【作者】 吴作贵；

【导师】 张旭东；

【作者基本信息】 山东轻工业学院 ， 材料学， 2008， 硕士

【摘要】 掺铈钇铝石榴石（YAG:Ce）属于体心立方晶体,具有化学稳定性高、硬度大、高熔点、寿命长等优点;而且抗老化性能好,即使不包膜在潮湿或紫外线照射条件下也很稳定。因此,YAG:Ce是一种重要的荧光材料,广泛应用于阴极射线管屏幕及高分辨显示器等领域。而且YAG:Ce荧光粉与蓝光LED芯片组合能够混合成视觉上的白光,即白光LED。这种白光LED拥有广阔的应用前景,将成为能够替代白炽灯、荧光灯的第四代新型光源。本实验首先采用溶剂热法低成本制备了YAG纳米粉体。实验表明:合成过程中分散剂的添加量、沉淀剂的种类、溶液的浓度、pH值及保温时间对YAG粉体的性能均有影响。结果发现:适量（NH₄）₂SO₄的加入,可明显改善先驱沉淀物的分散性。当以尿素作为沉淀剂时得到的前驱体为碱式碳酸盐的混合物;而以碳酸氢铵为沉淀剂时前驱体主要为复合碳酸盐的混合物。保持反应物在适当pH值,以碳酸氢铵为沉淀剂的条件下,当盐溶液浓度较低时(Al³⁺浓度<0.2 mol/l),所得到的前驱体粉体在200℃保温5h的条件下即可合成平均晶粒尺寸为200nm,分散性好,且具有球形形貌的纯相YAG粉体;但是如果盐溶液浓度过高(Al³⁺浓度>0.5 mol/l)时,则需要在较长的保温时间才能得到单相YAG粉体,其主要是由于在沉淀过程中发生Y3+、Al³⁺的偏析及颗粒的团聚。在溶剂热反应时间过长的条件下,晶粒发生长大并产生团聚现象。在对YAG粉体合成工艺条件研究过程的基础上,采用乙二胺和水混合溶剂热法制备了YAG:Ce荧光粉。结果表明:将沉淀后的前驱沉淀物不经水洗、醇洗、干燥过程而直接溶剂热反应,在200℃保温5h的条件下即可合成具有球形形貌的纯相YAG:Ce荧光粉。荧光光谱分析表明,YAG:Ce荧光粉的激发光谱为双峰结构,在近紫外340nm处有一弱峰,最大激发峰在460nm附近,属于Ce³⁺的4f→5d特征跃迁。发射光谱是峰值在530nm的一宽带,对应Ce³⁺的5d→4f跃迁。而且当样品的发射峰为530nm时,发射光谱呈黄绿色,为一个宽带状光谱。因此发出的黄光能够很好的跟蓝光匹配混合形成视觉白光属于黄绿光。Ce³⁺在荧光粉中起激活剂的作用,且Ce³⁺的含量直接影响荧光粉的发光特性。本文通过对不同Ce³⁺掺杂浓度的荧光粉的发射光谱强度进行对比,确定了最佳的Ce³⁺掺杂浓度。在上述研究的基础上,我们探讨了溶剂热合成YAG:Ce的反应机理。研究结果表明,溶剂在超临界状态下加速了物质的传递,前驱物通过溶解-结晶反应,促进YAG:Ce晶核在较低温度下形成和长大,为进一步研究溶剂热法制备纳米粉体奠定了基础。更多还原

【Abstract】 Ce³⁺-doped yttrium aluminum garnet （YAG: Ce） belongs to the isometric crystal system, and has the merit of high chemical stability, high hardness, high melt point and long life et al. It has good weatherabiltiy and will be very stability even if in the circumstance of humid and ultraviolet without coated. So, YAG:Ce is the most important fluorescent materials, and has been used widely as ultra-short afterglow phosphors for cathode ray tubes and high-resolution displays. At the same time, the phosphors and blue LED chip can make up of optic white light, namely white LED. This white LED has wide application future and will become the forth new illuminant. Firstly, YAG nanoparticles were prepared by solvothermal method low costly. The effects of the mass of dispersion, precipitants, concentration of mother solutions, holding time on the formation of YAG and powder properties were investigated. The results show that the addition of appropriate amount of ammonium sulfate can obviously improve the dispersion. The precursors composes of metal hydroxides of carbonate using CO（NH2）2 as the precipitant. However, the precursors prepared are mainly compound of carbonate using NH4HCO3 as the precipitant. If the NH4HCO3 as the precipitant and proper pH value are adopted, pure-phase YAG with nano-sized, well-dispersed and spherical morphology can be obtained by heated at 200℃for 5h without any other intermediate phase with low metal ions concentration （[Al3+]<0.2mol/l）; but pure-phase YAG can not be synthesized with high metal ions concentration （[Al3+]>0.5mol/l）, which need longer holding time. This is mainly caused by the segregation of the precipitation Al3+ and Y3+ in the precursors and aggleration of particles. The synthesizing reaction for long time promotes the growth of grains and results in the agglomeration of grains.The simplified methods of synthesizing YAG:Ce phosphors are performed based on the study on synthesizs conditions of YAG powders. The results show that the pure-phase YAG:Ce with spherical morphology can be synthesized under 200℃for 5h as the precipitants without the processes of washing and drying. The excitation spectra of YAG:Ce phosphors have two peaks. The major one is around 460nm attributed to the 4f→5d transitions. Its emission band is wide with the peak at 530nm and it belongs to the 5d→4f transitions. Ce³⁺ ions act as the activation in the phosphors, they effect the luminescent properties of YAG:Ce phosphors. In this thesis, the best concentration of Ce³⁺ is made certain by comparing the emission spectra intensity of YAG:Ce phosphors with different Ce³⁺concentration.The formation mechanism of synthesized YAG:Ce phase was discussed on the basis of the research above. The findings indicated that YAG:Ce phase is directly formed by the dissolution/crystallization mechanism of precursor. This is due to the solution to reach the critical nucleation value for the YAG:Ce crystallites and promotes the formation of YAG:Ce grains at a much lower temperature than that of other methods. Some of the results are creative and useful, which is the important significance to prepare compounds under solvothermal conditions.更多还原