【作者】 乔君；

【导师】 张家骅； 蒋大鹏；

【作者基本信息】 中国科学院研究生院(长春光学精密机械与物理研究所) ， 凝聚态物理， 2014， 博士

【摘要】 白光发光二极管（LEDs）具有效率高、寿命长、无污染等优点，有望在将来取代白炽灯和荧光灯成为新一代的照明光源。目前，商业化的白光LED主要是由高性能的InGaN蓝光LED芯片和具有石榴石结构的Y3Al5O12:Ce3+（YAG:Ce3+）黄色荧光粉组成。YAG:Ce3+具有较高的光转换效率，但是其发射光谱中缺少红光成分，导致合成白光LED的显色指数偏低（Ra<80）。为了解决这一问题，获得高显色性的白光LED，人们提出用绿色和红色荧光粉的组合来替代单一的YAG:Ce3+黄色荧光粉。这种方案可以有效提高白光LED的红光发射成分，但是，不同荧光粉之间存在的再吸收问题会造成发光效率的损失。另外，不同荧光粉之间还存在老化特性和温度特性不一致的问题，会导致白光LED的色彩特性随使用时间和温度的变化而变化。因此，单一基质高显色性白光LED荧光粉成为人们研究的热点。Ca3Sc2Si3O12(CSS):Ce3+荧光粉由于具有较高的发光效率和良好的热稳定性引起了人们的重视，其发射光谱是峰值位于505nm的绿光发射带。为了获得单一基质高显色性的白光LED荧光粉，我们通过氮化和共掺杂的方法对CSS:Ce3+荧光粉进行了改造。最终，将此绿色荧光粉改造成了基于蓝光激发的单一基质白光LED用荧光粉，与蓝光LED芯片组合，获得了显色性较高的白光。主要的研究内容及结果如下：（1）对绿色CSS:Ce3+荧光粉进行氮化，可以在保留原有绿光Ce3+发射中心（记为Ce3+(I)）的同时，形成N3-部分配位的红光Ce3+发射中心（记为Ce3+(II)）。Ce3+(I)的发射光谱是峰值位于505nm的绿光发射带，Ce3+(II)的发射光谱是峰值位于610nm的红光发射带。通过改变合成原料中CeO2和Si3N4的含量，我们制备了两个系列的样品（CSS:0.06Ce3+, yN3-和CSS:xCe3+,0.6N3-），并且研究了这些样品的漫反射谱和发射光谱随x、y值变化的规律。在样品CSS:0.06Ce3+, yN3-中，由于电荷补偿作用，N3-含量的增加可以提高CSS中总的Ce3+离子浓度，尤其是Ce3+(II)离子的浓度。在样品CSS:xCe3+,0.6N3-中，当掺杂Ce3+离子的摩尔浓度低于0.008时，Ce3+(I)优先形成，Ce3+(II)几乎不形成。只有当Ce3+离子掺杂浓度大于0.008时，Ce3+(II)才开始形成。通过Ce3+(I)→Ce3+(II)能量传递，我们在样品CSS:Ce3+, N3-中实现了蓝光激发下红绿比可调的系列光谱，使得CSS:Ce3+, N3-荧光粉成为单一基质高显色性的白光LED用荧光粉。将我们制得的单一基质CSS:0.15Ce3+,0.6N3-荧光粉与蓝光LED芯片（λ=450nm）组合，获得显色指数为92、相关色温为6345K、色坐标为（0.31，0.30）的白光。（2）在Ce3+和Pr3+共掺的CSS中，我们研究了Ce3+→Pr3+能量传递对样品发光特性的影响，Ce3+和Pr3+掺入CSS基质时均取代Ca2+的位置。通过Ce3+→Pr3+能量传递，我们在样品的光谱中实现了Pr3+离子位于610nm的红光发射，此发射源于Pr3+离子的1D2-3H4跃迁辐射。随着Pr3+浓度的增加，Ce3+→Pr3+能量传递效率的提高，Pr3+离子位于610nm的红光发射逐渐增强。但是，由于Pr3+与Ca2+之间的电荷失配，导致CSS中Pr3+的实际浓度偏低，为了探索提高CSS中Pr3+浓度的方法，我们引入Mg2+取代基质中的Sc3+来补偿Pr3+与Ca2+之间的电荷失配。结果表明Mg2+的添加不仅能提高CSS中Ce3+的浓度使其发射光谱显著红移，而且能提高CSS中Pr3+的浓度使其发射明显增强。将我们制得的单一基质CSS:0.05Ce3+,0.01Pr3+,0.3Mg2+荧光粉与蓝光LED芯片（λ=450nm）组合，获得显色指数为80、相关色温为8715K、色坐标为（0.28，0.32）的白光。为了获得更高显色性的白光，需要进一步提高此荧光粉的红光发射成分。（3）Mn2+离子掺入CSS晶格时不仅能占据Ca2+离子的位置，产生一个峰值位于574nm的黄光发射带（记为Mn2+(I)）；而且能占据Sc3+离子的位置，产生一个峰值位于680nm的红光发射带（记为Mn2+(II)）。通过Ce3+→Mn2+(Mn2+(I)和Mn2+(II)), Ce3+→Pr3+和Mn2+(I)→Pr3+能量传递，我们在Ce3+、Pr3+和Mn2+共掺的CSS中实现了可调的全光谱发射。随着Mn2+含量的增加，样品光谱中Mn2+(I)和Mn2+(II)发射带逐渐增强的同时，位于610nm的Pr3+离子红光发射也逐渐增强。原因是由于电荷补偿的作用，Mn2+(II)取代Sc3+促进了Pr3+取代Ca2+,提高了CSS中Pr3+离子的实际浓度。另外，我们还研究了Mg2+离子的掺入对样品CSS:Ce3+,Pr3+, Mn2+发光特性的影响。结果表明：随着Mg2+名义含量的增加，样品中Ce3+、Pr3+和Mn2+(I)的浓度逐渐增加，Mn2+(II)的浓度逐渐减少，导致相应光谱中Ce3+发射谱的红移，Mn2+(I)、Pr3+发射的增强和Mn2+(II)发射的减弱。将我们制得的单一基质CSS:0.08Ce3+,0.01Pr3+,0.3Mn2+,0.2Mg2+荧光粉与蓝光LED芯片（λ=450nm）封装，获得了显色指数为90、相关色温为4980K、色坐标为（0.34，0.31）的白光。更多还原

