Field Emission Flat Panel Display Application A. Chakhovskoi (University of California, Davis); M. Malinowski, T. Felter (Sandia National Laboratories); C. Hunt (University of California, Davis); J. McKittrick, G. Hirata (University of California, San Diego) The spectral response, brightness and outgassing characteristics of new, low-voltage thin film luminescent materials for application in field-emission flat-panel displays, are presented. Tested screen samples include thin films prepared by laser ablation and by chemical vapor deposition techniques. Thin films about 5000 Angstrom thick are deposited on top of ITO-coated glass or on sapphire substrates. These cathodoluminescent materials are tested with e-beam excitation at currents up to 50 microamps within the 200-2000V (eg. "low-voltage") and 3-8 kV (eg. "medium voltage") ranges. The spectral coordinates are reasonable compared to industrially manufactured low-voltage P22 powder phosphors. Output brightness is measured as a function of the acceleration voltage. Phosphor outgassing is characterized with a residual gas analyzer after preliminary thermal bakeout. The outgassing spectra and the desorption rates measured for thin films are compared to desorption from powder phosphor layers with different thicknesses, and to calculated desorbtion rates acceptable for field emission display applications.
2:50 PM		FP-ThA-5 Structural and Optical Properties of Alkali Halide Multilayers LiF:NaF Films F. Somma (Universit\ag a\ di Roma, Italy); S. Santucci, M. Passacantando (Universit\ag a\ dell'Aquila, Italy); R. Montereali (ENEA, C.R.Frascati, Italy); R. Nunes, M. Cremona (PUC University, Brazil) Alkali-Halide multilayer films containing a large concentration of colour centres created by low energy (3-30 keV) electron beams in a thin dielectric layer of controlled depth, represent a good and simple way to obtain new optical active materials. In this work we present a study on multilayer LiF:NaF films, grown by physical evaporation on glass substrates, which were coloured with low energy electrons. The characterization of the samples has been performed using the XPS depth profile for the profile composition, AFM technique for the surface morphology and optical absorption and photoemission measurements for the optical properties. Visible photoluminescence of optically active defects created by electron irradiation both in LiF and NaF layers, which constitute the film, was measured by excitation with an Ar laser. Controlling the deposition and colouration parameters it is possible to obtain photoluminescent materials with predesigned optical features.
3:10 PM		FP-ThA-6 Y\sub 2\O\sub 3\:Eu and Y\sub 3\Al\sub 5\O\sub 12\:Eu Red Luminescent Films G. Hirata (UNAM, Mexico); J. McKittrick (University of California, San Diego); M. Avalos, J. Siqueiros (UNAM, Mexico); D. Devlin (Los Alamos National Laboratory) In this work we describe the preparation and analyses of red luminescent thin films grown by metallorganic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD) on different substrates. Y\sub 2\O\sub 3\:Eu microcrystalline films were grown in a MOCVD chamber by decomposing yttrium and europium diketonates in an oxygen atmosphere. As-deposited films showed the characteristic luminescence spectrum of Y\sub 2\O\sub 3\:Eu with the main peak centered at about 611 nm wavelength (\super 5\D\sub 0\-\super 7\F\sub 2\ transition in Eu\super +3\ ion under UV excitation). Annealing treatments at relatively high temperatures (900-1400\super o\C) enhanced the photoluminescence intensity of the microcrystalline films. In this work we have also deposited Y\sub 2\O\sub 3\:Eu and Y\sub 3\Al\sub 5\O\sub 12\:Eu (YAG:Eu) red luminescent films by PLD under ultra-high vacuum conditions. Non-luminescent films were produced by this technique and post-annealing treatments were also necessary in order to recover the red luminescence on both different oxide films. Analyses by Scanning Electron Microscopy and High Resolution Transmission Electron Microscopy revealed that polycrystalline films with size particles in the range 0.5-2.0 microns were obtained by MOCVD. On the other hand, smooth films with nano-size grains were produced by laser ablation
3:30 PM		FP-ThA-7 Pulsed Laser Deposition of Thin Film Phosphors for Field Emission Flat Panel Displays S. Jones, D. Kumar, R. Singh, P. Holloway (University of Florida, Gainesville) The brightness, efficiency and lifetime of phosphors for field emission displays (FEDs) are currently limiting their commercial development. While most phosphors used have been powders, there are numerous reasons to use thin film phosphors for these devices. However, thin films suffer from low brightness and efficiency relative to powders. This results partially from poor crystallinity, stoichiometry issues, and/or multiple internal reflections of the emitted light. PLD of thin films has several potential advantages for deposition of phosphors, including evaporation of multi-component refractory materials, and variation of surface morphology to negate internal reflections. In this study, luminescent thin films of SrS:Ce and Y\sub 2\O sub\3\:Eu thin films have been deposited at varying temperatures. The SrS films grown yielded CIE coordinates of x = 0.206 and y = 0.393 and a brightness of 1.21 fL, compared to sputter deposited films. Y\sub 2\O\sub 3\:Eu films yielded CIE coordinates of x = 0.601 and y = 0.340 also with good brightness. The surface morphology has been varied, measured with SEM and AFM, and a good correlation established with brightness, Auger electron spectroscopy, secondary electron microscopy along with cathodluminescence and photoluminescence to correlate changes in structure and composition with brightness.