發光二極體之螢光材料及其封裝特性分析
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2008
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原油價格於2008年六月份創下每桶140美元歷史新高價位，年初至今原油價格已飆漲40%，與去年同一時期相比正好整整漲了一倍。科學家並預期2008年夏天於溫室效應持續急遽惡化下，北極冰層有50%機率會全部融化流入大海，迫使低海拔城市面臨被淹沒之危機。於此，開發新型替代性能源與如何有效節約能源消耗是當今重要之研究課題，但當前替代性能源無法被有效地被利用來取代石油，故如何節約能源則成為最迫切之問題。固態照明，即為一有效之解決方案，如全中國大陸能以LED取代目前之照明設備，將省下一座三峽大壩全年之發電量。本文所探討之發光二極體於此照明革命中扮演著舉足輕重之角色。
1996年日亞化學Nakamura等人成功成長藍光發光二極體，並搭配黃色摻鈰之釔鋁石榴石(cerium doped yttrium aluminum garnet, YAG:Ce)，成功發展白光LED。近年來於白光LED之發展日新月異，藍光晶片搭配YAG雖發光效率佳，但仍有藍光轉換效率不佳以及其白光演色性不高之問題。為規避日亞YAG專利之問題，矽酸鹽類發展亦受到重視，其發光效率與YAG屬伯仲之間，但近來研究發現其熱穩定性與抗濕性不佳。故本研究著重於UV激發之高色純度螢光粉，本研究發現鉀鍶磷酸鹽(KSrPO4)之熱穩定性及抗濕性佳，分別摻雜二價銪(Eu2+)及三價銪(Eu3+)產生藍光與紅光。再者，發現摻雜Eu2+之氯鋁酸鍶(Sr3(Al2O5)Cl2)光譜較YAG紅位移且半高寬大，故可解決演色性不高之問題。針對以上三種螢光粉進行材料結構、光譜特性與可靠度三大類之分析。
本研究之KSrPO4:Eu2+部分內容已發表於Appl. Phys. Lett. 90, 151108 (2007)，研究其熱穩定性。Sr3(Al2O5)Cl2:Eu2+乃一新穎之螢光粉，並未有相關文獻報導，日前已提出專利申請。
The development of blue light-emitting diodes (LEDs) is hindered mainly due to the difficulties in the processing. After the initial discovery of white light generation by using GaN based LEDs in combination with a yellow phosphor (cerium doped yttrium aluminum garnet, YAG:Ce) by Nakamura et al. of Nichia, a great progress has been achieved in the development of white LEDs. The light emitting diodes has several advantages over the conventional light sources such as energy saving, eco friendly characteristics and so on. Due to the arising eco-awareness, various nations target to achieve the goal of “Kyoto Protocol” of decreasing the levels of carbon dioxide in next 3～4 years. However, the above mentioned strategy of white light generation faces serious problems such as low conversion efficiency of blue LED and poor color rendering index. In this regard, silicate based phosphors have attracted much attention due to its superior luminescence properties in comparison with YAG. However the silicate based phosphors are also found to be thermally unstable. The present work is focused on near UV excitable phosphate based phosphors exhibiting high color saturation properties. We have observed that the luminescence of Eu2+ doped KSrPO4 is thermally more stable than YAG phosphor and not sensitive to moisture. The studies on Sr3(Al2O5)Cl2 doped with Eu2 were also performed which showed the peak broadening as well as red shift of the spectrum (PL) as compared to YAG. This provides the solution for problem of low color rendering index. The phosphor materials were characterized by various techniques such as X- ray diffraction analysis (XRD), scanning electron microscopy (SEM), photoluminescence (PL) measurements etc. A part of the present studies related to the KSrPO4 phosphor and its thermal stability has been published in the journal, Appl. Phys. Lett. 90, 151108 (2007) and we have also filed a patent on UV excitable Sr3(Al2O5)Cl2:Eu2+ phosphors for application in LEDs.
The development of blue light-emitting diodes (LEDs) is hindered mainly due to the difficulties in the processing. After the initial discovery of white light generation by using GaN based LEDs in combination with a yellow phosphor (cerium doped yttrium aluminum garnet, YAG:Ce) by Nakamura et al. of Nichia, a great progress has been achieved in the development of white LEDs. The light emitting diodes has several advantages over the conventional light sources such as energy saving, eco friendly characteristics and so on. Due to the arising eco-awareness, various nations target to achieve the goal of “Kyoto Protocol” of decreasing the levels of carbon dioxide in next 3～4 years. However, the above mentioned strategy of white light generation faces serious problems such as low conversion efficiency of blue LED and poor color rendering index. In this regard, silicate based phosphors have attracted much attention due to its superior luminescence properties in comparison with YAG. However the silicate based phosphors are also found to be thermally unstable. The present work is focused on near UV excitable phosphate based phosphors exhibiting high color saturation properties. We have observed that the luminescence of Eu2+ doped KSrPO4 is thermally more stable than YAG phosphor and not sensitive to moisture. The studies on Sr3(Al2O5)Cl2 doped with Eu2 were also performed which showed the peak broadening as well as red shift of the spectrum (PL) as compared to YAG. This provides the solution for problem of low color rendering index. The phosphor materials were characterized by various techniques such as X- ray diffraction analysis (XRD), scanning electron microscopy (SEM), photoluminescence (PL) measurements etc. A part of the present studies related to the KSrPO4 phosphor and its thermal stability has been published in the journal, Appl. Phys. Lett. 90, 151108 (2007) and we have also filed a patent on UV excitable Sr3(Al2O5)Cl2:Eu2+ phosphors for application in LEDs.
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Keywords
發光二極體, 螢光粉, LED封裝, Light emitting diodes, phosphor, LED package