白光LED用Ce:YAG单晶光学性能及封装工艺的研究

引用本文

向卫东, 赵斌宇, 梁晓娟, 陈兆平, 谢翠萍, 骆乐, 张志敏, 张景峰, 钟家松. 白光LED用Ce:YAG单晶光学性能及封装工艺的研究. 无机材料学报, 2014, 29(6): 614-620
XIANG Wei-Dong, ZHAO Bin-Yu, LIANG Xiao-Juan, CHEN Zhao-Ping, XIE Cui-Ping, LUO Le, ZHANG Zhi-Min, ZHANG Jing-Feng, ZHONG Jia-Song. Packaging Technologies and Luminescence Properties of Ce:YAG Single Crystal for White Light-emitting Diode. Journal of Inorganic Materials, 2014, 29(6): 614-620 复制到剪切板

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白光LED用Ce:YAG单晶光学性能及封装工艺的研究

向卫东^1,², 赵斌宇², 梁晓娟¹, 陈兆平¹, 谢翠萍², 骆乐², 张志敏¹, 张景峰^1,², 钟家松²

1. 温州大学化学与材料工程学院, 温州 325035

2. 同济大学材料科学与工程学院, 上海 201804

作者简介: 向卫东(1962-), 男, 博士, 教授. E-mail:xiangweidong001@126.com

基金:国家自然科学基金(5117216551372172);
浙江省自然科学基金重点项目(Z4110347); 浙江省重大科技专项重大工业项目(2012C01028-2);
湖州市自然科学基金(2011YZ02);

摘要

采用提拉法生长了白光LED用Ce:YAG单晶, 通过吸收光谱、激发发射光谱和变温光谱对其光学性能和热稳定性进行了表征, 并研究了晶片用于封装白光LED光源中各因素对其光电性能的影响。Ce:YAG晶片能被466 nm波长的蓝光有效激发, 产生500~700 nm范围内的宽发射带。Ce³⁺的4f→5d轨道的跃迁吸收对应于202、219、247.3、347.4和455.5 nm五个吸收峰, 据此量化分裂的5d能级能量, 依次为21954、29154、40437、45662和49505 cm^-1。温度升高, Ce³⁺的²F_7/2能量升高导致了发光强度的降低, 可降低幅度(13.28%)不大, 比肩国家标准且要优于目前商用白光光源的Ce:YAG单晶制白光LED光源的封装工艺, 从芯片、驱动电流、晶片厚度和添加物四方面进行讨论。研究结果表明, Ce:YAG单晶是一种新型白光LED用荧光材料。

关键词: 白光LED; 铈掺杂钇铝石榴石; 光学性能; 封装工艺; 光电性能

中图分类号:O734 文献标志码:A 文章编号:1000-324X(2014)06-0614-07

Packaging Technologies and Luminescence Properties of Ce:YAG Single Crystal for White Light-emitting Diode

XIANG Wei-Dong^1,², ZHAO Bin-Yu², LIANG Xiao-Juan¹, CHEN Zhao-Ping¹, XIE Cui-Ping², LUO Le², ZHANG Zhi-Min¹, ZHANG Jing-Feng^1,², ZHONG Jia-Song²

1. College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325035, China

2. College of Materials Science and Engineering, Tongji University, Shanghai 201804, China

Fund:National Natural Science Foundation of China (5117216551372172);
Natural Science Foundation of Zhejiang Province (Z4110347);
Major Technology and Industrial Program of Zhejiang Province (2012C01028-2);
Natural Science Foundation of Huzhou (2011YZ02);

Abstract

The Ce:YAG single crystal for white light-emitting diode (WLED) application was grown by the Czochralski method. The thermal stability and optical properties of samples were characterized by absorption spectrum, photoluminescence spectra and temperature-dependent PL spectra. The photoelectric performance of WLEDs fabricated by the Ce:YAG single crystal were also measured. It is found that the Ce:YAG single crystal shows a broad emission band from 500 nm to 700 nm under blue light (wave length 466 nm). Absorption peaks, located at 202, 219, 247.3, 347.4 and 455.5 nm, are due to 4f→5d transition, and the energy of 5d orbits is divided into 21954, 29154, 40437, 45662 and 49505 cm^-1. As the temperature increases, the PL intensity is reduced because of a higher energy of the²F_7/2, and the damping upon PL intensity by the Ce:YAG single crystal (13.28%) are much lower than that by commercially available phosphors (30%). When the current is at a standard state and the luminous flux of emission blue light is around 3.7 lm, the most suitable thickness for the Ce:YAG single crystal is 0.5 mm. Since the WLED fabricated by the Ce:YAG single crystal prepared in present work meets all requirements in related GB codes, and its performance is better in comparison with that of the commercially available one, the Ce:YAG single crystal will possibly be used to fabricate new-type WLED devices.

Keyword: WLED; yttrium aluminum garnet doped with Ce; luminescence property; packaging technology; photoelectric property

