Sol-gel Synthesis and Characterization of YAG:Ce 3+ Phosphors by Various Pre-firing Temperatures
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1148-PP03-22
Sol-gel Synthesis and Characterization of YAG:Ce3+ Phosphors by Various Pre-firing Temperatures Kyu-Seog Hwang1, Seung Hwangbo2, Ju-Hyun Jeong3, Young Hwan Lee4 and Jin-Tae Kim5 Department of Biomedical Engineering and Institute of Photoelectronic Technology, Nambu University, Gwangju 506-824, Korea 2 Major in Photonic Engineering, Division of Electronic & Photonic Engineering, Honam University, Gwangju 506-714, Korea 3 Department of Ophthalmic Optics, Konyang University, Daejeon 302-718, Korea 4 Department of Automobile, Chunnam Techno College, Jellanam-do 516-911, Korea 5 Department of Photonic Engineering, Chosun University, Gwangju 501-759, Korea 1
ABSTRACT Ceria doped-yttrium aluminum garnet (Y3Al5O12:Ce3+, YAG:Ce), which is known as an efficient phosphor, have been widely used in optical display and lighting applications. Improved wet chemical method, sol-gel, has been studied, since conventional solid-state reaction requires a high-temperature and prolonged heating to obtain the pure phase. However, there has been little information, such as on pre-firing temperature, concerning high-quality powder formed by the wet chemical process. In this work, YAG:Ce was synthesized with a salted sol-gel process in which a water solution of inorganic salt with citric acid as additive. Transparent starting sol was pre-fired at 200 ~ 300°C for 2 hrs in air and final annealing to obtain phase-pure YAG:Ce particles was performed at 1100°C for 2 hrs in argon. The effects of pre-firing temperatures on the crystal structure, morphology and luminescence were investigated. Effects of residual organics in the pre-fired gel on the properties of finally annealed phosphors will be fully discussed on the basis of the results of thermal analysis and chemical structure. INTRODUCTION Tuning of light emitting diode (LED) monochromatic emission to various colors including realization of white light is possible by using phosphors which emit blue, green, yellow and red wavelengths simultaneously. Recently, lot of yellow color phosphors are used for the conversion of blue emission from blue LED into white light emitting LED. YAG:Ce is a known phosphor showing an efficient long-wavelength, broad luminescence located around 530~540 nm [1]. The resulting mixture of blue LED and yellow YAG:Ce gives the appearance of white light [2]. Due to the special electronic structure of rare earth ions where the electrons on its 5d orbits are in an exposure condition without shielding, these electrons make a transition from 5d to 4f on the effect of external factors, and consequently activate the YAG. Traditionally, phosphors are prepared by solid-state reactions at temperatures above 1600°C. Due to insufficient mixing and the low reactivity of raw materials, several intermediate phases such as Y4Al2O9 (YAM) and YAlO3 (YAP) easily exist in the products [3]. In order to overcome the drawbacks of the solid-state reaction process, improved wet chemical techniques, such as co-precipitation [4], combustion [5], and sol-gel [6] have been developed. R
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