【作者】 焦海燕；

【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】 硅酸盐具有多种结构和稳定的物理、化学性能,很适合作为一类发光基质材料进行系统的研究。稀土掺杂的硅酸盐基质材料的发光性能,与近紫外区(NUV)的吸收带、电荷迁移带以及稀土元素的4f-5d跃迁和4f-4f跃迁密切相关。本论文以几种典型结构的硅酸盐作为基质材料并系统的考察稀土离子掺杂后其在NUV激发下的发光特性,特别是对荧光粉的晶体结构、掺杂、能量传递机制等理论研究,总结了稀土硅酸盐基荧光粉在NUV区域能被有效激发的关键条件和影响因素,对于NUV-LED用荧光粉的研究、推动LED荧光粉的商业化具有重要的理论意义及应用价值。本论文采用高温固相法合成了具有独特一维链状结构的Sr2Ce04:RE(RE=Sm3+; Ti4+,Eu3+;Eu3+,Sm3+)以及Ca2A12SiO7:RE(RE=Ce3+,Tb3+;Dy3+;Eu3+;Eu2+)、Sr2A12(Si, Mo)O7:Eu3+、CaSrAl2SiO7:Eu3+、CaAl2Si2O8:RE(RE=Eu;Eu2+,Mn2+;Ce3+,Tb3+)、BaMg2Si207:Eu2+,Mn2+、Mg2SiO4:RE(RE=Eu3+,Eu2+)和SrZrSi207:RE(RE=Ce3+,Tb3+,Eu3+,Dy3+)几类典型稀土硅酸盐荧光粉并考察了样品在NUV区域的发光特性。主要根据当前白光LED用荧光粉的发展需要,重点从新型高效红色荧光粉的开发和单一基质白光荧光粉的探索两个角度展开研究。结果表明：第一,对于稀土激活的一维链状结构的Sr2CeO4体系。1)合成了一种颜色可调谐的荧光粉Sr2CeO4：Sm3+,通过调节稀土离子Sm3+的掺杂浓度,可以调谐发光体的发光颜色。当Sm3+离子浓度较小(<3%)时,体系发出很强的白光；当Sm3+离子浓度较大(3%-15%)时,体系发出红光；其中,低浓度的荧光粉Sr2CeO4：1%Sm3+不仅有很强的发光强度,而且有优良的色纯度,色坐标为(0.334,0.320),与国际规定的标准白光值(0.33,0.33)很接近。2)Ti4+部分取代Ce4+后,荧光粉Sr2Ce1-xTixO4的激发光谱在300～380nm的吸收明显拓宽和增强,在334 nm激发下,掺杂Ti4+的荧光粉Sr2Ce0.99Ti0.01O4的发光强度是未掺杂Ti4+的荧光粉Sr2CeO4的85%；随后掺入Eu3+,得到的最佳红色荧光粉Sr1.95Ce0.99Ti0.01O4：0.05Eu3+的发光强度是未掺杂Ti4+的荧光粉Sr1.95CeO4：0.05Eu3+的1.5倍,积分强度是商用红粉Y2O2S：0.05Eu3+的3倍,其色纯度优良,色坐标为(0.665,0.33)。第二,单一基质白光荧光粉。本论文在BaMg2Si2O7：Eu2+,Mn2+：CaAl2Si2O8：Eu2+,Mn2+体系中,通过调节发光中心Eu2+,Mn2+的浓度并借助Eu2+→Mn2+能量传递,在这两类硅酸盐体系中得到了色度好,发光亮度高的单一基质白光荧光粉；并首次提出用除了Eu2+,Mn2+之外的双离子Ce3+,Tb3+掺杂来实现白光,证实在长波紫外光激发下Ca2Al2SiO7体系中存在Ce3+→Tb3+能量传递,通过Ce3+,Tb3+浓度的调节可以实现白光,是一种新型的双离子掺杂单一基质白光荧光粉；此外,在Ca2Al2SiO7基体中,通过掺杂单一离子Dy3+也实现了白光,在350nm激发下,发光强度最强的荧光粉是：Ca1.97Al2SiO7：0.07Dy3+,而色纯度最好的荧光粉是：Ca1.97Al2SiO7：0.01Dy3+,其色坐标为(0.340,0.338),相对色温为5164 K,可以作为一种很好的暖白光LED。第三,新型高效的红色荧光粉。本论文系统研究了Ca2Al2SiO7：Eu3+、Sr2Al2SiO7：Eu3+、CaSrAl2SiO7：Eu3+和Mg2SiO4：Eu3+荧光粉在NUV区域的发光性能,发现这几类荧光粉在393nm都有一个吸收峰,归属为Eu3+的特征吸收；在Ca2Al2SiO7和Sr2Al2SiO7体系中,393 nm处Eu3+的吸收峰相对于200～350 nm的O2-→Eu3+电荷转移跃迁吸收带较弱,通过Mo离子掺杂和电荷补偿离子Na+的引入不仅增强了荧光粉在～400 nm的吸收强度并提高了荧光粉的发光性能,最优的荧光粉Sr1.56Na0.22Eu0.22Al2Si0.98Mo0.02O7,其积分强度是商用红粉的1.5倍,色坐标为(0.659,0.331),比商用红粉更接近于NTSC的标准红光值(0.67,0.33),量子效率为50%,是一种很有潜力的NUV-LED用新型高效的红色荧光粉；在CaSrAl2SiO7体系中,Eu3+掺杂浓度x不同时,Eu3+占据的位置不同,当Eu3+的掺杂浓度x>0.14时,荧光粉在393nm的吸收峰较强,适合作为NUV-LED用红色荧光粉,其中最佳配比的红色荧光粉是Ca0.78SrAl2SiO7：0.22Eu3+,其色坐标为(0.650,0.350)；对于新型荧光粉Mg2SiO4：Eu3+,当Eu3+的掺杂浓度为0.09 mol时,其在393 nm处的跃迁吸收最强,色纯度优良,而且量子效率也较高,约为38%。第四,其它硅酸盐荧光粉。对于Ca2Al2SiO7：Eu2+体系的研究发现,随着Eu2+掺杂浓度的增加发射波长出现红移,并从晶体场角度解释了红移的原因；在空气气氛下用高温固相法合成的CaAl2Si2O8：Eu体系中观察到了Eu3+→Eu2+的自动还原现象,并利用电荷补偿模型解释了这种自动还原现象；在CaAl2Si2O8体系中,通过Ce3+,Tb3+双掺得到了一种适合NUV-LED的绿色荧光粉,其发光强度是单掺杂Tb3+荧光粉的10倍：对于Mg2SiO4：Eu2+和SrZrSi2O7：RE(RE=Ce3+,Tb3+,Eu3+)荧光粉的研究表明：在NUV区的吸收均很弱,因此都不适合作为NUV-LED荧光粉。更多还原

【Abstract】 Silicates are excellent hosts for photoluminescence (PL) materials for their various crystal structures and high physical-chemical stability. The luminescent properties of rare earth doped silicates are closely related to the NUV absorption band, charge transfer band, 4f-5d transition and 4f-4f transition, which are all of Rare-earth (RE) ions. In this thesis, the NUV PL properties of RE ions in several typical silicate hosts were systematically investigated. Our investigation is focused on the crystal structure, doping and the energy