Show Figures

0 引言

掺杂Ln系离子的钇铝石榴石(Y₃Al₅O₁₂, 简称YAG)在长余辉材料^{[ 1]}、探测高能辐射的闪烁器^{[ 2, 3]}、量子信息存储及计算协议(quantum computation protocols)^{[ 4]}、荧光温度传感器^{[ 5]}、近场显微学^{[ 6]}、生物标记^{[ 7]}以及白光LED^{[ 8, 9]}等领域广泛应用, 特别是白光LED被誉为新一代固态光源而受到广泛关注, 而掺杂Ce的YAG涉足相关领域不到20年。自1996年日本日亚化学公司(Nichia Corporation)商业化GaN蓝光芯片和Ce:YAG荧光粉组合的白光LED后^{[ 10]}, Ce:YAG才作为一种新型光转换荧光材料受到广泛关注和研究, Ce:YAG荧光粉也是目前荧光粉封装白光LED(Phosphor-converted White Light-emitting Diode, pcWLED)中使用最多的黄光转换材料^{[ 11]}。然而, 此荧光粉并不适应未来大功率白光LED的需求^{[ 12]}。这是由于芯片在电-光转换过程中大部分电能损失会转化成热能, 导致分散Ce:YAG荧光粉的树脂在长时间高强度辐照下加速老化, 透过率下降, 光衰增大, 器件使用寿命缩短, 对白光LED的稳定性产生重大影响^{[ 13, 14]}; 荧光粉和树脂折射率不同, 并且荧光粉还存在光散射和自吸收, 降低了出光效率。现今, 高光效、优显色指数和强热稳定性的白光LED成为各国科学工作者努力追求的目标^{[ 15]}, 因此, 人们迫切需要一种新型高性能荧光体来代替荧光粉。

相比之下, YAG单晶透过率高、热导率高、晶体场以及物化性能稳定、生长工艺成熟, 是一种理想的光转换荧光材料。但是, YAG单晶应用于白光LED器件还未有系统报导。2012年陆神洲课题组从Ce:YAG单晶厚度角度研究了其取代Ce:YAG荧光粉制备白光LED的光电性能^{[ 16]}; 2013年日本学者Latynina等^{[ 13]}用Gd掺杂的Ce:YAG单晶封装得到的白光LED在工作电流为40 mA时光效达到 136 lm/W, 却没有改善其显色指数。本工作采用提拉法制备Ce:YAG单晶, 对其光谱特性进行了分析, 探讨了Ce³⁺在YAG晶体中的发光机理以及量化了Ce³⁺在YAG晶体场中的能级, 并用变温光谱揭示了Ce:YAG单晶的热稳定性能; 同时针对芯片、驱动电流、晶片厚度以及红色荧光粉添加物四类因素对封装工艺的影响展开了系统研究。

1 实验方法

1.1 Ce:YAG单晶的制备

将高纯原料Y₂O₃(99.999%)、Al₂O₃(99.999%)、CeO₂(99.999%)按化学式Ce _zY_3- _zAl₅O₁₂(其中 z=0.04)准确称量, 混合均匀后压成素坯, 在1200℃预烧 12 h后装入铱坩埚, 在晶体炉内用提拉法生长得到铈掺杂钇铝石榴石单晶。本实验采用<100>方向的籽晶提拉晶体, 具体参数为: 晶体转速12~20 r/min, 提拉速度1.0~2.0 mm/h, 生长结束后以不大于50℃/h的冷却速率降至室温, 取出 φ28 mm×106 mm, 质量约为230 g的亮黄色Ce:YAG晶体。

1.2 Ce:YAG单晶的封装

实验过程中采用主发光波长为455 nm的GaN芯片作为蓝光光源, 经固晶、焊线制得支架后以镶嵌方式安置Ce:YAG晶片, 封装成白光LED器件, 白光LED实物图见图1(A),封装结构见图1(B)。

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	图1 Ce:YAG单晶制成的白光LED光源(A)和Ce:YAG单晶制得白光LED的封装结构(B)Fig. 1 A sample of WLED fabricated by Ce:YAG single crystal (A) and Package structure of Ce:YAG single crystal for WLED (B)

1.3 表征及性能测试

采用SHIMADZU制UV-2450型紫外-可见分光光谱仪测试吸收光谱, 波长范围200~800 nm, BaSO₄粉末做为标样。采用FluoroMax-4荧光光度计测量激发和发射光谱, 狭缝宽度为1 nm。采用Horiba Jobin Yvon Fluromax-4P光谱仪测量变温发光光谱, 变温设备采用Janis公司的VPF-800液氮型低温恒温器, 变温范围为65～800 K。采用杭州远方ZWL-600光色电综合测试系统测试电光源, 扫描范围380~800 nm, 扫描间隔5 nm, 积分时间80~100 ms, 从晶体同一部位切割不同厚度的晶片作为样品, 厚度为 h₁( h₁= 0.5 mm), 用于封装在M₁型蓝光芯片上; h₂( h₂= 0.4、0.5、1和1.5 mm), 用于封装在M₂型蓝光芯片上(M₁和M₂型蓝光芯片均为目前商用白光LED最常用蓝光芯片之一, 两者的区别主要是出射面积和额定蓝光光通量); 商用白光LED荧光粉型号为XLY555-M(上海祥羚光电科技发展有限公司)。

2 结果和讨论

2.1 吸收光谱分析

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	图2 Ce:YAG单晶的吸收光谱(A)和插图为MN段谱线用Lorentzian和Gaussian函数分峰拟合的结果(B)Fig. 2 The absorption spectrum of Ce:YAG single crystal (A) and The inset shows the typical emission of spectrum in MN band separated into Lorentzian and Gaussian distributions (B)

Ce:YAG单晶在200~800 nm之间的吸收光谱如图2(A)所示, 可以明显看到, 图中存在以202和455.5 nm为中心的强吸收带, 以219 nm为中心的弱吸收带以及230~400 nm之间多中心的混合吸收带。230~400 nm之间的吸收峰用Lorentzian和Gaussian分峰拟合得到247.3、284.7和347.4 nm三处吸收峰。其中, 202、219、247.3、347.4和455.5 nm五处吸收峰, 对应于Ce³⁺离子4f基态²F_5/2到5d激发态子能级之间的跃迁吸收^{[ 17]}; 284.7 nm处的吸收峰对应于Ce³⁺离子最低5d激发态到导带能级的跃迁吸收^{[ 18]}。覆盖在400~500 nm的宽吸收带表明, Ce:YAG单晶可以有效吸收GaN芯片发出的蓝光用于制备白光LED。

