【作者】 冯仕华；

【导师】 翟永清；

【作者基本信息】 河北大学 ， 无机化学， 2010， 硕士

【摘要】 白光LED因其具有体积小、节能、环保、寿命长等优点而引起人们的广泛关注,被称为第四代照明光源。实现白光LED最成熟方式是荧光粉转换法,因此白光LED用荧光粉的制备和性能越来越受到人们的重视。稀土硅酸盐体系发光材料由于其化学稳定性好,耐水性强,发光颜色多样,应用广泛等特点,越来越引起人们的重视。本论文采用凝胶-燃烧法成功合成了稀土离子激活的系列白光LED用碱土金属多硅酸盐荧光粉,借助XRD、EDS、SEM、荧光光谱等现代测试手段,对合成产物进行了分析和表征,得出以下结论:1.采用凝胶-燃烧法成功合成了Eu2+掺杂的新型碱土多硅酸盐蓝色发光材料Sr2MgSi3O9:Eu2+,属四方晶系(Tetragonal)。其一次颗粒近似球形,粒径在100 nm左右。激发光谱分布在250~450 nm的波长范围,主激发峰位于424 nm处,次激发峰位于400 nm处,可以被InGaN管芯产生的近紫外辐射有效激发。发射光谱也为一宽带,最大发射峰位于470 nm附近,是典型的Eu2+的4f5d-4f跃迁导致的。Sr2MgSi3O9:Eu2+是一种很有前途用于白光LED的蓝色荧光粉。此外,探讨了Eu2+的掺杂浓度、还原温度及共掺杂离子等对材料发光亮度的影响。2.采用凝胶-燃烧法合成Ce3+、Tb3+共掺的新型发光材料Sr2MgSi3O9:Ce3+,Tb3+。该发光材料与Sr2MgSi2O7具有相似的晶体结构,同属四方晶系。样品一次颗粒近似球形,粒径在100 nm左右。Sr2MgSi3O9:Tb3+的激发光谱为一位于249 nm的宽带,发射光谱主要由473 nm,491nm,547 nm,585 nm等一系列发射峰组成,其中473 nm(5D3→7F3)为主发射峰,547 nm(5D4→7F5)为次发射峰;样品Sr1.955MgSi3O9:Tb3+0.04,Ce3+0.005的激发光谱由峰值分别249 nm和335 nm的双激发带组成,其中后者为主激发带。在335 nm激发下,其发射光谱由两部分组成,其中400 nm附近的带状发射对应于Ce3+的发射,而491 nm,547 nm,588 nm处的发射峰归属为Tb3+的5D4→7FJ(J = 6, 5, 4)跃迁发射,最强峰位于547 nm,对应Tb3+的5D4→7F5跃迁。此外,探讨了Ce3+掺杂量对样品发光亮度的影响,发现Ce3+可以把能量传递给Tb3+,对Tb3+起到敏化作用。3.采用凝胶-燃烧法合成Eu3+掺杂的新型碱土多硅酸盐红色发光材xSrO·MgO·ySiO2(x = 1~2,y = 2~3)。Sr2MgSi3O9:Eu3+和SrMgSi2O6:Eu3+的晶体结构均与Sr2MgSi2O7相似,同属四方晶系。其激发和发射光谱分析表明:激发光谱在220~300 nm之间出现一宽带吸收,归属于O2--Eu3+之间的电荷迁移带,300 nm以后出现的锐线峰为Eu3+的f-f跃迁吸收峰,其最强锐线峰位于400 nm,对应于Eu3+的基态到5L6激发态跃迁吸收。因此,荧光粉可以被InGaN管芯产生的紫外辐射有效激发。发射光谱由两个强发射峰组成,分别位于592 nm和618 nm处,分别属于典型的Eu3+的5D0→7F1和5D0→7F2跃迁。此外,探讨了发光中心Eu3+浓度、共掺杂离子Ti4+和Gd3+以及电荷补偿剂Li+,Na+,K+对样品发光特性的影响。4.采用凝胶-燃烧法合成Eu2+掺杂的碱土氯硅酸盐蓝色荧光粉Sr4Si3O8Cl4:Eu2+。该发光材料与Sr4Si3O8Cl4具有相同的晶体结构,属正交晶系。激发光谱分布在250~400 nm的一个较宽的波长范围,可以被InGaN管芯产生的紫外及近紫外辐射有效激发。在324 nm的紫外光激发下,Sr4Si3O8Cl4:Eu2+产生一个主峰位于484 nm的宽带发射,是典型的Eu2+的4f5d-4f跃迁导致的。通过在基质中掺杂Mg2+改变Eu2+的晶体场环境,使得Sr4-xMgxSi3O8Cl4:Eu2+发射光谱发生明显变化,当Mg2+浓度x从0增加到2.0时,发射主峰的位置由484 nm移到436 nm,即:发射光谱发生蓝移,发光颜色从蓝绿变为蓝色;激发主峰从324 nm移到343 nm,即激发光谱发生红移,故stokes位移减小,样品的发光效率提高。同时发现,当Mg2+掺杂浓度大于0.5时,样品的发光强度随着Mg2+浓度的增加而增大,蓝光发射增强。更多还原

