| Summary: | 博士 === 國立高雄第一科技大學 === 工程科技研究所 === 102 === Considering blue LEDs emit light with a wavelength is shorter than the green ones, it is possible to excite a suitable and intense yellow light-emitting phosphor which is complemented into the blue emission, and then a yield ideal white light is created. Out of all the phosphor LEDs involved, Ce doped yttrium-aluminate-garnet phosphor was found to be the most suitable satisfactorily tested on GaN LEDs for the production of white light. Recently, because of the high power LED growth, its driving current is increased, therefore heat problem is become a main issue, and will affect luminous efficiency. In order to overcome the above shortcomings, it is necessary to take a way to improve the conversion efficiency and thermal stability simultaneously. Regarding the heat problem, the phosphate oxide compound ( ABPO4，A=Li+, Na+, K+, Rb+, Cs+，B=Mg2+, Ca2+, Sr2+, Ba2+ ) as the host lattice of covalent nature of the phosphor with three dimensional rigid structure. The phosphate oxide is very suitable for carrier transport, and the thermal stability of the phosphate series is quite outstanding. Using phosphate as host lattice in the phosphor material can solve the thermal problem of the high power of white LED in effective way.
In this study, KSrPO4’s phosphate structure is selected as the host lattice and Sm is chosen as the flux. Instead of the traditional sintering method, KSrPO4:Sm3 phosphate is made by using microwave assisted sintering technique, and then the microstructure, material and photo-luminescent properties of phosphate are investigated. The experiment results show that KSrPO4:Sm3+ phosphors have a uniform particle size distribution, and the excitation and emission spectra of the KSrPO4:Sm3+ phosphors indicate that they can be effectively excited by a NUV LED chip, and emit mainly at the 599 nm red wavelength, when sintering temperatures was increased to 1200°C from 1000°C, significant change in the morphologies and increase in particle size. When the sintering temperature was increased to 1300°C, a liquid phase sintering results in abnormal grain growth.
Moreover, several fluxes were used to improve the sintering process and to enhance the photo-luminescent properties in phosphor. In this study, NH4Cl is also adopted as fluxes to synthesis KSrPO4:Sm3+ phosphors. The experiment result shows that the emission intensity of KSr0.99PO4:0.01Sm3+ phosphors with 2 wt. % NH4Cl flux is also enhanced when the sintering temperature climbed to 1150°C from 1050°C and the maximum degree is at 1150°C, but the photo-luminescent is decreased dramatically when the sintering temperature was increased to 1200°C.
In the last part of this study, the optimal parameter for phosphor of KSrPO4:Sm3+ red phosphate is chosen and packaged it into the LED. The experimental results presented that the thermal quenching temperature T50 of the prepared KSr0.99PO4:0.01Sm3+ phosphor is 300°C and the phosphor could be successfully applied in LED.
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