2.2 激发发射光谱分析

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	图3 Ce:YAG单晶的激发光谱(A)和发射光谱(B)Fig. 3 Excitation (A) and emission (B) spectra of Ce:YAG single crystal

在YAG晶体中, 具有[Xe]4f¹电子结构的Ce³⁺的基态由于自旋偶合而劈裂为²F_5/2和²F_7/2双重态, 在室温下, 电子占据²F_5/2, 4f能级被屏蔽在内层, 受晶体场作用小, 而5d电子的径向波函数位于5s²5p⁶壳层之外, 因此, 5d能级会受到晶体场的强烈影响; 同时, Ce³⁺离子的4f和5d电子的能量本身很近^{[ 19]}, 导致5d能级发生能级分裂。Ce³⁺(11.43 nm)在YAG晶体中取代的是Y³⁺(10.19 nm)格位, 由于中心离子与配位离子的距离越小会导致越大的晶体场分裂^{[ 20]}, 所以Ce³⁺离子在YAG晶体场下会获得更大的5d能级差。图3(A)为Ce:YAG单晶的激发光谱, 可以看出2个最低的5d能级为491 nm(20366 cm^-1)和343 nm (29154 cm^-1), 491 nm处的激发峰对应4f^{1 2}F_5/2Г_8u→ 5d^{1 2}E_gГ_8g的能级跃迁; 343 nm和466 nm两处出现较强的宽带激发峰, 分别对应于Ce³⁺离子的4f^{1 2}F_5/2Г_7u→5d^{1 2}E_gГ_7g和4f^{1 2}F_5/2Г_7u→5d^{1 2}E_gГ_8g的能级跃迁, 343 nm处激发峰相对较弱。值得注意的是, 在440~480 nm之间激发谱呈现多个尖峰的结构, 除了466 nm处激发峰之外, 还包括449、451、457、461、472和480 nm六处激发峰, 这些激发峰不是由于能级跃迁造成的, 而是因为测试仪器中Xe灯强度的变化导致的, 原则上应该消除, 但是激发谱就是为了修正此强度的变化, 故而对分析不产生影响^{[ 21]}。图3(B)为在波长466 nm蓝光激发下的Ce:YAG单晶发射光谱。当用466 nm蓝光激发Ce³⁺时, 电子从4f基态跃迁到5d激发态后, 大部分电子随即从5d激发态宽能带跃迁回4f基态的²F_7/2和²F_5/2能级, 发射出宽谱带500~700 nm的黄光, 其中发生概率最高的能级跃迁过程是5d^{1 2}E_gГ_8g→4f^{1 2}F_7/2Г_8u, 也就是图中对应的526 nm发射峰, 这与Setlur等^{[ 22]}观测的现象一致, 这种宽谱带的黄光为Ce:YAG单晶进入白光LED领域提供了有力保障。综上, 可得出Ce³⁺在YAG晶体中的Schematic能级图, 如图4(A)所示。依据图2中的各个吸收峰和图3中的各个激发峰, 通过计算可以确定Ce³⁺离子在YAG晶体中4f和5d各个能级能量, 和文献值[23-24]比较吻合, 如图4(B)所示。

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	图4 Ce:YAG单晶中Ce³⁺4f和5d的Schematic能级图(A)和Ce³⁺4f和5d能级的文献值和实验计算值的比较(B)Fig. 4 Schematic diagram of the energy level and band structure of the 4f and 5d configurations of the Ce³⁺ ion in a Ce:YAG single crystal field (A) and comparation between the literature values and experimental values of cerium 4f and 5d energy levels (B)

2.3 变温发光光谱分析

由激发光谱可知Ce:YAG单晶可以被460 nm的蓝光激发出526 nm的黄绿光, 白光LED中蓝光由电致发光原理产生, 即p-GaN中的“空穴”和n-GaN中的“电子”在电场作用下复合, 释放能量以光和热的形式表现出来, 所以白光LED的工作温度要高于常温, 通常在320~370 K之间, 甚至更高^{[ 25]}。为了反映Ce:YAG单晶在工作时的发光性能, 本实验采用变温发光光谱^{[ 14, 26, 27]}, 其被广泛应用于辐射和无辐射弛豫过程以及发光稳定性方面的研究^{[ 28, 29, 30]}。

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	图5 Ce:YAG单晶的变温发光光谱(A)和Ce³⁺的无辐射跃迁过程(B)Fig. 5 Temperature-dependent PL spectra of Ce:YAG single crystal (A) and A schematic illustration of nonradiative transition (B)

Ce离子发光的固有猝灭温度远高于600 K^{[ 21]}, 达到700 K之上^{[ 31]}。从图5(A)中可以看出, 温度范围在320~500 K之间时, 随着温度的升高, 发光强度降低, 但是变化幅度不大, 500 K发光强度比320 K的下降13.28%, 相对于Ce:YAG荧光粉发光强度下降30%^{[ 21]}而言要小得多。在低浓度掺杂的情况下对发射光谱强度起主要作用的是振子强度, 发光强度的下降是由于Ce离子的²F_7/2能级能量在一定热量的晶体场下会变强, 一部分热激发中心发生了无辐射跃迁, 能量变化过程是M→N→S→K, 见图5(B), 导致了发光强度随温度升高而降低; 同时²F_7/2能级能量的升高导致最易跃迁的能量降低, 使得发光峰位置发生红移, 一定程度上弥补了Ce:YAG单晶红光部分的缺失, 正如图5(A)所示, 发光峰从537 nm处红移至550 nm处。X射线激发Ce:YAG变温光谱存在类似现象^{[ 32]}。综上, 以Ce:YAG单晶作为荧光材料的白光LED在工作环境中更具优势。