transfer mechanism of phosphor. We summed up the critical conditions and influencing factors about the rare-earth silicate-based phosphor, which have high-efficiently excited at NUV region. The results derived from the above research would contribute greatly to the developing of phosphors for NUV-LED and advance their application in LEDs.In this article, one-dimensional chains structure phsophor of Sr2Ce04:RE (RE= Sm3+, Ti4+/Eu3+, Eu3+/Sm3+) and several typical silicate phosphors of Ca2Al2Si07:RE (RE= Ce3+/Tb3+, Dy3+, Eu3+, Eu2+), Sr2Al2(Si, Mo)O7:Eu3+, CaSrAl2SiO7:Eu3+, CaAl2Si2O8:RE (RE= Eu, Eu2+/Mn2+, Ce3+/Tb3+), BaMg2Si207:Eu2+, Mn2+, Mg2Si04:RE (RE= Eu3+, Eu2+)、SrZrSi2O7::RE (RE= Ce3+, Tb3+, Eu3+, Dy3+) powder samples were synthesized by the solid-state reaction. Their luminescent properties under NUV excitation were investigated in detail. Based on the current demands about the development of white LED phosphors, our investigation is mainly focused on the exploitation of a new and efficient red phosphor and the exploration of a single matrix white phosphor. The results indicate that:1. A system of rare earth doped phsophor Sr2Ce04 with one-dimensional chains structure1) A tunable full color emitting phosphor Sr2Ce04:Sm3+ was synthesized. Its emission color could be changed by tuning concentration of rare-earth activator Sm3+. The doped compound emits strong white light when the concentration of the doped Sm3+ is low (<3%), When the Sm3+ concentration is increased (3%-15%), it emits red light. Among all the samples, Sr2CeO4:1%Sm3+ phosphor show not only strong emission intensity but also good color purity, its chromaticity coordinates is (0.334,0.320), which is more close to the the NTSC standard values (0.33,0.33). 2) By doping small amount of Ti4+ into Ce4+ sites, the excitation intensity of charge transfer (CT) band of 300-380 nm was significantly broaden and enhanced. As a result, under 334nm excitation, compared with the undoped phosphor Sr2CeO4, the emission intensity of phosphor Sr2Ce1-xTixO4 has improved about 85% by doping 0.01mol Ti4+. When doping Eu3+ ion, the optimum phosphor Sri.95Ceo.99Ti0.01O4:0.05Eu3+ with the integrated intensity 3 times higher than that of the red commercial phosphor Y2O2S:0.05Eu3+, and owns excellent color purity with chromaticity coordinates of (0.665,0.33).2. A single matrix white phosphor. By adjusting the concentration of luminous center Eu2+, Mn2+, and with the energy transfer of Eu2→Mn2+, we obtained a single matrix white phosphor with good color purity and high brightness in two types of silicate system BaMg2Si207:Eu2+,Mn2+ and CaAl2Si20g:Eu2+,Mn2+. We first report a novel rare earth activated a single matrix white phosphor CaaAl2SiO7:Ce3+, Tb3+, and demonstrated that energy transfer from Ce3+ to Tb3+ in Ca2Al2SiO7 results in a white emission activated with long-UV radiation. Moreover, we prepared a single ion activated white phosphor Ca2Al2SiO7:Dy3+, under 350 nm excitation, the phosphor Ca1.97Al2SiO7:0.07Dy3+ exhibits the strongest emission intensity and the phosphor Ca1.97Al2SiO7:0.01Dy3+ owns