Photoluminescence of Nano-scaled YAG: Ce Phosphor Powders
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Photoluminescence of Nano-scaled YAG:Ce Phosphor Powders In-Gann Chen(1), Yulin Chen(1), Chii-Shyang Hwang(1), F.S. Juang(2), S.J. Chang(3), Y.K. Su(3), G.O. Mueller(4), and R. Mueller-Mach(4) (1) Department of Materials Science and Engineering, National Cheng Kung University, Tainan, TAIWAN (2) Department of Electro-Optics Engineering, National Huwei Inst. of Tech, Huwei, Yunlin, Taiwan. (3) Department of Electrical Engineer, National Cheng Kung University, Tainan, TAIWAN, (4) Lumileds Lighting, LLC, San Jose, CA, U.S.A.
ABSTRACT Four series of YAG:Ce phosphor powders were synthesized by solid state, co-precipitation, and sol-gel (with two different growth inhibitors, HMDS and PAA respectively) methods, which results in the average particle sizes of 800, 56, 43, and 32 nm respectively. All the nano-scale YAG powders were heat treated below 1000_. Both TEM and XRD results of these nano-scale YAG powders show high degree of crystalline structure. Photoluminescence (PL) characterization shows that the nano-scale YAG phosphor powders emit a higher intensity of luminescence than that of sub-micro sized samples. The effect of different Ce doping level on the PL of (Y3-xCex)Al5O12 shows a maximum at x ~ 0.01. The Commissiom International de I’Eclairage (CIE) chromaticity coordinates were determined and show different trends of shifts in the resulting PL spectra. Systematic study of the processing parameters characterized by DTA/TGA, XRD, FTIR, and BET will be discussed in detail in the report. I.
INTRODUCTION
Yttrium garnet (Y3Al5O12, YAG) has been known to be an optoelectronic material for solid state lasers, e.g. YAG:Tb can be used for blue-green light laser. Since recently, it is also known that it can be used as white light phosphor materials if integrated with the GaN blue light emitting diode (LED). Traditionally, the YAG powders are synthesized by solid-state calcinating Y2O3 and Al2O3 with a 3:5 stoichiometrical ratio at ~1700 _. Flux materials, such as BaF2, are frequently used to reduce the calcinating temperature. Since the relatively high processing temperature, the size of the YAG powder synthesized by solid-state method is in the 10 µm range. The phosphor powder is utilized as an energy transfer medium, which absorbs high frequency electromagnetic wave and emits lower frequency electromagnetic waves. It is believed that a higher surface to volume ratio (i.e. a smaller particle size) will enhance the efficiency of absorption and emission of electromagnetic waves. In this report, we have prepared nano to micro scale YAG powders with four different methods and compare their photoluminescence (PL) properties.
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EXPERIMENTAL PROCEDURE
Four series of YAG:Ce phosphor powders were synthesized by solid state, co-precipitation, and sol-gel methods (with two different
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