2.4 Ce:YAG单晶封装工艺研究

综合上述分析可知, Ce:YAG单晶应用于白光LED领域比荧光粉更具优势。在利用Ce:YAG单晶封装白光LED时, 必须考虑所用蓝光芯片、驱动电路所用工作电流、Ce:YAG单晶片的厚度和有无红色荧光粉等四种因素对封装工艺的影响。

2.4.1 蓝光芯片

选用目前占有商用白光LED市场份额较大的两种芯片—M₁型和M₂型芯片, 分别测试它们以及涂覆硅氧烷类树脂胶(以下统称AB胶^{[ 33]})的光电参数如表1所示。从表1中可以看出, 在额定功率下, 色温、显色指数以及色坐标相对稳定, 说明不同型号的芯片出射的蓝光波长范围保持一致; 在涂覆了AB胶之后, 尽管M₁和M₂芯片内部结构不一样, 但是蓝光的光通量和光效相差不大。由此可以根据实际需求来选用不同的芯片类型。

表1 不同芯片的光电参数 Table 1 Photoelectric parameters of different chips

2.4.2 驱动电流

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	图6 Ce:YAG单晶制白光LED用不同芯片在变化的驱动电流下的色坐标Fig. 6 Colour coordinates of WLEDs fabricated by the Ce: YAG single crystal ( z=0.04) and different chips under changeable currentsThe inset obviously shows the changeable tendency of colour coordinates of WLEDs fabricated by the Ce:YAG single crystal ( z=0.04) and different chips under different currents

表2 Ce:YAG单晶制白光LED在不同的驱动电流下的光电参数 Table 2 Photoelectric parameters of WLEDs fabricated by the Ce:YAG single crystal ( z=0.04) under changeable currents

将施加在驱动电路两端的工作电流从350 mA降至20 mA测得的Ce:YAG单晶封装白光LED的光电参数如表2所示, 从表中可以明显看出随着驱动电流的升高, (i)光效急剧下降, 这是由于 I_F× V_F变化的幅度要远远大于光通量的变化幅度, 此与文献[13]报导结果一致; (ii)色坐标沿着黑体辐射曲线方向向冷白光处移动(见图6), 这是由于驱动电流的升高导致了蓝光光通量的增加, 变相减小了最终白光中红颜色和绿颜色的比例, 直观的来看就是色坐标的 x和 y值减小; (iii)色温不断增大, 也会表现出白光越来越冷, 这是由于色温 T与色坐标( x, y)之间存在函数关系^{[ 16]}, 如式(1)所示, n为( x, y)与(0.3320, 0.1858)之间的偏差值, n值不断减小, T值反向逐渐增大; (iv)显色指数不断增大, 这是由于显色指数反映的是测试光源在同色温的基准下与8种色彩的偏移, 色温不断增大的趋势反映了Ce:YAG单晶被蓝光激发所发光中缺乏红光成分的特性, 从而使显色指数不断增大。总的来看, 要想获得越低色温和越高光效的Ce:YAG单晶制白光LED需要采用尽量低的驱动电流。

(1)

2.4.3 晶片厚度

在芯片额定电流工作下, 将Ce_0.04:YAG单晶切成0.4、0.5、1和1.5 mm四种厚度的晶片, 其光电参数测试结果如表3所示。晶片厚度不断增加, 色坐标的 x和 y值不断增大, 所出射的光逐渐从白光区过渡到黄光区。比较发现, 当晶片厚度为0.5 mm时, Ce:YAG单晶封装白光LED的各项参数均处于理想位置, 所以芯片在额定电流下发出的蓝光光通量在3.7 lm左右时, 运用Ce_0.04:YAG单晶封装白光LED最佳晶片厚度为0.5 mm, 此结果可以指导Ce:YAG单晶应用于白光LED领域。

表3 Ce:YAG单晶制白光LED在不同晶片厚度下的光电参数 Table 3 Photoelectric parameters of WLEDs fabricated by the Ce:YAG single crystal ( z=0.04) with different thicknesses

2.4.4 红色荧光粉

由图3(B)可知Ce:YAG单晶的发射峰在526 nm处, 虽然其有500~700 nm的宽发射带, 但是谱线大多落在黄绿光区, 可见Ce:YAG单晶缺乏红光区的发射光, 这正是其显色指数始终在70以下的原因。为了改善这种状况, 在AB胶中适当添加蓝光激发红色荧光粉是一种有效途径。表4给出了添加不同质量百分比的红粉(SrS:Eu²⁺荧光粉, 发射峰在600~ 660 nm之间)光源的光电参数, 可以看出除了光效小幅下降之外, 色坐标和色温相对稳定, 显色指数得到大幅度提升, 一般在10以上。所以适当运用红粉扩展了Ce:YAG单晶制白光LED的使用范围。

表4 Ce:YAG单晶制白光LED中添加红粉的光电参数 Table 4 Photoelectric parameters of WLEDs fabricated by the Ce:YAG single crystal ( z=0.04) and red phosphors

2.4.5 初步结果

选用M₂型蓝光芯片, Ce:YAG晶片厚度为0.5mm, 涂覆AB胶和红粉混胶, 经过固化后得到白光LED光源成品的光电参数如表5所示。和商业荧光粉制得的暖白LED数据比较可知, 除了色温略高之外, 光效和显色指数都明显优于商业暖白LED, 尤其是显色指数达到了81.9, 已符合国家室内照明标准I级标准^{[ 34]}。可见, 此法封装的白光LED具有优良性能, Ce:YAG单晶有望应用于白光LED领域。

表5 Ce:YAG单晶制白光LED光源和商业白光LED的光电参数 Table 5 Photoelectric parameters of WLEDs fabricated by eithor Ce:YAG single crystal ( z=0.04) or commercial phosphors

