白光LED用新型Ce:YAG系列荧光晶体的生长及光学光电性能研究

发布时间：2019-05-23 12:38

【摘要】：商用白光LED是由蓝光In Ga N芯片和Ce:YAG荧光粉封装在一起制成的,荧光粉混合于环氧树脂/硅胶中并涂覆于芯片上。然而由于环氧树脂/硅胶导热性和化学稳定性较差,在高功率芯片照射或者较高温度使用环境下容易发生老化、黄化,造成LED色偏进而严重缩短器件的使用寿命。另外,由于红光成分的缺乏,此类LED器件往往呈现出较高的色温和较低的显色指数。研究表明,与荧光粉相比,Ce:YAG荧光晶体呈现出更加优异的光学性能和更高的热稳定性能。因此,本论文提出通过提拉法生长出高质量Ce:YAG单晶材料来替代传统的商用荧光粉,并通过在Ce:YAG晶体中共掺杂稀土离子/过度金属离子Tb,Mn,Eu等来增加发射光中的红光成分,从而改善白光LED的相关光学性能。提拉法生长得到高质量的Ce:YAG,Ce,Tb:YAG,Ce,Mn:YAG,Ce,Mn,Tb:YAG及Ce,Eu:YAG 5种晶体。采用X射线粉末衍射技术(XRD),SEM/STEM,吸收(UV-vis)和荧光光谱(PL),变温光谱,寿命衰减,X射线精细结构谱(EXAFS),电子顺磁共振谱(EPR),光电性能测试等手段对这五种晶体的光学性能进行了详细的分析研究。主要研究内容及结果如下:1、X射线粉末衍射(XRD)结果表明,稀土离子Tb,Eu和过渡金属离子Mn的掺杂会导致YAG晶胞体积产生轻微的改变,但并不影响YAG晶体的晶相结构。2、吸收光谱表明,Ce:YAG,Ce,Tb:YAG,Ce,Mn:YAG,Ce,Mn,Tb:YAG及Ce,Eu:YAG这5种晶体除了在发光中心460nm处均有着强烈的吸收(对应于Ce~(3+)的4f→5d轨道的跃迁吸收)外,同时也出现了掺杂离子Tb,Mn,Eu的特征吸收峰,在460nm蓝光激发下,5种晶体的发射光谱可由中心波长约530nm(5d~(1 2)E_gГ8_g→4f~(1 2)F_(7/2)Г_(8u))的500nm~650nm宽带发射峰组成,其中Ce,Mn:YAG和Ce,Mn,Tb:YAG晶体样品的发射光谱中均出现了567nm的宽带发射峰(Mn~(2+)的~4T_1→~6A_1的轨道跃迁),一定程度上弥补了红光成分的缺失。3、研究了Ce,Mn,Tb:YAG晶体的在303K-563K温度范围内的变温光谱,结果表明,与商用荧光粉相比,随着温度的升高,单晶呈现出更小的光损失,具有更高的热稳定性。4、研究了Ce,Mn:YAG的X射线精细结构谱(EXAFS)和电子顺磁共振谱(EPR),结果表明掺杂的Mn离子的价态主要以+2价为主。5、测试了5种晶体与460 nm蓝光芯片封装而成的白光LED的光电参数,探讨了掺杂离子的种类、晶片厚度、支架、AB胶、驱动电流等对晶片发光性能的影响。结果表明,Tb离子的掺入能一定程度上降低白光LED的色温,但显色指数较低;Mn离子的掺入能够提高白光LED的显色指数,降低色温;Eu的掺入对Ce~(3+)的发光有淬灭作用。6、研究了Ce,Mn:YAG单晶片的H_2退火工艺,结果表明,合适温度下的退火能够消除晶体生长和加工中产生的缺陷和应力,一定程度上的提高了晶片的发光性能。
[Abstract]:Commercial white LED is made of blue In Ga N chip and Ce:YAG fluorescent powder. The phosphor is mixed in epoxy resin / silica gel and coated on the chip. However, due to the poor thermal conductivity and chemical stability of epoxy resin / silica gel, it is easy to aging and yellowing in the environment of high power chip irradiation or high temperature, resulting in LED color deviation and seriously shortening the service life of the device. In addition, due to the lack of red light composition, this kind of LED devices often show higher color temperature and lower color index. The results show that compared with the fluorescent powder, Ce:YAG fluorescence crystal has better optical properties and higher thermal stability. Therefore, in this paper, high quality Ce:YAG single crystal materials are grown by Czochralski method to replace the traditional commercial phosphors, and rare earth ions / excessive metal ions Tb,Mn, are co-doped in Ce:YAG crystals. Eu et al., etc., to increase the red light composition in the emitted light, so as to improve the related optical properties of white light LED. High quality Ce:YAG,Ce,Tb:YAG,Ce,Mn:YAG,Ce,Mn,Tb:YAG and Ce,Eu:YAG crystals were obtained by Czochralski method. X-ray powder diffraction technique (XRD), SEM/STEM, absorption (UV-vis) and fluorescence spectrum (PL), variable temperature spectrum, lifetime decay, X-ray fine structure spectrum (EXAFS), electron parammagnetic resonance spectrum (EPR), The optical properties of these five crystals were analyzed and studied in detail by means of photoelectric performance test. The main research contents and results are as follows: 1. X-ray powder diffraction (XRD) results show that the doping of rare earth ion Tb,Eu and transition metal ion Mn can lead to a slight change in the cell volume of YAG. However, the crystal phase structure of YAG crystal is not affected. 2, the absorption spectra show that Ce:YAG,Ce,Tb:YAG,Ce,Mn:YAG,Ce,Mn,Tb:YAG and Ce, The five crystals of Eu:YAG not only have strong absorption at the luminous center 460nm (corresponding to the transition absorption of 4f 鈮，

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