Synthesis and Investigation of Oxynitride Phosphors for Light Emitting Diodes
| Autor: | Yu-Huan Liu, 劉宇桓 |
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| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 Compared to conventional incandescent and fluorescent lamps, the advantages of light-emitting diodes (LEDs)-based white light sources are longer lifetime, higher efficiency, and better reliability, which promise significant reductions in power consumption and in pollution from fossil fuel power plants. The first white LED, commercialized in 1996, is composed of a blue LED and a yellow phosphor layer, namely, yttrium aluminum garnet (YAG). White light is generated from the combination of blue and yellow light produced by blue light emitting diode and yttrium aluminum garnet phosphor layer, respectively. The color rendering index (Ra) of the YAG-based LED is about 80, which is enough for general illumination. However, it is not suitable for certain medical applications and architectural lighting purposes due to the poor performance of red component in the spectra. Also the YAG phosphor has the disadvantage of thermal quenching at high temperature. In this study, we concentrate on MSi2N2O2 (M = Ca, Sr, and Ba) and Ca-α-SiAlON phosphors among the oxynitride compounds, which are nontoxic and stable under high temperature. Different luminescent properties are available by doping different activators, such as Eu, Ce, and Yb. In the yellow-greenish phosphor SrSi2N2O2:Eu, introducing Ce, Dy, or Mn ions into lattice as sensitizer could improve the emission intensity. Also, better emission efficiency is observed if the flux is involved in the reaction. Flux is used to provide a molten matrix during the diffusion controlled solid state reaction. In the system of Ca-α-SiAlON:Eu phosphor, the best ratio of Eu to Ca and influence of oxygen on nitridation synthesis are also investigated. In this work, we used X-ray diffraction (XRD) to study the crystal structure. UV-visible diffuse reflectance was used to show the absorption properties of phosphors. Besides, photoluminescence (PL) and the CIE chromaticity coordinates were obtained to show emission properties. Low temperature photoluminescence and thermoluminescence (TL) were used to study the possible energy transfer mechanism. Particle size and morphology of phosphors were investigated by SEM. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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