3 结论和展望

采用提拉法生长的铈掺杂钇铝石榴石单晶的光学性能已经被表征, 能被466 nm波长的蓝光有效激发, 产生500~700 nm范围内的宽化发射峰。Ce³⁺的4f→5d轨道的跃迁吸收对应于202、219、247.3、347.4和455.5 nm五个吸收峰, 由此可量化分裂的5d能级能量, 从低到高依次为21954、29154、40437、45662和49505 cm^-1。由变温光谱结果可以看出Ce:YAG晶体中Ce³⁺的²F_7/2能级能量的升高导致了发光强度的降低, 但是降低幅度(13.28%)远远小于Ce:YAG荧光粉在同等条件下的降低幅度(30%)。由此, Ce:YAG单晶在白光LED工作环境中更具优势。针对Ce:YAG单晶封装白光LED的工艺研究表明当驱动电流在额定状态且蓝光光通量在3.7 lm左右时, Ce:YAG晶片的适宜厚度为0.5 mm, 适当添加红粉再经固化处理后制得的白光LED光源达到国家照明标准I级分类标准, 且要优于目前商用荧光粉制白光LED光源。因此, Ce:YAG单晶是一种重要的Ce:YAG荧光粉替代物应用于白光LED产业, 乃至新提出的无树脂封装大功率白光LED领域。

参考文献

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2011

1.363

0.7325

J. Rare Earths. 2011, 29(5):426-430 DOI:10.1016/S1002-0721(10)60473-5

Long-lasting phosphorescence study on Y₃Al₅O₁₂ doped with different concentrations of Ce³+

Abstract

Long-lasting phosphorescence (LLP) was observed in Ce-doped Y₃Al₅O₁₂ phosphors synthesized in reducing atmosphere. The characteristic emission of the ²D-²F_5/2 and ²D-²F_7/2 transition of Ce³⁺ in photoluminescence (PL) and LLP spectra was studied. It was interesting that the ratio between the peak areas of ²D-²F_5/2 and ²D-²F_7/2 transitions in the PL spectrum was different from the ratio of that in LLP emission spectrum. And the ratios had different change regularities with increased Ce³⁺ concentration. The possible reason was attributed to the defect in the YAG host, which was affected by increasing the Ce³⁺ concentration. There were indications that the defect in the Ce³⁺-doped YAG samples was strongly associated with oxygen vacancy. And the defect levels were studied through thermoluminescence (TL) experiment. The results showed that the trap depth was between 0.6 and 0.65 eV, and the kinetic order of the LLP was 2.

... 0 引言掺杂Ln系离子的钇铝石榴石(Y₃Al₅O₁₂, 简称YAG)在长余辉材料^[1]、探测高能辐射的闪烁器^[2,3]、量子信息存储及计算协议(quantum computation protocols)^[4]、荧光温度传感器^[5]、近场显微学^[6]、生物标记^[7]以及白光LED^[8,9]等领域广泛应用, 特别是白光LED被誉为新一代固态光源而受到广泛关注, 而掺杂Ce的YAG涉足相关领域不到20年 ...

2007

2.144

0.0

J. Lumin.. 2007, 126(1):null-null

Luminescence and scintillation properties of YAG:Ce single crystal and optical ceramics

2009

0.0

2011

38.597

0.0

Nature. 2011, 469(7331):508-511

Quantum storage of photonic entanglement in a crystal

Entanglement is the fundamental characteristic of quantum physics—much experimental effort is devoted to harnessing it between various physical systems. In particular, entanglement between light and material systems is interesting owing to their anticipated respective roles as ‘flying’ and stationary qubits in quantum information technologies (such as quantum repeaters^{1, 2, 3} and quantum networks⁴). Here we report the demonstration of entanglement between a photon at a telecommunication wavelength (1,338 nm) and a single collective atomic excitation stored in a crystal. One photon from an energy–time entangled pair⁵ is mapped onto the crystal and then released into a well-defined spatial mode after a predetermined storage time. The other (telecommunication wavelength) photon is sent directly through a 50-metre fibre link to an analyser. Successful storage of entanglement in the crystal is proved by a violation of the Clauser–Horne–Shimony–Holt inequality⁶ by almost three standard deviations (S = 2.64 ± 0.23). These results represent an important step towards quantum communication technologies based on solid-state devices. In particular, our resources pave the way for building multiplexed quantum repeaters⁷ for long-distance quantum networks.

2008

0.0

2012

10.015

0.0

2004

3.829

0.0

2009

27.254

0.0

Nature Photonics. 2009, 3(4):180-182

Prospects for LED lighting

More than one-fifth of US electricity is used to power artificial lighting. Light-emitting diodes based on group III/nitride semiconductors are bringing about a revolution in energy-efficient lighting.

2008

3.794

0.0

1997

0.0

... 自1996年日本日亚化学公司(Nichia Corporation)商业化GaN蓝光芯片和Ce:YAG荧光粉组合的白光LED后^[10], Ce:YAG才作为一种新型光转换荧光材料受到广泛关注和研究, Ce:YAG荧光粉也是目前荧光粉封装白光LED(Phosphor-converted White Light-emitting Diode, pcWLED)中使用最多的黄光转换材料^[11] ...

2012

1.913

0.0

Mater. Res. Bull.. 2012, 47(5):null-null

Yellow-emitting (Ca₂Lu₁-_xCe_x) (ScMg)Si₃O₁₂ phosphor and its application for white LEDs

2007

0.0

... 然而, 此荧光粉并不适应未来大功率白光LED的需求^[12] ...

2013

2.39

0.0

J. Alloys Compd.. 2013, 553:null-null

Properties of Czochralski grown Ce,Gd:Y₃Al₅O₁₂ single crystal for white light-emitting diode

... 这是由于芯片在电-光转换过程中大部分电能损失会转化成热能, 导致分散Ce:YAG荧光粉的树脂在长时间高强度辐照下加速老化, 透过率下降, 光衰增大, 器件使用寿命缩短, 对白光LED的稳定性产生重大影响^[13,14] ...

