7月O/LED產業觀察(O/LED Observer Monthly JUL09, March to Lighting) -- 進入照明業
2009JUL23 LED將黃光能隙填平:使用新的氮化物磷光體可以將藍光完全的轉換成琥珀色(黃)光
(本文翻譯自Physorg.com , 圖片取自Psyorg.com)
將氮化磷光體以高密度的陶瓷發光體方式，塗佈在高效率的藍光InGaN二極體上，能在590nm波長發出最高亮度的光，並且可以將藍光完全轉換。這樣的技術，可以達到32%的外部光子效率(以每個電子發出黃光光子來計算)，這比常見的效率最佳的AlGaInP四元LED改善了300%。
在可見光波長範圍內，具有單一波長的LED通常具有較高的發光效率。以藍光來說氮化二極體可以達到65%的外部量子效率，也就是說發出的光子量大概是注入二極體中電子:電洞組合的三分之二而已。紅光二極體約可達到50%，然而到目前為止，在接近560nm黃光能隙附近，並沒有高效率的單一波長LED。目前Lumileds的研究員，開發了一種單一波長的氮化二極體，突破了這個障礙。
Regina Mueller-Mach與她的同事展示了一種利用磷光體轉換的黃光LED，她們利用磷光體將光波能量採頻率下反轉(down conversion)的方式，把InGaN LED的藍光轉換成較長波長的光，這原是廣為接受的方法，可以從藍光LED用以產製適合各種應用的冷白光或暖白光。
四年以前，Philips Lumileds研究員已經開始產製暖白光的LED。他們使用一種參雜銪的鋇鍶氮化磷光體(europium-doped barium strontium nitride phosphor)，進行頻率下反轉，她們發現藉由調整 Ba(鋇)/Sr(鍶)的比例與銪的參雜集中度，可以產生各式的光波波長，所以由原始LED發出來的光波波長，並不重要。
目前研究人員成功的將藍光波長頻率下反轉成單一波長595nm的黃光，色彩的純度高達98.7%。以磷光體轉換出來的黃光，依據操作溫度的不同，外部光子效率約30-40%，與直接發出光的黃光LED相比較，以磷光體轉換的黃光LED約有5倍的亮度，在350mA的電流下，光通量可以到達70lm。
這種新的磷光體是以多晶陶瓷的方式生產的，這種發光的陶瓷粉非常有效率的吸收藍光，另外一個優點是他的光學效能，幾乎不被溫度所影像。根據量測的結果，顏色的穩定性相比於驅動電流與溫度，也是非常的棒。
目前這些LUXEON Rebel PC黃光LED有廣泛的應用。它可用在黃色交通號誌燈，也能用在汽車的方向燈或工地的警示號誌。也可以用在消費電子商品中，它的高效能使得這些應用可以比較划算。
黃光障礙將成為過去的歷史了。
以下是Philips Lumileds的新聞稿。
SAN JOSE, Calif., Jul 01, 2009 (BUSINESS WIRE) -- Philips Lumileds today announced immediate availability of its breakthrough LUXEON Rebel phosphor converted amber (PC Amber) LED. The new LUXEON Rebel sets performance standards for color stability and light output performance. Users will see 2-5 times more light output and dramatically less color shift compared to typical amber LEDs. LUXEON Rebel PC Amber delivers typical flux of 70 lumens at 350mA. This performance enables solution and application providers to reduce the number of LEDs used, the cost per lumen, overall system costs, and simplify the solution manufacturing process.
"The number and breadth of applications that require amber LEDs is tremendous," said Frank Harder, VP of Product Marketing at Philips Lumileds. "Markets including automotive, entertainment, roadway, signaling, and many others use amber LEDs. With better efficiency and more light output, LUXEON Rebel PC Amber makes it that much easier to reduce energy consumption with an environmentally friendly product."
There are many applications that have not switched from conventional incandescent lamps to LEDs because they didn't produce enough light and couldn't operate effectively at higher temperatures. With the advances provided by LUXEON Rebel PC Amber, yellow traffic signals will be converted, warning lights and beacons on vehicles and obstructions will switch and entertainment applications will adopt the new LEDs.
Automotive applications, such as those for braking and signaling, use significant numbers of amber LEDs. With LUXEON Rebel PC Amber, manufacturers will be able to use fewer LEDs and lower other component costs because of the improved light output and particularly the stable color over temperature, something that has been problematic for many auto manufacturers. Philips Lumileds expects full automotive qualification later this year.
