钪硅酸盐白光LED荧光粉的研究

	钪硅酸盐白光LED荧光粉的研究
	乔君
学位类型	博士
导师	张家骅
	2014-07
学位授予单位	中国科学院大学
学位专业	凝聚态物理
摘要	相比于传统的照明光源（白炽灯和荧光灯），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，广泛应用的商业化白光LED主要是通过结合高性能的InGaN蓝光LED芯片和具有石榴石结构的Y3Al5O12:Ce3+ (YAG:Ce3+)黄色荧光粉来实现。YAG:Ce3+有较高的转化效率，但是其发射光谱中缺少红光成分，导致合成白光LED的显色指数较低(Ra<80)。为了解决这一问题，获得性能优越的白光LED，人们提出用绿色和红色荧光粉的组合来替代YAG:Ce3+黄色荧光粉。但是，这种混粉的方案往往存在着不同荧光粉之间再吸收的问题，会造成发光效率的损失。另外，不同荧光粉还存在发光特性不一致的问题，导致白光LED的色彩特性不稳定。因此，研制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505 nm的绿光发射带。为了获得单一基质高显色性的白光LED用荧光粉，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）我们对绿色CSS:Ce3+荧光粉进行了氮化，在保留原有绿光Ce3+发射中心的同时，形成了N3-部分配位的红光Ce3+发射中心。通过改变合成原料中CeO2和Si3N4的含量，研究了CSS:Ce3+, N3-荧光粉中绿光Ce3+中心和红光Ce3+中心的漫反射谱和发射光谱的变化规律。结果表明：由于电荷补偿的原因，N3-的掺入明显地提高了CSS中Ce3+离子的浓度，并且，我们发现在较低Ce3+掺杂浓度时，绿光Ce3+中心优先形成，红光Ce3+中心几乎没有。只有当Ce3+掺杂浓度达到一定阈值（0.008）时，红光Ce3+中心才明显地形成。通过绿光Ce3+中心向红光Ce3+中心的能量传递，我们实现了蓝光激发下红绿比可调的系列光谱，使得氮化之后的CSS:Ce3+, N3-荧光粉成为一种单一基质的白光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=450 nm）组合，获得显色指数为92、色温为6345 K和色坐标为（0.31，0.30）的白光LED。（2）在Ce3+和Pr3+共掺的CSS中，我们研究了Ce3+-Pr3+能量传递对材料发光性能的影响，其中，Ce3+和Pr3+掺入CSS基质时均取代Ca2+的位置。通过Ce3+-Pr3+能量传递，光谱中出现了位于610 nm的Pr3+红光发射，此发射源于Pr3+的1D2-3H4跃迁。随着Pr3+浓度的增加，Ce3+-Pr3+能量传递效率逐渐提高，Pr3+位于610 nm的红光发射逐渐增强。但是，由于Pr3+与Ca2+之间的电荷失配，导致材料中实际的Pr3+浓度偏低，为了探索提高材料中Pr3+浓度的方法，我们引进Mg2+取代Sc3+的位置来补偿Pr3+和Ca2+之间的电荷失配。结果表明Mg2+的添加不仅能提高材料中Ce3+的浓度使其发射光谱明显红移，而且能提高材料中Pr3+的浓度使其发射明显增强。最终将绿色荧光粉CSS:Ce3+改造成单一基质的白光LED荧光粉，将其用于白光LED，我们获得了显色指数为80，相关色温为8715 K的白光LED。为了进一步改善白光LED的性能，获得更高显色指数和更低色温的白光LED，需要对此荧光粉做进一步的改进，使其发射谱中含有更丰富的红光成分。（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574 nm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680 nm的红光发射带(记为Mn2+(II))。通过Ce3+→Mn2+ (Mn2+(I) and 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610 nm处的Pr3+离子红光发射也逐渐增强。原因可能是由于电荷补偿的作用，Mn2+(II)取代Sc3+促进了Pr3+取代Ca2+, 提高了材料中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=450 nm）封装获得了显色指数为90、色温为4980 K和色坐标为（0.34，0.31）的白光LED。
其他摘要	White light emitting diodes (LEDs) are considered to be a promising candidate for the future lighting system because of their higher efficiency, longer lifetime, and lack of requirement for pollutants compared with the conventional light sources such as incandescent lamps or fluorescent lamps. Until now, the most widely used commercial white LEDs are fabricated by combining high performance blue-emitting InGaN chip with Y3Al5O12: Ce3+ (YAG: Ce3+) yellow emitting aluminate garnet phosphor. YAG: Ce3+ has a high converting efficiency, but the deficient red emitting component leads to the color rendering index (CRI) of the white LEDs below 80. To resolve this problem, the method of mixing green and red phosphors instead of YAG: Ce3+ phosphor has been proposed. Unfortunately, the phosphor mixture gives fluorescence reabsorption that result in loss of luminous efficiency. In addition, non-uniformity of luminescent properties for different phosphors will result in time-dependent shift of the color point. Therefore, to achieve single phase phosphor with full color emission is expected. The green-emitting Ca3Sc2Si3O12 (CSS): Ce3+ phosphor has attracted much attention due to its higher luminous efficiency and excellent thermal stability. CSS: Ce3+ phosphor exhibits a green-emitting band with a peak at 505 nm. In order to achieve single phase phosphor with full color emission, we