... 2013年日本学者Latynina等^[13]用Gd掺杂的Ce:YAG单晶封装得到的白光LED在工作电流为40 mA时光效达到 136 lm/W, 却没有改善其显色指数 ...

2004

1.552

0.0

J. Cryst. Growth. 2004, 268(3/4):null-null

Solid-state lighting: failure analysis of white LEDs

... 为了反映Ce:YAG单晶在工作时的发光性能, 本实验采用变温发光光谱^[14,26,27], 其被广泛应用于辐射和无辐射弛豫过程以及发光稳定性方面的研究^[28,29,30] ...

2011

2.771

0.0

... 现今, 高光效、优显色指数和强热稳定性的白光LED成为各国科学工作者努力追求的目标^[15], 因此, 人们迫切需要一种新型高性能荧光体来代替荧光粉 ...

2012

0.0

... 2012年陆神洲课题组从Ce:YAG单晶厚度角度研究了其取代Ce:YAG荧光粉制备白光LED的光电性能^[16] ...

... (iii)色温不断增大, 也会表现出白光越来越冷, 这是由于色温T与色坐标(x,y)之间存在函数关系^[16], 如式(1)所示, n为(x,y)与(0 ...

2007

2.355

0.0

... 5 nm五处吸收峰, 对应于Ce³⁺离子4f基态²F_5/2到5d激发态子能级之间的跃迁吸收^[17] ...

1981

0.71

0.0

... 7 nm处的吸收峰对应于Ce³⁺离子最低5d激发态到导带能级的跃迁吸收^[18] ...

2003

10.677

0.0

J. Am. Chem. Soc.. 2003, 125(43):13225–13233-null

Absorption and Emission Spectra of Ce³⁺ in Elpasolite Lattices

Peter A. Tanner ,* † Chris S. K. Mak , † Norman M. Edelstein ,* ‡ Keith M. Murdoch , ‡ Guokiu Liu , § Jin Huang , ‖ Luis Seijo , and Zoila Barandiarán ;

<div>Contribution from the Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR. Peoples' Republic of China; Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8175; Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439; Department of Physics and Astronomy, University of Wisconsin, Eau Claire, Wisconsin 54702; and Departamento de Quíimica, C-XIV and Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid, Spain</div><div></div>

The experimental determination of the electronic energy levels for Ce³⁺ in some chloroelpasolite hosts for both the ground 4f¹ and the excited 5d¹ configurations is described. High-resolution f−f absorption and f−²T_2g d absorption and emission spectra have been recorded at low temperatures for Ce³⁺ diluted into various hexachloroelpasolite lattices. A fluorescence spectrum at

50 000 cm^-¹ is tentatively assigned to the emission from the highest 5d crystal field level, ²E_g, of a Ce³⁺ impurity in Cs₂NaErCl₆, enabling the values of all the energy levels of both the 4f¹ and 5d¹ configurations to be given for Ce³⁺ in elpasolite hosts. Vibronic structure superimposed on the electronic transitions is analyzed in terms of a simple configurational coordinate model involving the ground and excited configurations. It is found that the difference in the Ce−Cl bond length between the 4f¹ and 5d¹ configurations is

0.04 Å. Ab initio model potential calculations on the (CeCl₆)³^- cluster embedded in a reliable representation of the Cs₂NaYCl₆ host support these conclusions.

... 同时, Ce³⁺离子的4f和5d电子的能量本身很近^[19], 导致5d能级发生能级分裂 ...

2012

2.771

0.0

J. Phys. Chem. A. 2012, 116(33):8464–8474-null

Luminescence and Energy Transfer in Lu₃Al₅O₁₂ Scintillators Co-Doped with Ce³⁺ and Tb³⁺

Joanna M. Ogiegło † , Aleksander Zych † , Konstantin V. Ivanovskikh † ‡ , Thomas Jüstel § , Cees R. Ronda * † , and Andries Meijerink †

<div id="aff1"><sup>†</sup> CMI, Debye Institute for Nanomaterials Science, <span class="institution">Utrecht University</span>, P O. Box 80 000, 3508 TA Utrecht, The Netherlands</div><div id="aff2"><sup>‡</sup> Department of Physics and Astronomy, <span class="institution">University of Canterbury</span>, Private Bag 4800, Christchurch 8020, New Zealand</div><div id="aff3"><sup>§</sup> <span class="institution">University of Applied Sciences Münster</span>, 48565 Steinfurt, Germany</div><div id="aff4"><sup><img src="/appl/literatum/publisher/achs/journals/entities/2225.gif" alt="" class="entityA" align="absbottom" /></sup> <span class="institution">Philips Research Europe-Eindhoven</span>, High Tech Campus 4, 5656 AE Eindhoven, The Netherlands</div><div id="aff5"><sup><img src="/appl/literatum/publisher/achs/journals/entities/22A5.gif" alt="" class="entityA" align="bottom" /></sup> Centre for Optical and Electromagnetic Research, <span class="institution">Zhejiang University</span>, Hangzhou 310058, China</div><div>*E-mail: <a href="mailto:cees.ronda@philips.com">cees.ronda@philips.com</a>.</div>

