Korean Journal of Materials Research, Vol.21, No.5, 250-254, May, 2011
백색 LED용 청록색 BaSi2O2N2:Eu2+ 형광체의 합성 및 응용
Synthesis and Application of Bluish-Green BaSi2O2N2:Eu2+ Phosphor for White LEDs
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We have synthesized bluish-green, highly-efficient BaSi2O2N2:Eu2+ and (Ba,Sr)Si2O2N2:Eu2+ phosphors through a conventional solid state reaction method using metal carbonate, Si3N4, and Eu2O3 as raw materials. The X-ray diffraction (XRD) pattern of these phosphors revealed that a BaSi2O2N2 single phase was obtained. The excitation and emission spectra showed typical broadband excitation and emission resulting from the 5d to 4f transition of Eu2+. These phosphors absorb blue light at around 450 nm and emit bluish-green luminescence, with a peak wavelength at around 495 nm. From the results of an experiment involving Eu concentration quenching, the relative PL intensity was reduced dramatically for Eu = 0.033. A small substitution of Sr in place of Ba increased the relative emission intensity of the phosphor. We prepared several white LEDs through a combination of BaSi2O2N2:Eu2+, YAG:Ce3+, and silicone resin with a blue InGaN-based LED. In the case of only the YAG:Ce3+-converted LED, the color rendering index was 73.4 and the efficiency was 127 lm/W. In contrast, in the YAG:Ce3+ and BaSi2O2N2:Eu2+-converted LED, two distinct emission bands from InGaN (450 nm) and the two phosphors (475-750 nm) are observed, and combine to give a spectrum that appears white to the naked eye. The range of the color rendering index and the efficiency were 79.7-81.2 and 117-128 lm/W, respectively. The increased values of the color rendering index indicate that the two phosphor-converted LEDs have improved bluish-green emission compared to the YAG:Ce-converted LED. As such, the BaSi2O2N2:Eu2+ phosphor is applicable to white high-rendered LEDs for solid state lighting.
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