저온 플라즈마 방전 하에서의 Sr2SiO4:Eu2+ 형광체의 합성

Abstract

A blue LED chip and Y3Al5O12:Ce (YAG:Ce) phosphor are currently used for the White LED manufacturing. YAG:Ce phosphor is synthesized in a difficult way but have high photoluminescence intensity and good stability. However, this phosphor is protected by the patent of Nichia (Japan). Silicate-based phosphors are being developed to replace YAG:Ce phosphor. It has lower luminescent intensity, reliability than YAG:Ce, while is easily manufacture. Also, it can be implemented in a variety of colors because controlling the emission spectra can be possible with simple changes of the composition in materials. The synthesis of Sr2SiO4:Eu2+ phosphor and surface treatments discussed in this research. Sr2SiO4:Eu2+ phosphors are conventionally synthesized at high temperature which necessarily requires the intensive energy use, leading to high operational cost. As well, treatment time of the conventional method is rather long, which decreases productivity. An attempt has been made to apply nonthermal plasma discharge to the preparation of Sr2SiO4:Eu2+ phosphor. Some variables such as sintering temperature, treatment time and discharge voltage were changed to investigate their effects of plasma discharge on the properties of the phosphor synthesized. The surface morphology was observed by a field emission scanning electron microscope and the crystalline structures of the synthesized phosphor were investigated with X-ray diffraction analyzer. The luminous characteristics of the materials were analyzed by a fluorescence spectrophotometer. As a result, synthesized phosphor with applying discharge in the equal condition have higher photoluminescence than the phosphor without applying voltage. Also, this research way can decrease the temperature and the treatment time in the conventional synthesis method. In order to cope with the low reliability to the temperature and humidity of the phosphor, the hydrophobic treatments on the surface of the phosphor were carried out in the high temperature and humidity condition. The hydrophobicity of the phosphor was measured using contact angle analyzer, the changes on the surface was analyzed using FTIR and the emission spectra were taken to analyze the alternations in the luminescence characteristics. Also the morphology of the surface was observed with a transmission electron microscope and a FE-SEM. And the phosphor-loaded LED chips were maintained for some time with high temperature and high humidity condition (85oC and 85 RH%). Consequently, the hydrophobic film with a size of about 50 nm was formed on the surface of the particle. The overall treated phosphor had high photoluminescence in the high temperature and high humidity condition, and did not show the sharp decline of the luminescence.