Lu₃Al₅O₁₂ (LuAG) doped with Ce³⁺ is a promising scintillator material with a high density and a fast response time. The light output under X-ray or γ-ray excitation is, however, well below the theoretical limit. In this paper the influence of codoping with Tb³⁺ is investigated with the aim to increase the light output. High resolution spectra of singly doped LuAG (with Ce³⁺ or Tb³⁺) are reported and provide insight into the energy level structure of the two ions in LuAG. For Ce³⁺ zero-phonon lines and vibronic structure are observed for the two lowest energy 5d bands and the Stokes’ shift (2 350 cm^–1) and Huang–Rhys coupling parameter (S = 9) have been determined. Tb³⁺ 4f–5d transitions to the high spin (HS) and low spin (LS) states are observed (including a zero-phonon line and vibrational structure for the high spin state). The HS–LS splitting of 5400 cm^–1 is smaller than usually observed and is explained by a reduction of the 5d–4f exchange coupling parameter J by covalency. Upon replacing the smaller Lu³⁺ ion with the larger Tb³⁺ ion, the crystal field splitting for the lowest 5d states increases, causing the lowest 5d state to shift below the ⁵D₄ state of Tb³⁺ and allowing for efficient energy transfer from Tb³⁺ to Ce³⁺ down to the lowest temperatures. Luminescence decay measurements confirm efficient energy transfer from Tb³⁺ to Ce³⁺ and provide a qualitative understanding of the energy transfer process. Co-doping with Tb³⁺ does not result in the desired increase in light output, and an explanation based on electron trapping in defects is discussed.

... 19 nm)格位, 由于中心离子与配位离子的距离越小会导致越大的晶体场分裂^[20], 所以Ce³⁺离子在YAG晶体场下会获得更大的5d能级差 ...

2009

8.238

0.0

Chem. Mater.. 2009, 21(10):2077–2084-null

Temperature Quenching of Yellow Ce³⁺ Luminescence in YAG:Ce

Volker Bachmann † ‡ , Cees Ronda † ‡ and Andries Meijerink * †

<div id="aff1">Chemistry and Physics of Condensed Matter, Debye Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands, and Philips Technology GmbH Research Laboratories, Weisshausstr. 2, D-52066 Aachen, Germany</div><div>* To whom correspondence should be addressed. E-mail: <a href="mailto:a.meijerink@uu.nl">a.meijerink@uu.nl</a>. Fax: <span class="fax">+31-30-2532204</span>.,† <p class="last">Utrecht University.</p>,‡ <p class="last">Philips Technology GmbH Research Laboratories.</p></div>

Yttrium aluminum garnet (YAG) doped with Ce³⁺ is the phosphor of choice for the conversion of blue to yellow light in the rapidly expanding market of white light LEDs, but it is generally thought to suffer from a low luminescence quenching temperature. The luminescence quenching temperature is an important parameter, especially in high-power LEDs, but surprisingly no systematic research has been done to measure and understand the temperature quenching of the yellow Ce luminescence in YAG:Ce. Here we report on the luminescence temperature quenching in YAG:Ce. For a wide range of Ce concentrations (between 0.033% and 3.3%) the temperature dependence of the emission intensity and the luminescence lifetimes are reported. The intrinsic quenching temperature of the Ce luminescence is shown to be very high (>700 K). The lower quenching temperatures reported in the literature are explained by thermally activated concentration quenching (for highly doped systems) and the temperature dependence of the oscillator strength (for low doping concentrations). In addition, high-resolution spectra are reported, which provide insight into the position of the zero-phonon transition (20450 cm⁻¹), the Stokes shift (2400 cm⁻¹), the energy of the dominant phonon mode (200 cm⁻¹), and the Huang−Rhys parameter (S = 6). These parameters are compared with ab initio calculations on the position of and relaxation in the excited 5d state of Ce³⁺ in YAG, which can aid in providing a better theoretical understanding of the temperature quenching.

... 值得注意的是, 在440~480 nm之间激发谱呈现多个尖峰的结构, 除了466 nm处激发峰之外, 还包括449、451、457、461、472和480 nm六处激发峰, 这些激发峰不是由于能级跃迁造成的, 而是因为测试仪器中Xe灯强度的变化导致的, 原则上应该消除, 但是激发谱就是为了修正此强度的变化, 故而对分析不产生影响^[21] ...

... Ce离子发光的固有猝灭温度远高于600 K^[21], 达到700 K之上^[31] ...

... 28%, 相对于Ce:YAG荧光粉发光强度下降30%^[21]而言要小得多 ...

2006

1.918

0.0

... _8u, 也就是图中对应的526 nm发射峰, 这与Setlur等^[22]观测的现象一致, 这种宽谱带的黄光为Ce:YAG单晶进入白光LED领域提供了有力保障 ...

1992

2.087

0.0

1999

1.534

0.0

Solid State Commun.. 1999, 110(6):null-null

Attribution of the near-UV absorption bands of YAG:Ce to Ce³+-ions by MCD and ODMR

2013

1.482

0.0

Solid-State Electron. 2013, 86:null-null

Analysis of three different junction temperature estimation methods for AC LEDs

... 3 变温发光光谱分析由激发光谱可知Ce:YAG单晶可以被460 nm的蓝光激发出526 nm的黄绿光, 白光LED中蓝光由电致发光原理产生, 即p-GaN中的“空穴”和n-GaN中的“电子”在电场作用下复合, 释放能量以光和热的形式表现出来, 所以白光LED的工作温度要高于常温, 通常在320~370 K之间, 甚至更高^[25] ...

2007

0.0

Science and Technology of Advanced Materials. 2007, 8(7-8):588-null

Silicon-based oxynitride and nitride phosphors for white LEDs—A review

Rong-Jun Xie 1 and Naoto Hirosaki

<p><a href="mailto:Xie.Rong-Jun@nims.go.jp" class="link" title="send mail to Xie.Rong-Jun@nims.go.jp">Xie.Rong-Jun@nims.go.jp</a></p><p><sup></sup>Nitride Particle Group, Nano Ceramics Center, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan<br/><sup>1</sup>Corresponding author.<br/></p>

As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN₄ tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties.

