稀土掺杂氧化物纳米发光材料研究

综述了稀土掺杂纳米发光材料方面的研究进展;主要介绍稀土掺杂氧化物纳米晶与体相材料相比所具有的一些特有的光谱学性质,包括光谱的移动与谱线的展宽、4fN电子的跃迁与弛豫过程、表面局域环境和格位对称性、电子-声子耦合、能量传递、浓度猝灭、温度猝灭以及光诱导发光强度变化等光谱现象,同时也探寻了其中的物理实质。主要对上转换纳米发光材料和一维纳米线/管的发光性质进行了介绍。     

GaAs/AlGaAs超晶格的光致发光

在室温下测量了GaAs/A l0.3Ga0.7As超晶格的光致发光,发现在波长λ=761 nm处存在一较强的发光光峰,此发光峰目前尚未见报道。经理论分析表明,此峰是量子阱中的第一激发态电子与受主空穴复合发光。实验还观测到在λ=786 nm处,λ=798 nm处和λ=824 nm处分别存在一发光峰,分析表明λ=786 nm处的发光峰为量子阱阱中费米能级附近的电子与轻空穴复合发光;λ=798 nm处的发光峰为量子阱内的基态电子到轻空穴的复合发光;λ=824 nm处的发光峰为阱中激子复合复合发光。理论计算与实验结果符合的很好。     

射频磁控共溅射GaAs/SiO2纳米颗粒镶嵌薄膜的光学性质

应用射频磁控共溅射方法和真空退火方法制备了GaAsSiO2纳米颗粒镶嵌薄膜.X射线衍射实验结果表明,经高温退火的薄膜中形成了面心立方闪锌矿结构的GaAs纳米晶粒,晶粒平均直径为1.5—3.2nm.吸收光谱展示了由于强量子限域引起的1.5—2eV的吸收边蓝移.室温光致荧光(PL)光谱显示了电子重空穴激子与电子劈裂空穴激子的近紫外和紫外双PL谱峰以及深俘获态的PL谱峰.对实验吸收边蓝移量与有效质量模型的蓝移量的悬殊差别、俘获态PL谱的形成以及PL谱线的特征作了解释.应用激光Z扫描技术测量了退火温度为500℃的复合膜在非共振条件下的光学非线性,结果表明,复合膜的非线性折射率系数和非线性吸收系数都比块材GaAs相应的系数增大了5个数量级.光学非线性系数增大主要起因于强量子限域效应 关键词： 射频磁控共溅射 GaAsSiO2纳米颗粒镶嵌薄膜 光谱 激光Z扫描     

MEH-PPV/ZnO纳米晶无机有机复合电致发光器件的研究

以Ⅱ一Ⅵ族无机半导体ZnO纳米颗粒为电子传输层,MEH-PPV为空穴传输层兼发光层,得到的电致发光器件比单层MEH-PPV器件的发光亮度和效率都明显提高。器件结构为ITO／MEH-PPV／ZnO／Al的电致发光光谱同单层PPV器件的光谱出现了不同,在620nm处出现了一个小的发光峰,应该是ZnO的发光。另外,双层结构器件的启亮电压由单层器件的9V降到了4V左右。由I-V曲线及发光光谱可判断出发光区域应在MEH-PPV／ZnO界面处,并且复合区域可能随着电压的变化而变化。     

SrS∶Eu,Sm光存储机理的研究

采用高温固相反应法在还原气氛下制备了SrS:Eu,Sm样品,利用荧光光谱仪测量了这种光存储材料的激发光谱和发射光谱.将样品用紫外灯(265 nm)照射激发饱和后,再用980 nm的红外激光器激励,利用荧光光谱仪测试得到了峰值位于599 nm的光激励发光光谱.此外还利用热释光谱仪测试了样品的热释光谱.探讨了SrS:Eu,Sm的光存储机理,认为引入的稀土离子在SrS的带隙中形成分裂能级.当用紫外光照射材料时,Eu的电子从基态被激发到激发态或基质材料的导带,其中一部分电子被辅助激活剂Sm的陷阱俘获,实现信息写入.当材料被与陷阱深度相当的红外光激励时,电子陷阱Sm2 俘获的电子才可能跃出俘获能级,与空穴在Eu的激发态和基态能级上复合,多余的能量以可见光的形式释放出来,实现信息读出.     

