【作者】 蒋继峰；

【导师】 洪樟连；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2008， 硕士

【摘要】 为了应对全球日益加剧的能源危机和环境污染问题，“节能”和“绿色”成为材料科学领域的主要研究攻关目标之一。白光LED照明技术因其具有“节能”、“环保”、“高效”和“长寿命”等特点，被称为继白炽灯、节能灯之后的新一代绿色环保的照明光源，是涉及材料、电子、信息等学科领域的热点。本文在综述白光LED照明技术发展状况基础上，结合白光LED用黄色YAG：Ce³⁺荧光粉理化性质、光谱特性、制备方法、专利技术保护等的研发现状，提出采用不同工艺途径制备YAG：Ce³⁺荧光粉并进行工艺、结构、性能的对比分析与关联研究，以期为探索发展新型实用化技术提供理论支持的研究构想。论文采用XRD、FT-IR、DTA／TG、PL、SEM等测试手段，对经固相反应法、共沉淀法、溶胶-凝胶法三种工艺制备的YAG：Ce³⁺荧光粉样品的材料特性与发光性能进行了表征；在此基础上，对比分析了不同制备工艺的荧光粉在合成温度、物相形成规律、材料微结构形貌与发光性能等方面的异同；根据相关结果提出了具有继续研究价值、可望开发出具有自主知识产权的YAG：Ce³⁺荧光粉的制备工艺。此外，针对YAG：Ce³⁺荧光粉红光部分发射不足导致荧光转换型白光LED显色指数不足主要的问题，开展了采用Pr³⁺离子来增强红光部分的发射，通过共沉淀法制备了YAG：Ce³⁺，Pr³⁺荧光粉的研究。采用固相反应制备YAG：Ce³⁺荧光粉，并重点研究了助熔剂对YAG：Ce³⁺的合成温度、发光性能与颗粒形貌等方面的影响。研究发现，助熔剂可降低YAG相的转变温度、提高发光性能、加快晶粒生长。不同工艺对YAG相合成温度、物相结晶发育状态，组织结构与颗粒形貌，以及发光强度有显著的影响。固相反应法YAG相合成温度较高，加入助熔剂后需1300℃煅烧才能转变为YAG相，而且转变过程需经过Y₄Al₂O₉（YAM）相、YAlO₃（YAP）相等中间相。采用共沉淀法与溶胶-凝胶法制备YAG：Ce³⁺荧光粉的结果表明，湿化学法工艺可显著降低纯YAG相的合成温度。共沉淀法900℃热处理的产物已完全转变为YAG相，而且没有任何中间相的产生；产物为平均粒径35 nm左右；用溶胶-凝胶法800℃热处理即可得到YAG为主晶相的产物，900℃得到了平均粒径在30-40 nm之间的纳米YAG：Ce³⁺荧光粉。三种工艺制备的YAG：Ce³⁺荧光粉的激发光谱和发射光谱的形状相似。激发谱由位于344与470 nm左右的两个激发峰构成，分别对应于Ce³⁺的²F_5／2→5D的跃迁及²F_7／2→5D的跃迁，位于蓝光的470 nm是激发主峰。用此蓝光激发，荧光粉均发出主峰在535-545 nm之间，范围覆盖500-700 nm的宽带黄光发射。研究表明，不同工艺合成的荧光粉的发光强度都随反应温度升高而增强，但在同一温度下发光强度有很大的不同。经1400℃煅烧后，溶胶-凝胶法制备样品的发光强度最低，而共沉淀法与加有固熔剂固相反应法合成样品的发光强度都较好。分析认为，荧光粉发光强度主要是受发光基质相组成及晶粒生长发育情况的影响，而这两因素又主要受制备工艺及热处理温度的影响，Ce³⁺只有在YAG相中才具有较好的发光性能。1400℃时共沉淀法与加有助熔剂固相反应法制备的YAG：Ce³⁺荧光粉具有晶粒生长较好，晶体结构完整，因此发光性能也较好。综合考虑合成温度及发光强度，我们认为共沉淀法与加有助熔剂固相反应法制备的YAG：Ce³⁺荧光粉具有晶体结构完整、发光性能良好等优点，是制备实用化荧光粉的优选技术途径。如果从合成温度和晶相控制两方面考虑，共沉淀法最有研究和发展价值。在以上研究基础上，采用了YAG相合成温度低、发光强度高的共沉淀法合成了Ce³⁺、Pr³⁺共掺离子的YAG：Ce³⁺，Pr³⁺荧光粉。结果表明，在470 nm蓝光激发下，YAG：Ce³⁺，Pr³⁺的发射光谱除Ce³⁺的发射峰外，在610 nm及640 nm处还出现Pr³⁺的发射峰，分别对应于Pr³⁺的¹D₂→³H₄跃迁及³P₀→³H₅跃迁。Pr³⁺的发射增强了红光部分的发射，相应的色坐标也向右下方移动，有利于提高白光LED的显色指数。研究发现，当Pr³⁺的掺杂浓度达到0．015时，Pr³⁺发光强度最大，继续增加Pr³⁺浓度，Pr³⁺和Ce³⁺发光反而减弱。更多还原