excellent color purity with chromaticity coordinates of (0.340,0.338) and relative color temperature of 5164 K. These results show that the phosphor Ca2Al2SiOy:Dy3+ can be considered as a potential warm white light phosphor for application in LEDs.3. A new and efficient red phosphor. Photoluminescence properties of Ca2Al2SiO7:Eu3+, Sr2Al2SiO7:Eu3+, CaSrAl2SiO7:Eu3+ and Mg2Si04:Eu3+ were evaluated under NUV excitation. It is found that there existed an absorption peak in 393 nm, which was assigned to the absorption of Eu3+. In Ca2Al2SiO7:Eu3+ and Sr2Al2SiO7:Eu3+, compared with the CTB absorption of O2-→Eu3+ in the 200-350 nm, the intensity of 393 nm absorption peak is weaker. By introducing Mo ion and charge compensator ion Na, but also strengthen the absorption of the phosphors at-400 nm and strongly enhanced the emission intensity of Eu3+ under 393 nm excitations. The intense red-emitting phosphor is Sr1.56Euo.22Na0.22Al2Si0.9gMo0.02O7 with the integrated intensity 1.5 times higher than that of the red commercial phosphor. Its chromaticity coordinates of (0.659,0.331) is more close to the NTSC standard values (0.67,0.33) than that of the red commercial phosphor and the quantum efficiency of Sr1.56Eu0.22Na0.22Al2Si0.98Mo0.02O7 is 50%. These results indicate that this novel red phosphor could be considered as a promising red phosphor for application in LEDs. In CaSrAl2SiO7:Eu3+ system, optical properties were studied as a function of Eu3+ concentration x, when x>14%, the intensity of absorption of the f-f transitions of Eu3+ at 393 nm is stronger than that of the broad charge transfer transition band (CTB) around 250 nm, and which is matches well with the output lights of NUV-LED. As a result, the optimum red phosphor is Ca0.78SrAl2Si07:0.22Eu3+ with the chromaticity coordinates of (0.650,0.350). The possibility of Mg2Si04:Eu3+ as novel promising NUV red phosphors were exploited. The results indicate that the optimum concentration of Eu3+ is 0.09 mol while the intensity of absorption at 393 nm is the strongest and its quantum efficiency is around 38%.4. Other Silicate phosphors. The Eu2+ doped Ca2Al2SiO7 system exhibited a redshift in its emission wavelength, and explaied the reason of red shift from the crystal field. CaAl2Si2O8:Eu was prepared in air atmosphere by the solid state reaction. It was found that a reduction of Eu3+to Eu2+ in CaAl2Si2O8 in air condition. And the reduction mechanism from Eu3+ to Eu2+ in this compound has been discussed from the charge compensation model. In CaAl2Si2O8:Ce3+, Tb3+ system, CaAl2Si2O8:Ce3+, Tb3+phosphor with the emission intensity 10 times higher than that of the green phosphor CaAl2Si2O8:Tb3+ phosphor. The result indicated that CaAl2Si2O8:Ce3+, Tb3+would be a potential NUV-LED green phosphor. Moreover, the NUV photoluminescence properties of Mg2SiO4:Eu2+ and SrZrSi2O7:RE (RE = Ce3+, Tb3+, Eu3+) were investigated in detail. The result indicated that Mg2SiO4:Eu2+ and SrZrSi2O7:RE (RE= Ce3+, Tb3+, Eu3+) are not suitable for NUV-LED phosphor because the absorption of these phosphors in NUV region are very weak.更多还原