【Abstract】 White light emitting diodes (LED) have attracted widespread interest due to their little volume, energy-saving, high efficiency, mercury pollution-free, long service life and so on, so it is honored to the fourth generation illuminating sources. The most mature method for achieving White LED is phosphor conversion. Therefore, more and more attention has been paid to the preparation and the properties of the phosphors for White LED.Alkaline earth polysilicate phosphors have more advantages on chemical stability, heat stability, excellent water resistance, varied luminescence color and wide application, so more attention is focused on this kind of phosphors.So in our present work, a series of alkaline earth polysilicate phosphors doped with rare earth ions for White LED were successfully synthesized by gel-combustion method. The as-synthesized phosphors were investigated by X-ray diffraction analysis (XRD), Energy Dispersive Spectrometer (EDS), Scanning Electron Microscope (SEM) and Fluorescence spectrophotometer. According to that, we get some valuable conclusions as follows:1. Eu2+ doped novel alkaline earth polysilicate blue emitting phosphors Sr2MgSi3O9:Eu2+ were synthesized by gel-combustion method. The phosphors possess the tetragonal crystal structure. The initial particles of the phosphors are nearly spherical in shape, and the grain size is about 100nm in diameter. The excitation spectrum of Sr2MgSi3O9:Eu 2+ is a broad band in the range of 250~450nm,the main peak is at 424nm and the secondary peak is at 400nm. So, the phosphors can be excited efficiently by UVLED chip with the near-UV radiation of 360~400 nm. The emission spectrum is also a broad band, and the emission peak is at about 470nm which is ascribed to Eu2+ ions typical transition from 4f5d to 4f. Sr2MgSi3O9:Eu2 + shows good prospect for blue phosphors of white LED. Moreover, the effects of the doping concentration of Eu2+, the sintering temperature and the co-doped ions on the luminescence properties of the phosphors have been discussed.2. Ce3+, Tb3+ co-doped novel phosphors Sr2MgSi3O9:Tb3+,Ce3+ were synthesized by gel-combustion method. Sr2MgSi3O9:Tb3+ and Sr2MgSi3O9:Tb3+,Ce3+ phosphors possess the similar tetragonal crystal structure as that of Sr2MgSi2O7. The initial particles of as-synthesized phosphors are nearly spherical in shape, and the particle size is about 100nm in diameter. The excitation spectrum of Sr2MgSi3O9:Tb3+ is a broad band and the main peak is at 249nm. The emission spectrum is composed of a series of peaks, located respectively at 473nm, 491nm, 547nm and 585nm. The main peak is at 473nm (5D3→7F3), and the secondary peak is at 547nm (5D4→7F5). The excitation spectrum of Sr1.955MgSi3O9:Tb3+0.04, Ce3+0.005 displays two broad bands with two peaks around 249nm and 335nm respectively; the latter peak is much stronger than the former. Under 335nm irradiation, the emission spectrum is composed of two parts. One part is a broad band at around 400nm, which belongs to the emission of Ce3+. The other part is composed of a series of peaks, located respectively at 491nm, 547nm and 588nm. These emission peaks are ascribed respectively to Tb3+ ions transition of 5D4→7FJ (J = 6, 5, 4) in Sr2MgSi3O9:Tb3+,Ce3+. The main emission peak is at 547nm (5D4→7F5). Moreover, the effect of Ce3+ doping amount on luminescent intensity was discussed. It is found that energy transfer from Ce3+ to Tb 3+ is efficient and sensitization lie in Ce3+ to Tb3+ in Sr2MgSi3O9 host under UV light.3. Eu3+ doped novel alkaline earth polysilicate red phosphors xSrO·MgO·ySiO2(x = 1~2,y = 2~3) were synthesized by gel-combustion method. The as-synthesized phosphors possess the similar tetragonal crystal structure as that of Sr2MgSi2O7. The excitation spectrum of samples presents wide band absorption between 220~300nm, which is ascribed to the charge transfer between Eu3+-O2-. The sharp peaks after 300nm belong to f-f transition of Eu3+, and the strongest sharp peak is located at 400nm. Therefore, samples can be efficiently excited by ultraviolet radiation from InGaN chip. The emission spectrum consists of two strong emission peaks at 592nm and 618nm, which are ascribed to 5D0→7F1 and 5D0→7F2 respectively. Moreover, the effect of the doping concentration of Eu3+, co-dope Gd3+ , Ti4+ and charge compensation agent Li+, Na+ and K+ on luminescent properties were discussed.4. Eu2+ doped the series of Sr4Si3O8Cl4:Eu2+ blue-green phosphors were synthesized by gel-combustion method. The as-synthesized phosphors have the same orthorhombic crystal structure as that of Sr4Si3O8Cl4. The excitation spectrum of Sr4Si3O8Cl4:Eu2+ is a broad band in the range of 250~400nm, and the main peak at 324nm, which can be excited efficiently by UV and NUV radiation generated by UVLED chip. Under the radiation of 324nm, the emission spectrum is also a broad band with the main emission peak at about 484nm. It’s ascribed to Eu2+ ions typical transition from 4f5d to 4f. Sr4Si3O8Cl4:Eu2+ shows good prospect for blue-green phosphors of white LED. It is found that doping Mg2+ ion in host leads to blue shift of the emission spectrum of Sr4-xMgxSi3O8Cl4: Eu2+. The reason is that doping Mg2+ ions change the crystal field of Eu2+. The main emission peak shifts from 484nm to 436nm when the concentration of Mg2+ changes from 0 to 2.0, the emitting colour varies from blue-green to blue; the main excitation peak shifts from 324nm to 343nm, so stokes shifts decrease, and luminous efficiency is improved. Moreover, it is found that the luminescent intensity increases with the increase of the concentration of Mg2+ when the concentration of Mg2+ is excess to 0.5, and blue emitting becomes strong.更多还原