【Abstract】 White light emitting diodes (LEDs) are considered to be a promising candidatefor the future lighting system because of their higher efficiency, longer lifetime, andlack of requirement for pollutants compared with the conventional light sources suchas incandescent lamps or fluorescent lamps. Until now, the most widely usedcommercial white LEDs are fabricated by combining high performance blue-emittingInGaN chip with Y3Al5O12:Ce3+(YAG:Ce3+) yellow emitting aluminate garnetphosphor. YAG:Ce3+has a high converting efficiency, but the deficient red emittingcomponent leads to the color rendering index (CRI) of the white LEDs below80. Toresolve this problem, the method of mixing green and red phosphors instead ofYAG:Ce3+phosphor has been proposed. Unfortunately, the phosphor mixture givesfluorescence reabsorption that result in loss of luminous efficiency. In addition,non-uniformity of luminescent properties for different phosphors will result intime-dependent shift of the color point. Therefore, to achieve single phase phosphorwith full color emission is expected.The green-emitting Ca3Sc2Si3O12(CSS):Ce3+phosphor has attracted muchattention due to its higher luminous efficiency and excellent thermal stability.CSS:Ce3+phosphor exhibits a green-emitting band with a peak at505nm. In order toachieve single phase phosphor with full color emission, we have modified thisphosphor by employing approaches of nitriding and codoping. The main studies andresults are listed as follow:(1) We performed N3-incorporation into CSS:Ce3+and then achievedred-emitting Ce3+centers (peaked at610nm) that have N3-in their local coordination.Diffuse reflectance and photoluminescence spectra for O2-fully coordinated green emitting Ce3+and N3-partially coordinated red Ce3+in CSS:Ce3+, N3-are studied as afunction of CeO2and Si3N4contents in the raw material. Our results indicate that thepresence of N3-can enhance the Ce3+solubility in CSS by Ce3+-N3-substitution forCa2+-O2-. At low Ce3+concentration, the green Ce3+forms preferentially while the redCe3+hardly forms even if N3-content in the raw material is sufficient. There exists athreshold green Ce3+concentration (0.008) for generating red Ce3+. Only beyond thethreshold, the red Ce3+can form. We obtained color tunable luminescence withenhanced red/green intensity ratios through energy transfer from the green Ce3+to redCe3+as only the green Ce3+is excited by blue light. A white LED with CRI of92,CCT of6345K and chromaticity coordinates of (0.31,0.30) is obtained by combiningour single CSS:0.15Ce3+,0.6N3-phosphor with a blue-emitting InGaN LED chip (450nm).