have modified this phosphor by employing approaches of nitriding and codoping. The main studies and results are listed as follow:(1) We performed N3- incorporation into CSS: Ce3+ and then achieved red-emitting Ce3+ centers (peaked at 610 nm) 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 a function of CeO2 and Si3N4 contents in the raw material. Our results indicate that the presence of N3- can enhance the Ce3+ solubility in CSS by Ce3+-N3- substitution for Ca2+-O2-. At low Ce3+ concentration, the green Ce3+ forms preferentially while the red Ce3+ hardly forms even if N3- content in the raw material is sufficient. There exists a threshold green Ce3+ concentration (0.008) for generating red Ce3+. Only beyond the threshold, the red Ce3+ can form. We obtained color tunable luminescence with enhanced red/green intensity ratios through energy transfer from the green Ce3+ to red Ce3+ as only the green Ce3+ is excited by blue light. A white LED with CRI of 92, CCT of 6345 K and chromaticity coordinates of (0.31, 0.30) is obtained by combining our single CSS: 0.15Ce3+, 0.6N3- phosphor with a blue-emitting InGaN LED chip (450 nm).(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 luminescence properties. The luminescence spectra exhibit a red emission around 610 nm originated from 1D2→3H4 transition of Pr3+ through the energy transfer from Ce3+ to Pr3+. The red emission of Pr3+ gradually enhances with the increase of energy transfer efficiency that 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 between Pr3+ and Ca2+. In order to explore the approach for enhancing the Pr3+ concentration in CSS, we have tentatively added Mg2+ in Sc3+ site to compensate the residual positive charge caused by the substitution of Pr3+ for Ca2+ in CSS. Our results indicate that the addition of Mg2+ can not only increase Ce3+ concentration in CSS to make emission spectra move toward longer wavelength, but also promote Pr3+ incorporation into CSS lattices to enhance the Pr3+ emission. Finally, A white LED with CRI of 80, CCT of 8715 K and chromaticity coordinates of (0.28, 0.32) was fabricated by combining the single CSS: 0.05Ce3+, 0.01Pr3+, 0.3Mg2+ phosphor with a blue-emitting InGaN LED (450 nm) chip. However, this white LED needs more red emission component to be excellent 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 generate a yellow emission band around 574 nm (named Mn2+(I)) but also Sc3+ site to generate a red emission band around 680 nm (named Mn2+(II)). Through the efficient Ce3+→Mn2+ (Mn2+(I) and Mn2+(II)), Ce3+→Pr3+和Mn2+(I)→Pr3+ energy transfer, we have realized color tunable luminescence in the Ce3+, Pr3+ and Mn2+ co-activated CSS. With the enhancement of Mn2+ (Mn2+(I) and Mn2+(II)) emissions caused by the increasing Mn2+ nominal content, the red emission (around 610 nm) of Pr3+ also enhances. 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 with CRI of 90, CCT of 4980 K and chromaticity coordinates of (0.34, 0.31) is obtained by combining the single CSS: 0.08Ce3+, 0.01Pr3+, 0.3Mn2+, 0.2Mg2+ phosphor with a blue-emitting InGaN LED chip.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/41456
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	乔君. 钪硅酸盐白光LED荧光粉的研究[D]. 中国科学院大学,2014.

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