面向功率型白光LED的复合结构荧光陶瓷光谱调制及光提取效率提升研究

Light Emitting Diodes (LEDs) are attracting much attention its long life time, high efficiency, environmental friendly property (mercury-free). It becomes a promising candidate to replace the incandescent lamps and the fluorescent lamps in the lighting industry. .At present, the typical technology for white light generation is the so called phosphor converted (PC) white LEDs, which uses the combination of a blue LED chip and the Ce:YAG powder phosphors dispersed in the organic matrix, like resin or silica gel. The proper proportional mixture of blue light emitted by the chip and the yellow emission of phosphor excited by the blue light generates white light. However, problems still exist. The heat resistance of the organic matrix is not good. For high power LED chips, the junction temperature increases rapidly during operation. Serious deterioration and degradation of the organic matix will occur. In addition, the aging problems of organic matrix also induces a colour change, which also deteriorates the LEDs`s performance. .Turning the Ce:YAG powders into transparent ceramics might be an effective solution to the above mentioned problems. Thus, Ce:YAG phosphors do need to be dispersed in organic matrix. So a stable performance can be expected for high power white LEDs. The advantadges of ceramics also lie in its easy fabrication, easy shaping, etc. .However, still there are some problems to be solved for Ce:YAG ceramic phosphors. First, due to the lackage of the red emission, the color temperture is about 6000 K, which is too high than that of the warm-white light. And the color rendering index is about 80~90 for the LUXEONTM white LED based on the Ce:YAG ceramic phosphor technology by Philips LumiLeds. In this project, we propose a composite structure ceramic phosphor to improve the color temperature and the color rendering index of Ce:YAG ceramic phosphors. The upper layer is the Ce:YAG yellow transparent ceramic phosphor, while the lower layer is the Ce, Pr:YAG or Ce, Cr:YAG red transparent ceramic phosphor. Under the ~460 nm excitation of the GaInN blue LED chip, the red emission generated by the red ceramic phosphor layer can pass through the Ce:YAG layer without being absorbed. The intensity of the red, yellow, blue emission can be ajusted independently, so the color temperature and the color rendering index can be improved. .In addition, since Ce:YAG has high refractive index, we propose a patterned upper surface of the Ce:YAG ceramic layer for higher light extraction efficiency and better heat removal, which is of great significance to high power LEDs.

用Ce:YAG陶瓷做为白光LED荧光材料可解决将Ce:YAG荧光粉分散于树脂、硅胶等有机材料中所产生的不利散射、色温一致性差、有机材料老化、着色等问题。然而，Ce:YAG荧光陶瓷仍存在由其荧光光谱缺少红光成分而导致色温偏高、显色指数不理想等问题。本课题创新提出复合结构透明荧光陶瓷来改善色温和显色指数，具体为：上层为Ce:YAG黄光荧光陶瓷，下层为Ce,Pr:YAG或Ce,Cr:YAG红光荧光陶瓷，下层红光荧光陶瓷在GaInN蓝光芯片激发下发出的红光可不被吸收而透过Ce:YAG透明荧光陶瓷，上层的Ce:YAG荧光陶瓷在蓝光激发下发出黄光，适当比例红、黄荧光与GaInN芯片的蓝光混合得色温与显色指数改善的白光，由于蓝、黄、红光的强度可以独立调节，所以不影响Ce:YAG的高荧光量子效率。本课题还将利用陶瓷材料易于成型的特点，在陶瓷出光表面引入图形阵列，与蓝光芯片结合，以提高光提取效率，改善散热。

背景.设计、研究与开发抗老化甚至无老化、低光衰、高荧光产额、色温可调的全无机荧光材料是高功率白光LED的重要发展方向之一，近年来得到了国内外著名研究机构及公司的高度关注，其在发光物理等基础研究领域及高功率白光LED等技术领域均具有重要意义。.主要研究内容.本项目经2013年1月至2015年12月三年间的研究，按照预定计划对以下几个方面进行了系统研究。.1. 对双层复合结构Ce:YAG基荧光陶瓷的制备，具体包括组分设计、成型、烧结等；2. 荧光陶瓷的发光性能、具体包括荧光发射温度依赖特性、激活离子间的能量转移机理、与蓝光LED结合所获得白光的流明效率等；3. 提高荧光陶瓷的荧光提取效率，具体为通过在荧光陶瓷出光表面引入图形结构；设计并制备Ce:YAG+Al2O3、Ce:YAG+MgAl2O4等复相荧光陶瓷, 利用复相荧光陶瓷中2~5.3 μm尺度Al2O3、MgAl2O4相高折射率晶粒的散射作用，提高荧光陶瓷中由GaInN LED芯片入射的蓝光及Ce:YAG晶粒黄光发射的光提取效率。.重要结果.基于以上研究进展，发票SCI收录科技论文6篇，申请中国发明专利5项，获得授权1项中国发明专利；参加国际会议（第13届欧洲陶瓷学会国际会议）1人次,并做分会口头报告一篇；协助培养硕士研究生（已毕业）和博士研究生（在读）各一名。.关键数据.实现了0.1at%Ce:YAG/0.1at%Ce,0.3at%Cr:YAG双层复合结构荧光陶瓷76 lm/W的白光荧光发射，其在1 W蓝光LED激发下获得了为4329 K低色温白光输出（相同条件下采用0.5at%Ce:YAG陶瓷的色温为7083 K）；Ce:YAG+Al2O3、Ce:YAG+MgAl2O4复相荧光陶瓷在1 W蓝光LED激发下所获得的复合白光输出分别获得了95 lm/W和99 lm/W的流明效率。.科学意义. 本项目的研究工作及相关成果对稀土离子发光领域施主-受主间的能量转移机理研究具有参考价值；并在高功率白光LED的色温调节及光提取效率提升等领域的材料设计及制备思路上具有创新性和启示性。