2008

8.238

0.0

Chem. Mater.. 2008, 20(19):6277–6283-null

Incorporation of Si⁴⁺–N³⁻ into Ce³⁺ -Doped Garnets for Warm White LED Phosphors

Anant A. Setlur * † , William J. Heward † , Mark E. Hannah ‡ and Uwe Happek ‡

<div id="aff1">GE Global Research, 1 Research Circle, Niskayuna, New York 12309, and Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602</div><div>* Corresponding author. E-mail: <a href="mailto:setlur@research.ge.com">setlur@research.ge.com</a>.,† <p class="last">GE Global Research.</p>,‡ <p class="last">University of Georgia.</p></div>

The effect of Si⁴⁺−N³⁻ incorporation on Ce³⁺ doped RE₃Al₅O₁₂:Ce³⁺ (RE = Lu³⁺, Y³⁺, or Tb³⁺) garnet phosphors is described in this report. The addition of Si⁴⁺−N³⁻ leads to distinct low-energy Ce³⁺ absorption and emission bands that are assigned to Ce³⁺ ions that have N³⁻ in their local coordination. The combination of the typical Ce³⁺ emission in garnets with the low energy Ce³⁺ emission band results in a broad emission spectrum suited for white LED lamps with low color temperatures and good color rendering using only a single phosphor. The low-energy Ce³⁺ emission band has stronger quenching at high temperatures, a potential limitation. The mechanism for this quenching is discussed.

2007

4.814

0.0

J. Phys. Chem. C. 2007, 111(16):5846–5849-null

Temperature and Size Dependence of Nonradiative Relaxation and Exciton−Phonon Coupling in Colloidal CdTe Quantum Dots

G. Morello ,* † M. De Giorgi , † S. Kudera , † L. Manna , † R. Cingolani , † and M. Anni ‡

<div>Distretto Tecnologico ISUFI and Dipartimento di Ingegneria dell'Innovazione, National Nanotechnology Laboratory (NNL) of CNR-INFM, Università degli Studi di Lecce, Via per Arnesano 73100 Lecce, Italy</div><div></div>

We report on the temperature and size dependence of the photoluminescence of core CdTe colloidal quantum dots (QDs). We show that at temperatures lower than 170 K a thermally activated transition between two different states separated by about 12−20 meV takes place. At temperatures higher than 170 K, the main nonradiative process is thermal escape assisted by multiple longitudinal optical (LO) phonons absorption. Moreover, we show that quantum confinement affects both the exciton−acoustic phonons and the exciton−LO phonons coupling. The coupling constant with acoustic phonons is strongly enhanced in QDs (up to 31μeV/K) with respect bulk CdTe (0.7μeV/K). On the contrary, the exciton-LO phonons coupling constant decreases as the dot size decreases (down to 14 meV with respect 24.5 meV in the bulk).

2009

4.814

0.0

2012

2.144

0.0

J. Lumin.. 2012, 132(7):null-null

Temperature-dependent photoluminescence of CuInS₂ quantum dots

2010

0.0

Mater. Sci. Eng. R. 2010, 71(1):null-null

Phosphors in phosphor-converted white light-emitting diodes: recent advances in materials, techniques and properties

... Ce离子发光的固有猝灭温度远高于600 K^[21], 达到700 K之上^[31] ...

2000

2.355

0.0

Journal of Physics: Condensed Matter. 2000, 12(8):1947-null

Kinetics of cerium emission in a YAG:Ce single crystal: the role of traps

E Zych , , C Brecher and J Glodo ,§

<p><a href="mailto:zych@wchuwr.chem.uni.wroc.pl" class="link" title="send mail to zych@wchuwr.chem.uni.wroc.pl">zych@wchuwr.chem.uni.wroc.pl</a><a href="mailto:cbrecher@chem.bu.edu" class="link" title="send mail to cbrecher@chem.bu.edu">cbrecher@chem.bu.edu</a><a href="mailto:jglodo@phys.uni.torun.pl" class="link" title="send mail to jglodo@phys.uni.torun.pl">jglodo@phys.uni.torun.pl</a></p><p><sup><img alt="-+" src="http://ej.iop.org/icons/daggers/dag.gif"/></sup>Faculty of Chemistry, Wroclaw University, 14 F Joliot-Curie Street, Wroclaw, Poland <br/><sup><img alt="++" src="http://ej.iop.org/icons/daggers/ddag.gif"/></sup>Chemistry Department, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, USA <br/><sup>§</sup>Institute of Physics, N Copernicus University, Grudziadzka 5, 87-100 Torun, Poland <br/></p>

We have measured the emission spectra and decay kinetics of Ce-doped YAG under both optical and gamma excitation, at temperatures ranging from 60 to 600 K. The decay traces under gamma excitation display an unusual pattern of temperature dependence. Beginning with the lowest temperatures, the characteristic time constant of the decay coincides with the intrinsic (radiative) decay time up to about 180 K, at which point it suddenly jumps by more than 30%. The decay time remains longer than radiative until well above room temperature, then gradually reverts to the intrinsic value. This behaviour can be explained in terms of an array of shallow traps, whose existence is confirmed by the presence of thermoluminescent glow peaks. Depending on temperature, one or more of these traps acts as a temporary way-station for the free carriers that carry the excitation to the Ce ion, delaying its emission beyond what would be required by radiative decay alone.

... X射线激发Ce:YAG变温光谱存在类似现象^[32] ...

0.0

... 选用目前占有商用白光LED市场份额较大的两种芯片—M₁型和M₂型芯片, 分别测试它们以及涂覆硅氧烷类树脂胶(以下统称AB胶^[33])的光电参数如表1所示 ...

0.0

... 9, 已符合国家室内照明标准I级标准^[34] ...