【Abstract】 In order to deal with the global energy crisisi and environment pollution,research and development for environmental-friendly and energy efficient materialshas been the main goal for materials science scientists. Because of its energyefficiency, environmental friendness, high luminance efficiency and long life, theLED lamp has been considered the new generation light to replace the classicalincandescent lamp and fluorescent lamp.In this thesis, based on development of white-LEDs and YAG:Ce³⁺ phosphor’sphysical and chemical property, luminescent property and preparation methods, weproposed that comparison and relation among preparation route, structure andluminescence properties of YAG:Ce³⁺ phosphors prepared with different synthesismethods, were studied in order to develop new applicable synthesis method forYAG:Ce³⁺ phosphors.XRD、FT-IR、SEM and PL spectra were used to characterize the as-preparedphosphors which were prepared by different methods of solid-state reaction,co-precipitation method and sol-gel methods. Their aspects of synthesis temperature,crystal growth and morphology and luminescent property were compared andstudied. Considering the relative low white-LED’s color rendering index asYAG:Ce³⁺ phosphor’s lacks the red emission, the Pr³⁺ co-doped YAG:Ce³⁺,Pr³⁺phosphors were prepared by co-precipitation method in order to enhance the redemission and improve the color rendering index for white-LED’s.The effects of flux on synthetic temperatures, luminescent properties andmorphologies of YAG:Ce³⁺ phosphors prepared by solid state reaction were studied.Results showed that flux could lower the formation temperature of YAG phase,improve luminescent intensity and accelerate the crystal growth. The formationtemperature of YAG phase, crystal growth status, microstructure and luminescentintensity of YAG:Ce³⁺ phosphors depend on preparation methods. It was found thatthe synthetic temperature of pure YAG phase was as high as 1300℃even if the fluxwas added in solid-state reaction. It was verified that the final YAG phase must betransformed from intermediate phase of YAM and YAP.For the wet-chemistry method, the synthetic temperature for pure phaseYAG:Ce³⁺ phosphors needs only 800℃-900℃in the co-precipitation and sol-gelmethods. In addition, the precursors prepared by co-precipitation method transformdirectly to crystalline YAG phase from its amorphous structure without anyintermediate phases which is obviously different from the case in solid-statereaction.. The nano-sized YAG:Ce³⁺ phosphors were obtained with an average particle size at about 35 nm through both sol-gel method and co-precipitationmethod.It was found that YAG:Ce³⁺ phosphors prepared by three different methodshave similar excitation and emission spectra. The excitation spectrum was composedof two peaks at 344 and 470 ran, respectively, which are due to the ²F_5/2→5D and²F_7/2→5D transitions of Ce³⁺ ion. The main peak of excitation was 470 nm which isin the range of blue light. Under blue light excitation, the YAG:Ce³⁺ phosphors emityellow light centered at 535-545 nm with broad band range from 500 to 700 nm.It was revealed that the emission intensity of phosphors increases withincreasing reaction temperature. Obvious difference of luminescence intensity wasfound among phosphors prepared at same reaction temperature by different method .The products prepared by sol-gel method have the poorest luminescent properties,and that prepared by co-precipitation and flux-aid solid-state reaction had goodluminescent intensity. The content of host phase of YAG and its growth status areconsidered two key factors determining the luminescent intensity. The Ce³⁺ ions donot emit in YAM and YAP phases while it has excellent luminescent property inYAG phase.It was found that co-precipitation method and flux-aid solid-state reaction weretwo routes to synthesize phosphors with practical value, because their products havegood crystal growth of crystalline and morphology and excellent luminescentproperty. Moreover, the co-precipitation method maybe the best way to prepareYAG:Ce³⁺ phosphors when synthetic temperature and phase control were taken intoaccount.YAG:Ce³⁺,Pr³⁺ phosphors with low synthsis temperature and high luminescenceintensity were successfully synthesized by co-precipitation method. It was found that,besides the emission band of Ce³⁺, the emission spectrum of YAG:Ce³⁺,Pr³⁺ has twoadditional sharp peaks at 610 and 640 nm which correspond to ¹D₂→³H₄ transitionand ¹D₂→³H₄ transition of Pr³⁺ ion, respectively. The red emission from Pr³⁺ ioncould improve the CIE of white-LEDs using YAG:Ce³⁺,Pr³⁺ phosphors. Also, it wasfound that Pr³⁺ ions had the strongest emission intensity with doping concentrationof 1.5 mol%, which is considered to be the best doping level because theluminescent intensity decreased at high Pr³⁺ doping concentration above 1.5 mol%.更多还原