【作者】 蒋自强；

【导师】 王育华；

【作者基本信息】 兰州大学 ， 材料物理与化学， 2010， 博士

【摘要】 本论文对比典型的硅酸盐发光材料基质,制备了主要以Ce3+离子激活的三类锗酸盐基质发光材料,研究了它们在近紫外或者蓝光激发下的发光特性,并考察了其作为相应的白光LED用荧光粉的潜力。工作之一：利用高温固相法制备了石榴石结构的Mg3Y2Ge3O12,并研究了Si掺杂对Mg3Y2Ge3O12: Ce3+发光特性的影响。Mg3Y2Ge3O12: Ce3+在380-520 nm范围内有较强的吸收,在460 nm激发下,可以发射出波长范围在480-750 nm,峰值在573 nm的黄光。在Mg3Y2Ge3O12基质中掺入Si后,由于Si的半径小于Ge,导致立方晶格发生扭曲,Ce3+离子5d轨道分裂程度增加,因此,源于Ce3+离子最低的5d能级至4f基态能级的跃迁发射发生了明显红移。当系列样品Mg3Y1.94(Ge1-xSix)3O12:0.06Ce3+中Si的掺杂量x从0增加至0.7时,样品的发射峰值从575 nm红移至604 nm。此外,通过测试系列掺杂Si的Mg3Y2Ge3O12基质样品的漫反射光谱,发现基质的带隙值随着Si的掺杂量的提高而变大。当Si的掺杂量x从0增加至0.7时,基质带隙宽化了约0.5 eV。基质带隙变宽使Ce3+离子光致电离几率降低,从而大幅提高了Mg3Y2Ge3O12:Ce3+的发光量子效率。由于Si掺杂引起发射光谱的红移和量子效率显著提高,使得Mg3Y2(Ge, Si)3O12:Ce3+成为一种潜在的蓝光芯片激发的暖白光LED用荧光粉。工作之二：利用高温固相法制备出了主要以Ce3+离子激活的正锗酸盐Ca2GeO4, CaMgGeO4, Sr2GeO4和Ba2GeO4,并研究了其发光特性。首先利用CASTEP程序分别计算了Ca2GeO4和CaMgGeO4的电子能带结构以及态密度。Ca2GeO4和CaMgGeO4都具有橄榄石结构,两者均为间接带隙半导体,带隙值分别为4.0和4.16 eV。两种基质的导带底都主要由Ca的3d轨道构成,而价带顶主要由O的2p轨道构成。Ca2GeO4:Ce3+的激发范围在380-520 nm,峰值位于467nm。其发射光谱为范围在480-750 nm的形状不对称的宽带,峰值位于565 nm,相比于YAG:Ce荧光粉有明显的红移,是潜在的蓝光芯片激发的LED用黄色发光材料。CaMgGeO4:Ce3+在蓝光区域同样有很好的吸收,但是在该波段激发下没有观察到任何可见光发射。在Ca2GeO4:Ce3+体系中掺入适量的Al3+取代Ge4+,可以起到电荷补偿作用,从而提高Ca2GeO4:Ce3+的发光强度。在Ca2GeO4:Ce3+体系中掺入Mn2+离子,随着Mn2+离子浓度的增大,Ca2GeO4:Ce3+, Mn2+的发射峰值从565 nm红移至600 nm半峰宽则从140 nm变窄至78 nm,并且强度也急剧减弱。Sr2Ge04:Ce3+和Ba2Ge04:Ce3+的最强激发位置分别为367 nm和344 nm。在350 nm激发下,两者的发射都呈现为370-520nm的宽带,峰值都位于413 nm左右,色坐标比商用的近紫外LED蓝色荧光粉BAM偏紫,并且量子效率分别只有35.2%和28.3%。因此,虽然Sr2Ge04:Ce3+和Ba2Ge04:Ce3+在近紫外区域有良好的吸收,但是其作为近紫外LED蓝光材料的潜力不大。工作之三：利用高温固相法制备了Sr2Al2Ge07单相和Ce3+、Eu2+、Pr3+、Tb3+离子单掺杂以及Ce3+/Pr3+、Ce3+/Tb3+共掺杂的Sr2Al2GeO7样品,并研究了其发光特性。Rietveld全谱拟合结果得出Sr2Al2GeO7属四方晶系,P42(?)m空间群,晶胞参数分别为a=7.947(1)A和c=5.361(4)A。CASTEP程序计算结果表明Sr2Al2GeO7为间接带隙半导体,带隙值为4.38 eV。其导带底主要由Sr的5p轨道构成而价带顶主要由O的2p轨道构成。Sr2Al2GeO7:Ce3+的有效激发位于330-400 nm,在363 nm激发下,其发射为主峰位于430 nm的宽带。Sr2Al2GeO7:Eu2+在240-480 nm有较强的吸收,但是在室温下没有观察到在相应波段激发下的可见光发射。Sr2Al2GeO7:Pr3+的发射光谱由峰值分别位于485、530、563、616和647 nm的一系列发射峰组成。Sr2Al2GeO7:Tb3+则发射出一组峰值分别位于489、542、589和619 nm的发射峰。共掺杂Ce3+、Pr3+离子的样品,由于Ce3+、Pr3+离子之间未能发生有效的能量传递作用,因此未能实现近紫外光激发下的白光发射。而共掺杂Ce3+、Tb3+离子的样品,由于Ce3+-Tb3+的能量传递作用,在Sr2Al2GeO7中同时观察到了Ce3+和Tb3+离子的发射,并且通过控制激活剂离子的掺杂浓度,在名义组成为Sr1.9625Al2GeO7:0.0075Ce3+,0.03Tb3+的样品中实现了色坐标为(0.25,0.29)的白光发射。更多还原