Sm~(3+)掺杂对SrLaGa_3O_7自身长余辉发光性质的影响

采用高温固相法制备了Sr La Ga_3O_7∶x Sm~(3+)长余辉材料,通过XRD、荧光光谱、热释光谱分别对样品的结构以及发光性能进行了研究,探究了Sm~(3+)掺杂浓度对样品自身长余辉发光性能的影响。研究结果表明:样品在254 nm紫外光照射后,Sr La Ga_3O_7∶x Sm~(3+)在386 nm有明显的长余辉发光,可持续60 min,主要是由于样品中空位引起的发光。随着掺杂Sm~(3+)浓度的增加,样品的发射光谱和余辉强度先增强后减弱,并出现明显的红移现象,这与Sm~(3+)掺杂所造成的空位浓度密切相关。当Sm~(3+)的摩尔分数达到0.5%时,样品在420 nm处展现最佳的长余辉性质。热释光谱表明掺杂后的样品中存在两种不同的陷阱,分别是由氧空位和锶空位引起的,这两种陷阱不仅影响样品的发光强度,而且充当俘获中心从而影响样品的余辉性能。     

纳米ZnO镶嵌SiO2薄膜的磁控溅射制备和发光性质的研究

采用射频磁控反应溅射方法在SiO衬底上制备了纳米ZnO镶嵌SiO2薄膜.在室温下利用吸收光谱和光致发光光谱研究了样品的光学性质.发现吸收光谱随纳米ZnO尺寸的减小发生了明显的蓝移,表明随着ZnO尺寸的减小,量子尺寸效应增强,导致带隙展宽,吸收峰蓝移.光致发光光谱在387和441 nm附近出现了两个发光带,分析认为紫外发光来源于自由激子的辐射复合,而蓝色发光带来自于氧空位的电子到价带的跃迁,并用时间分辨光谱和发光衰减证实了上述观点.     

电子俘获光存储材料BaLiF3:Eu2+的光激励发光及光存储性质研究

利用高温固相反应法制备了混晶状的BaLiF3:Eu2 样品.其紫外光激发的发射峰与光激励发光峰均在410 nm处,属于Eu2 的5d-4f跃迁发光.光激励峰位于660 nm,因而可以配用简单廉价的氦氖激光器.根据光谱特征给出了光激励发光的简单机理.测量了该材料光激励发光衰减性能,结果表明BaLiF3:Eu2 存储的信息可以方便地擦除掉.该材料具有优良的光激励发光特性,是一类很有发展前途的电子俘获光存储材料.     

纳米介孔ZrO2及其表面修饰的发光性质

水热合成法制备的高度有序多孔ZrO2具有规则六角排列、均匀纳米孔洞(约1．8nm)，并且其蓝、(近)紫外光发射强度比纳米微晶材料高2个数量级。本文研究了纳米介孔ZrO2这种不同于常规体材料与纳米晶材料的特殊发光性质。通过化学方法对纳米介孔ZrO2进行表面修饰后，能进一步提高其光发射聋度约3倍。通过这些发光性质的研究，以期增进对ZrO2发光机理的认识。     

ZnO纳米棒的拉曼和发光光谱研究(英文)

本文对采用湿化学方法合成的ZnO纳米棒样品的拉曼光谱和发光光谱进行了研究。由扫描电镜结果可知,合成的ZnO纳米棒具有很好的尺寸发布均匀性,直径在30 nm左右,长度大于1微米。采用显微拉曼光谱技术,得到了632.8 nm波长激发的拉曼光谱,并和体相样品的拉曼光谱进行了对比分析;由325 nm激光波长激发得到的荧光光谱可知样品具有很好的紫外发光性质。     

PbWO4闪烁晶体的发光动力学模型

在对PbWO₄闪烁晶体的光谱特性、发光衰减及其温度依赖以及热释光的研究基础上,并结合理论计算,提出了PbWO₄晶体发光的动力学模型,给出了PbWO₄晶体的基本能带结构及激子发光中心能态、陷阱能级在能隙中的位置。用此模型可以完整说明PbWO₄的发光过程,特别是导致室温下发光效率低的原因。最后还对其主发射成分蓝、绿发光中心的起源作了简要讨论。     