(2) In the Ce3+and Pr3+co-activated CSS, Ce3+and Pr3+both occupy the Ca2+sites. We have investigated the effect of Ce3+-Pr3+energy transfer on the luminescenceproperties. The luminescence spectra exhibit a red emission around610nm originatedfrom1D2→3H4transition of Pr3+through the energy transfer from Ce3+to Pr3+. Thered emission of Pr3+gradually enhances with the increase of energy transfer efficiencythat is caused by the increasing concentration of Pr3+in CSS. The amount of Pr3+incorporated into the phosphor is very limited due to the charge mismatch betweenPr3+and Ca2+. In order to explore the approach for enhancing the Pr3+concentration inCSS, we have tentatively added Mg2+in Sc3+site to compensate the residual positivecharge caused by the substitution of Pr3+for Ca2+in CSS. Our results indicate that theaddition of Mg2+can not only increase Ce3+concentration in CSS to make emissionspectra move toward longer wavelength, but also promote Pr3+incorporation into CSSlattices to enhance the Pr3+emission. Finally, A white LED with CRI of80, CCT of8715K and chromaticity coordinates of (0.28,0.32) was fabricated by combining thesingle CSS:0.05Ce3+,0.01Pr3+,0.3Mg2+phosphor with a blue-emitting InGaN LED(450nm) chip. However, this white LED needs more red emission component to beexcellent lighting source. In order to improve the performance of this white LED,further exploration to enhance the red emission of this phosphor is necessary.(3) The introduced Mn2+in CSS lattices can occupy not only Ca2+site to generatea yellow emission band around574nm (named Mn2+(I)) but also Sc3+site to generatea red emission band around680nm (named Mn2+(II)). Through the efficientCe3+→Mn2+(Mn2+(I) and Mn2+(II)), Ce3+→Pr3+and Mn2+(I)→Pr3+energy transfer, we have realized color tunable luminescence in the Ce3+, Pr3+and Mn2+co-activatedCSS. With the enhancement of Mn2+(Mn2+(I) and Mn2+(II)) emissions caused byincreasing Mn2+nominal content, the red emission (around610nm) of Pr3+alsoenhances. The reason may be that the formation of Mn2+(II) that substitutes for Sc3+can enhance the concentration of Pr3+in Ca2+site due to charge compensation effect.In addition, the emission of our present phosphor is also adjusted by addition of Mg2+,due to the Mg2+incorporated into Sc3+site can influence the concentrations of Ce3+,Pr3+and Mn2+(Mn2+(I) and Mn2+(II)) in our phosphor. Finally, A white LED withCRI of90, CCT of4980K and chromaticity coordinates of (0.34,0.31) is obtained bycombining the single CSS:0.08Ce3+,0.01Pr3+,0.3Mn2+,0.2Mg2+phosphor with ablue-emitting InGaN LED chip.更多还原