白光發光二極體用具釔鋁石榴石結構螢光粉合成及其特性分析

Synthesis and Characterization of Yttrium Aluminum Garnet Phosphors for White Light Emitting Diodes

林益山(Yi-Shan Lin)

指導教授 ： 劉如熹

國立臺灣大學/理學院/化學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.02084

摘要

白光發光二極體(white light emitting diode; WLED)自1996年由日本日亞化學公司以藍光晶片為基礎搭配釔鋁石榴石(yttrium aluminum garnet; YAG)之發黃光螢光粉得白光而正式商品化至今發展近十年，期間除各式之螢光粉體與晶片之搭配組合已有廣泛之研究與報導外，白光發光二極體之應用市場亦同時有多樣之發展。此外，進一步利用紫外光二極體激發不同螢光粉之研究亦相繼展開，未來利用白光發光二極體作為人類理想之照明燈源更期望於2010年達到。
然而，綜觀目前產生白光之搭配方式上，使用兩種以上之螢光粉體於實際光能轉換效率與粉體個別劣化產生之缺點，以及使用紫外光發光二極體做為激發光源所遭遇之二極體效率之瓶頸與螢光粉體對於紫外光吸收效率低之缺點。目前最穩定之白光產生方式仍以上述之藍光晶片搭配發黃光螢光粉方式為最常見，然而欲以此結構作為照明光源，粉體之光能轉換效率及其對於激發光源之調變性仍須進一步之改善。
本研究之目的乃利用鋱離子(Tb3+)取代於釔鋁石榴石之結構，除作為一增感劑，更進一步取代釔離子(Y3+)之結構形成鋱-釔鋁石榴石之主體晶格，進而改變發光中心之發射光譜特性。此外，本研究亦於粉體合成過程利用助熔劑之添加改變晶體形成過程，進而改善鋱添加粉體其發射強渡下降之缺點，使其發光強度可優於原釔鋁石榴石，且改善後之粉體表面型態，更適合於實際發光二極體之製作。本研究亦利用真空紫外光、低溫光譜儀與固態核磁共振儀之分析，進而探討鋱-釔鋁石榴石之能量轉換與躍遷之機制。
於本研究中所使用之分析方法為以X-光粉末繞射儀(X-ray diffraction; XRD)鑑定樣品之純度及其長程有序晶體結構；利用光激發光光譜儀(photoluminescence; PL)分析螢光粉之激發光譜及放射光譜特性，並將發射光譜以程式轉換為其色度座標；利用同步輻射真空紫外光源(vacuum ultra-violet; VUV)分析螢光粉於高能量激發之發光特性與低溫光譜儀(low temperature PL)分析螢光粉於低溫下激發之放射光譜，並藉以研究其能量轉換機制；以掃瞄式電子顯微鏡(scanning electron microscope; SEM)進行樣品表面型態分析及觀察其粒徑大小之差異性；以熱重分析及差式掃描熱分析 [thermo gravimetric analysis (TGA) and differential scanning calorimetric (DSC)]分析樣品熱分解過程之重量變化及化學反應過程；以固態核磁共振儀 (solid state nuclear magnetic resonance; S. S. NMR)決定樣品中特定元素之配位環境。本研究部分成果已發表於J. Electrochem. Soc. [152, J41 (2005)]、申請四件專利及投稿三篇論文於國際期刊(Chem. Mater.；J. Electrochem. Soc.；J. Lumin.)。

關鍵字

白光發光二極體 ； 螢光粉

並列摘要

It has been about 10 years since the company of Nichia in Japan realized the white light emitting diodes (WLEDs) by combination of the blue chip with yttrium aluminum garnet (YAG) which emits yellow color. In the past years, various methods were reported in the use of different chips and phosphors and the applications of WLEDs were also noticed in various fields. At the same time, the studies of the UV-LED with phosphors were carried out. It is expected to use the WLEDs as the ideal lighting device in 2010.
Eventhough various methods have been developed over the period of time for the construction of WLEDs, there still exists some disadvantages. Firstly, preparation of LEDs by mixing more than two different phosphors results in different levels of energy transfer efficiency and decay rate for every phosphor. Secondly, the difficulties in the improvement of UV-LED efficacy still need been examined. Even now the most stable way to produce WLEDs is the combination of the blue chip and phosphors emitting yellow light as mentioned above. Nevertheless, the energy transfer efficiency and the absorbance to different excited energy of phosphors are needed to be improved in present time.
In this work, we substituted the Tb3+ into the crystal of the yttrium aluminum garnet structure and investigated its properties. Except being as sensitizers, Tb3+ ions substitute Y3+ to form the host as the terbium-yttrium aluminum garnet structure, which influenced the emission character of activators. We also introduced fluxes in the synthesis of phosphors to change crystallite-formation processes. The flux addition during synthesis enhances the emission efficiency of phosphors which is superior to commercially available phosphor. We proposed the possible mechanisms for the transition and energy-transfer process of electrons by the investigation of VUV-PL spectra, low-temperature PL spectra, and solid state NMR spectra.
In this work, we utilized X-ray diffraction (XRD) to investigate the crystal phase and long range ordering. In regard to the luminescent properties such as excitation and emission spectra, photoluminescence spectrometer (PL) was used. We also investigated luminescent properties by PL spectra excited by VUV synchrotron radiation source and the PL spectra at low temperature to study the energy transfer processes. The SEM was used to analysis the particle size and morphology of phosphors. The TGA/DSC analyses were performed to examine the weight lost process and chemical reactions during the heat treatment. We also utilized the SS.-NMR to investigate the coordination environments of critical elements. Some results of this study are already published in J. Electrochem. Soc. [152, J41 (2005)]. Three more manuscripts are under preparation (Chem. Mater.; J. Electrochem. Soc.; J. Lumin.) and four patents have been filed from the outcome of results.

並列關鍵字

WLED ； phosphor ； YAG

參考文獻

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