Synthesizing Phosphors Through Microwave Process
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0988-QQ06-20
Synthesizing Phosphors Through Microwave Process Chris Y. Fang1, Dinesh K. Agrawal1, Ming Fu1, Joan M. Coveleskie2, Chung-nin Chau2, James Walck2, and Rustum Roy1 1 Materials Research Institute, The Pennsylvania State University, University Park, PA, 16802 2 OSRAM SYLVANIA, Inc., Hawes Street, Towanda, PA, 18848
ABSTRACT Various Lamp phosphors, including [Ca10(PO4)6(Cl,F):Sb:Mn], (Y,Eu)2O3 (YOE), BaMgAl10O17:Eu (BAM), and (La,Ce)PO4:Ce:Tb (LAP), with or without flux, have been synthesized by a microwave processing technique in a multimode microwave furnace operating at 2.45 GHz. The microwave-synthesized phosphors were comprehensively characterized for particle size, specific surface area, brightness, and luminescence. Although most properties of the microwave-synthesized phosphors were comparable to that of the conventional products, the kinetics of the phosphor synthesis was substantially enhanced in the microwave processing. As a result, the soaking time at the final temperature was reduced by up to 90% compared to a conventional process. In addition, the required synthesis temperature was also lowered by 100200°C in microwave process, compared to the conventional process for these lamp phosphors. Certain improved property was also observed in some microwave synthesized samples. The mechanism and advantages of microwave process for the lamp phosphor synthesis through solidstate reaction are addressed.
INTRODUCTION In order for the activators to be incorporated into the crystal lattice structure of the host material, a high temperature thermal treatment is necessary in the synthesis of lamp phosphors. Conventional processing of fluorescent lamp phosphors includes blending of the starting materials, loading the mixtures into crucibles, and firing at a high temperature for several hours. Additional finishing steps may include milling, washing to remove inert materials, filtering, drying, and blending. The total firing process may take 8-12 hours. In order to lower the firing temperature and accelerate the synthesis, flux is normally used. The conventional process of phosphor synthesis is not only complex, but also requires significant time and energy. Further, contamination due to the volatiles from the process has been a concern. Microwave processing of ceramic materials is referred to Sutton [1]. Research on microwave processing of materials has been active in the Materials Research Institute at the Pennsylvania State University since early 1980’s [2-8]. Microwave processing of various materials including ceramics, composites, cermets, hard metals, electronic ceramics, metallic materials, etc. have been investigated in this laboratory with success.
The general features of microwave processing of materials include volumetric and selective heating, enhanced kinetics, the potential to improve product quality, process simplification, and the potential of cost reduction. Generally, microwave processing of ceramic materials is a dielectric heating process. The mechanism of microwave heating is inherent
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