Epitaxial Oxide Thin-Film Phosphors for Low Voltage FED Applications
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Epitaxial Oxide Thin-Film Phosphors for Low Voltage FED Applications Yong Eui Lee, David P. Norton, John D. Budai, Philip D. Rack1, Jeffrey Peterson1, and Michael D. Potter1 Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6056 1 Advanced Vision Technologies, Inc., W. Henrietta, New York 14586 ABSTRACT Epitaxial ZnGa2O4 and Sr2CeO4 thin-film phosphors were successfully grown on (100) MgO, YSZ, and SrTiO3 single crystal substrates using pulsed laser ablation. Cathodoluminescence efficiency was remarkably enhanced by adding lithium in the ZnGa2O4 and ZnGa2O4:Mn for both blue and green light emitting thin-film phosphors. The highest efficiencies, in this experiment, were 0.35 and 0.29 lm/W at 1kV for as-deposited blue and green zinc gallate phosphor films, respectively. In case of Sr2CeO4 films, the highest luminescence was 0.14 lm/W at 1kV and 0.26 A/m2 for films annealed at 1000oC in air. INTRODUCTION Oxide thin-film phosphors are very attractive for field emission displays (FEDs) which operated with low voltage and high current density. Advantages include high resolution screens, enhanced lifetime at high current density, and excellent thermal and mechanical stabilities. Unfortunately, one of the fundamental problems for oxide thin-film phosphors in applications is inferior luminous efficiency and brightness as compared to powder systems. Many researchers have studied luminescence for thin-film phosphors in an attempt to improve the properties through increasing light scattering centers using surface modification, reducing defect density by post-annealing at high temperatures, and identifying new phosphor materials.[1-3] Recently, Lee et al.[4] reported that epitaxial phosphor films exhibit superior photoluminescent (PL) intensity as compared to randomly-oriented polycrystalline films on glass substrates. This result indicates enhanced luminescence due to improved intragranular crystallinity via epitaxy. The study of epitaxial phosphor film is useful not only for achieving high luminescence performance, but also in understanding the fundamental properties of the materials. Most known phosphor materials are multi-component materials possessing complex crystallographic structures, making it difficult to find suitable deposition technique and/or substrate materials for epitaxial film growth. Recently several interesting studies on low-voltage blue and/or green light emitting cathololuminescent(CL) oxide phosphors have been reported. 1. ZnGa2O4 and mixtures of Li2O/LiGa5O8 and ZnGa2O4 having a spinel crystal structure have showed improved CL properties in powders and have been suggested as promising candidates in applications of FEDs.[5-6] 2. Sr2CeO4 have showed high efficiency in CL about 5.4 lm/W at 4 kV.[7] We have investigated the growth and luminescence characteristics of several oxide thin-film phosphors including ZnGa2O4, LixZn1-xGa2O4, ZnGa2O4:Mn, LixZn1-xGa2O4:Mn, and Sr2CeO4 for blue and green low-voltage CL.
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EXPERIMENTAL DETAILS Blue light emitting LixZn1-xGa2O4(x=0-0.2), mixt
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