發光二極體激發之氧氮化合物螢光粉合成與其特性研究

Synthesis and Investigation of Oxynitride Phosphors for Light Emitting Diodes

劉宇桓(Yu-Huan Liu)

指導教授 ： 劉如熹

國立臺灣大學/理學院/化學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01443

摘要

發展高效率之綠色能源已成為各國研究團隊努力目標之ㄧ，1996年日本日亞化學公司以藍光晶片(InGaN)搭配黃色釔鋁石榴石(yttrium aluminum garnet, YAG)螢光粉而發展白光發光二極體(white light emitting diode, WLED)，開啟LED邁入照明市場之序幕。LED之體積小、發熱量低、耗電量低、壽命長、反應速度快、環保、可平面封裝易開發成輕薄短小產品等優點，無白熾燈泡高耗電、易碎與日光燈廢棄物含汞污染等缺點，目前於市面上已有多樣之應用。而據統計，若將台灣25%白熾燈泡與100%日光燈被白光LED取代，每年可省下110億度電力，大約為一座核能發電廠之年發電量。

傳統利用YAG螢光粉搭配藍光LED晶片形成白光，因其所發出之色溫高且演色性差，如歐美等寒帶地區，較不被青睞；而氧化物螢光材料於高溫下熱衰竭缺點也成為極力改善之部分。本研究提出以氧氮化合物為主體結構之綠色螢光粉(MSi2N2O2)與橘黃光(Ca-α-SiAlON)螢光材料。此氧氮化合物因具較純氧化物強之共價性，故於高溫穩定性較佳，且可適用於藍光與紫外光LED晶片，於未來之發展應用更具多樣性。

本研究目的乃於MSi2N2O2系列中添加不同之稀土元素Eu、Ce與Yb於主體晶格內，藉以改變其發光中心，進而探討其放光性質。並同時添加兩種之稀土元素Eu與Ce、 Eu與Dy、Eu與Mn，可有效提升其發光效率，並提出可能之反應機制；加入助熔劑，其可於高溫燒結時提供熔融態之環境，此將有助於反應物離子間之擴散，以利產物之晶化。於Ca-α-SiAlON系列中探討Eu(發光中心)與Ca之最佳配比與製程中氧對氮化之影響。

於本研究中以X-光粉末繞射儀(X-ray diffraction, XRD)鑑定樣品之純度與其長程有序晶體結構；以紫外可見光擴散式反射光譜(UV-vis. diffuse reflectance spectra, UV-vis. DRS)分析固態螢光粉末於紫外光與可見光其吸收特性；利用光激發光光譜儀(photoluminescence, PL)分析螢光粉之激發光譜與放射光譜特性，並將發射光譜以程式轉換為其色度座標；以掃瞄式電子顯微鏡(scanning electron microscope, SEM)進行樣品表面型態分析與觀察其粒徑大小之差異性；以低溫PL與熱螢光(thermoluminescence, TL)分析放光性質與提出可能機制。本研究部分結果已申請兩件專利。

關鍵字

發光二極體 ； 螢光粉 ； 氧氮化合物 ； 螢光 ； 氣壓燒結

並列摘要

Compared to conventional incandescent and fluorescent lamps, the advantages of light-emitting diodes (LEDs)-based white light sources are longer lifetime, higher efficiency, and better reliability, which promise significant reductions in power consumption and in pollution from fossil fuel power plants. The first white LED, commercialized in 1996, is composed of a blue LED and a yellow phosphor layer, namely, yttrium aluminum garnet (YAG). White light is generated from the combination of blue and yellow light produced by blue light emitting diode and yttrium aluminum garnet phosphor layer, respectively. The color rendering index (Ra) of the YAG-based LED is about 80, which is enough for general illumination. However, it is not suitable for certain medical applications and architectural lighting purposes due to the poor performance of red component in the spectra. Also the YAG phosphor has the disadvantage of thermal quenching at high temperature.

In this study, we concentrate on MSi2N2O2 (M = Ca, Sr, and Ba) and Ca-α-SiAlON phosphors among the oxynitride compounds, which are nontoxic and stable under high temperature. Different luminescent properties are available by doping different activators, such as Eu, Ce, and Yb. In the yellow-greenish phosphor SrSi2N2O2:Eu, introducing Ce, Dy, or Mn ions into lattice as sensitizer could improve the emission intensity. Also, better emission efficiency is observed if the flux is involved in the reaction. Flux is used to provide a molten matrix during the diffusion controlled solid state reaction. In the system of Ca-α-SiAlON:Eu phosphor, the best ratio of Eu to Ca and influence of oxygen on nitridation synthesis are also investigated.

In this work, we used X-ray diffraction (XRD) to study the crystal structure. UV-visible diffuse reflectance was used to show the absorption properties of phosphors. Besides, photoluminescence (PL) and the CIE chromaticity coordinates were obtained to show emission properties. Low temperature photoluminescence and thermoluminescence (TL) were used to study the possible energy transfer mechanism. Particle size and morphology of phosphors were investigated by SEM.

並列關鍵字

Oxynitride ； Nitride ； phosphor ； PL ； TL ； Flux

參考文獻

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