【Abstract】 A series of Ce3+doped Mg3Y2Ge3O12 garnet phosphors were synthesized by solid-state reaction method and their luminescence properties were studied. Mg3Y2Ge3O12:Ce3+ absorbs in the wavelength range of 380-520 nm. Under 460 nm excitation, Mg3Y2Ge3O12:Ce3+shows a yellow emission band in the wavelength range of 480-750 nm with the maximum intensity appearing at 575 nm. When a part of Ge in the Mg3Y2Ge3O12 host is replaced by Si, the crystal field splitting between the two lowest 5d level of Ce3+is enhanced which could be due to a smaller Ce3+-O2-bond length, as result, the emission peak of the Mg3Y2Ge3O12:Ce3+is redshifted from 575 nm to 604 nm when 70%of Ge is replaced by Si. Further more, Doping Si into the host lattice remarkably broaden the band-gap of the Mg3Y2Ge3O12, which makes the Ce3+photoionization difficult, as a result, the quantum efficiency and the emission intensity of the Mg3Y2Ge3O12:Ce3+phosphor is greatly enhanced. The enhanced yellow-to-orange emission of Si-doped Mg3Y2Ge3O12:Ce3+makes it a potential conversion phosphor for warm white light-emitting diodes.Ce3+activated alkaline earth germanates Ca2GeO4, CaMgGeO4, Sr2Ge04 and Ba2GeO4 were synthesized by solid-state reaction method and their luminscence properties were studied. The electronic structure of Ca2GeO4 and CaMgGeO4 were calculated using the CASTEP code. Ca2GeO4 and CaMgGeO4 are olivine structure mineral, they both show indirect optical band-gap with band-gap energy of about 4.0 eV and 4.16 eV respectively. The top of their valence band are dominated by O 2p states, while the bottom of their conduction band are mainly composed of Ca 3d and Ge 4s states. The excitation band of Ca2GeO4:Ce3+ranges from 380 to 520 nm with a maximum intensity appearing at about 465 nm. Under 465 nm excitation, Ca2GeO4:Ce3+exhibits a broad yellow emission band in the wavelength range of 480-750 nm with the maximum intensity appearing at 565 nm. The emission of Ca2GeO4:Ce3+shows an obvious redshift when compared to the YAG:Ce phosphor, which makes it an potential white LED conversion phosphor. CaMgGeO4:Ce3+shows excellent absorption in the blue region as well, however, no visible emission is observed when the phosphor is excited under the blue light. Doping Al3+to replace a part of Ge4+in the Ca2GeO4:Ce3+could significantly enhance its emission intensity, which could be due to the charge compensation effect. When Mn2+is codoped into Ca2Ge04:Ce3+, the emission peak of Ca2Ge04:Ce3+, Mn2+shifts from 565 nm to 600 nm, and the bandwidth is reduced from 140 nm to 75 nm when the concentration of Mn2+increase. The excitation peak of Sr2GeO4:Ce3+and Ba2GeO4:Ce3+are 367 nm and 344 nm respectively. Under 350 nm excitation, they both exhibit an emission band in the wavelength range of 370-520 nm. Compared with commercial blue LED phosphor BAM, their chromaticity coordinates get close to the purple region. Moreover, the quantum efficiency of Sr2GeO4:Ce3+and Ba2GeO4:Ce3+are measured to be 35.2% and 28.3% respectively. Thus, although Sr2Ge04:Ce3+and Ba2GeO4:Ce3+have efficient absorption in the near-UV region, they are not proper to serve as blue LED phosphors.Single phase of Sr2Al2Ge07 and Ce3+, Eu2+, Pr3+, Tb3+doped as well as Ce3+/Pr3+, Ce3+/Tb3+codoped Sr2Al2Ge07 were synthesized by solid-state reaction method. The Rietveld refinement of the Sr2Al2GeO7 powder sample was carried out using GSAS program. Sr2Al2Ge07 crystallizes as a tetragonal structure with space group P42(?)m and lattice constants of a=7.947(1) A and c=5.361(4) A。Its electronic structure was calculated using the CASTEP code. S2Al2GeO7 shows an indirect optical band-gap with band-gap energy of about 4.38 eV. The top of the valence band is dominated by O 2p states, while the bottom of the conduction band is mainly composed of Sr 5p states. The efficient excitation band of Sr2Al2Ge07:Ce3+is in the wavelength range of 330-400 nm. Under 363 nm excitation, it shows an emission band in the wavelength range of 380-510 nm with a maximum at 430 nm. Sr2Al2GeO7:Eu2+shows efficient absorption in the wavelength range of 240-480 nm, but there is no visible emission is observed when the phosphor is excited under the related wavelength range. The emission of Sr2Al2GeO7:Pr3+is composed of several emission lines peaking around 485,530,563,616 and 647 nm respectively. The emission spectrum of Sr2Al2GeO7:Tb3+is composed of a group of emission peaking at 489,542,589 and 619 nm. For the Ce3+/Tb3+codoped Sr2Al2Ge07 phosphors, because of the energy transfer process from Ce3+to Tb3+, both the blue emission of Ce3+and the yellowish green emission of Tb3+are obtained. Combining the two emissions whose intensity is adjusted by changing the doping level of the coactivator, an optimized white light with chromaticity coordinates of (0.25,0.29) is generated. The phosphor could be a potential white phosphor for near-UV LEDs.更多还原