國內篇
2009JUL21 以電壓調節得到不同陽光色調的OLED燈
(本文翻譯自electronicsweekly.com , 圖片取自electronicsweekly.com)
台灣的研究人員已經製作出一種OLED的結構，只要更改端點的電壓就可以發出各種色調的太陽光。這種發光體是幾層的紅/橘光(590 nm)、綠光(495nm) 與藍光(460nm)的OLED材料。
根據清華大學周卓輝的說法，電洞在篩選過的材料中移動得比較快，在沒有電洞調節層的情況下，電洞幾乎會一路不停的到達紅色OLED層，與電子通透層緩慢移動出來的電子結合產生紅光。然而，周教授的電洞調節層，限制了通過紅色層的電洞數目，固定了紅光最大的強度，結果多餘的電洞，集中在綠光與藍光層，與可以輕易通過電洞調節層的電子結合，發出綠、藍光。增加端點的電壓，便可以增加藍光與綠光的發光量，然而紅光卻是固定的。
藉由縝密的選擇調節層的厚度，周卓輝得到了可以達成CIE彩色圖所定義的白光色調。輸入小於3伏特的電壓，色溫為日落的2500K，在5.5V時則是正午的5500色溫，一值增加到7V可以得到高緯度正午的色溫8000K。亮度也隨著電壓的增高，從100到1000 cd/m2，而發光效率則由7.0 lm/W到2.2 lm/W。
周卓輝預測發光效率仍可以改善，他告訴 Electronics Weekly目前使用的都是螢光體的OLED材料，磷光發光體材料可以產生更高的發光效率。
這個裝置的工作色溫，可以在製造的時候藉由不同的紅色螢光體的數量來達成，目前實作的色溫可以低點從1875~6030K，至高點3100~18800K。
OLED因很難保持適用的狀態而惡名昭彰，周教授是否發現可以了讓這個裝置成為長壽材料的改進方法呢?他回答，OLED材料只要有完善的封裝就可以輕易的達到長壽的效果了。
完整的細節，可以進一步在Applied Physics Letters (Vol.95, Issue 1)獲得。
小評
交通大學有一個307類比IC實驗室，創造出產業的傳奇。在未來照明產業進行革命性進步的時候，會不會另外創造另外一個清華大學的OLED實驗室傳奇，10年後，這個部落格存在的話，再來看看。
以下另外附上，GLG Analyst Munisamy Anandan 的評論。在文中評論，OLED 可以與CFL照明競爭的條件為：
- OLED 的發光效率可以達到80 lm/W
- 壽命可以達到 50K 小時
- 並且在 10K -20K nits 的亮度下有 10K 小時的壽命。
OLED lighting travels faster than OLED display
July 29, 2009
* Analysis by: Munisamy Anandan
* Analysis of: Konica Minolta launches OLED lighting campaign
* Published at: www.oled-info.com
Summary
1. OLED for lighting application was hitherto in R&D mode.
2. With the introduction of ' Lumiblade Experience kit' (OLED lamp)' online by Phillips for purchase and Konica Minolta's joint work with UDC and GE , the OLED technology for lighting is heating up.
3.There are still technical barriers to be crossed before OLED can compete with LED lighting.
Learn what Gerson Lehrman Group can do for you.
Analysis
Four years ago When LED lighting was gaining popularity as the next generation of lighting technology, OLED lighting came in as an R&D entrant. Since then the pace with which OLED was progressing is impressive. Many companies like Phillips, Osram, UDC, Kodak, CDT and GE were working on OLED for illumination application. Phillips has recently put on OLED lamp as 'Lumiblade Experience kit' online. GE has demonstrated a roll-to-roll manufacturing of flexible OLED lamps which is a major milestone in the area of cost of manufacturing. Unlike LED light source, OLED light source is inherently a flat light source and additionally OLED lamp has the unique advantage of being flexible. This feature is rare to find in lighting technology. 'Bendable OLED lamps' have also been demonstrated. OLED lamps with efficacy of 100 lm/w have been demonstrated in the family of phosphorescent OLED. Konica Minolta has demonstrated 64 lm/w one year ago exploiting phosphorescent technology. Konica Minolta is following up on OLED lamp technology in a significant way by jointly working with GE and UDC. There are some hurdles to be crossed by OLED technology for application in general illumination. For example CFL yields a luminance of 10,000 nits to 20,000 nits with an efficacy of 70-80 lm/w. The question to be answered by OLED technology is whether OLED can attain 80 lm/w at these luminance levels and if so whether the life performance will be 50K hours (comparing with LED) at these luminance levels or 10K hours comparing with CFL.
The companies like UDC, GE, Phillips, Osram, Konica Minolta, CDT, Kodak, Idemitsu Kosan may be working on to enhance the reliability of OLED at high luminance encountered in lighting. Already work on 'Tandem hybrid white OLED' has commenced and this approach is likely to be the key.
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