纳米ZnO薄膜可见发射机制研究

利用溶胶－凝胶法 （Sol-Gel）制备了纳米ZnO薄膜，获得了高强的近紫外发射室温下测量了样品的光致发光谱(PL )、吸收谱(ABS)、X射线衍射谱(XRD).X射线衍射(XRD)的结果表明：纳米ZnO薄膜呈多晶态，具有六角纤锌矿结构和良好的C轴取向；发现随退火温度升高，（002）衍射峰强度显著增强，衍射峰的半高宽（FWHM）减小、纳米颗粒的粒径增大.由吸收谱(ABS)给出了样品室温下带隙宽度为3.30 eV.在PL谱中观察到二个荧光发射带，一个是中心波长位于392 nm附近强而尖的紫带，另一个是519 nm附近弱而宽的绿带研究了不同退火温度样品的光致发光峰值强度的变化关系，发现随退火温度升高，紫带峰值强度增强、绿带峰值强度减弱，均近似呈线性变化.证实了纳米ZnO薄膜绿光发射主要来自氧空位(Vo)形成的浅施主能级与锌空位(VZn)形成的浅受主能级之间的复合，或氧空位(Vo)形成的深施主能级上的电子至价带顶的跃迁；紫带来自于导带中的电子与价带中的空位形成的激子复合.     

Photoluminescence of ZnO films prepared by r.f. sputtering on different substrates

Polycrystalline ZnO films with good orientation were deposited on sapphire, quartz, Si and 7059 glass substrates by r.f. magnetron sputtering. A strong UV photoluminescence (PL) peak (located at 356 nm) and a weak blue emission peak (located at 446 nm) were observed at room temperature (RT) for the films deposited on sapphire, quartz and Si substrates when excited with 270 nm light. For the films prepared on Corning 7059 glass, only a strong 446 nm blue emission peak was found, and the PL intensity decreased with increasing oxygen pressure during films deposition. The intensity of the UV emission increased 7 and 14 times, respectively, for the films on sapphire and quartz substrates after high temperature annealing in vacuum. The UV emission originates from the inter-band transition of electrons and the blue emission is due to transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.     

Role of Ti 3d carriers in mediating the ferromagnetism of Co∶TiO2 anatase thin films

We study the surface and bulk electronic structure of the room-temperature ferromagnet Co∶TiO(2) anatase films using soft- and hard-x-ray photoemission spectroscopy with probe sensitivities of ～1 and ～10 nm, respectively. We obtain direct evidence of metallic Ti(3+) states in the bulk, which get suppressed to give a surface semiconductor, thus indicating the difference in electronic structure between surface and bulk. X-ray absorption and resonant photoemission spectroscopy reveal Ti(3+) electrons at the Fermi level (E(F)) and high-spin Co(2+) electrons occurring away from E(F). The results show the importance of the charge neutrality condition: Co(2+)+V(O)(2-)+2Ti(4+)?Co(2+)+2Ti(3+) (V(O) is oxygen vacancy), which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals.     

纳米ZnO薄膜的光致发光性质

利用溶胶－凝胶法制备了纳米ZnO薄膜,室温下测量了样品的光致发光谱(PL)、吸收谱(ABS)、X射线衍射谱(XRD)．X射线衍射(XRD)的结果表明：纳米ZnO薄膜呈多晶状态,具有六角纤锌矿晶体结构和良好的C轴取向．观察到二个荧光发射带,中心波长分别位于395 nm的紫带、524 nm的绿带和450 nm附近的蓝带．证实了纳米ZnO薄膜绿光可见发射带来自氧空位(VO)形成的浅施主能级和锌空位(VZn)形成的浅受主能级之间的复合;450 nm附近的蓝带来自电子从VO的浅施主能级到价带顶或锌填隙(Zni) 到价带顶或导带底到VZn的浅受主能级的复合．     

Emission spectra of KBr:Sn2+

Crystals of KBr:Sn²⁺ irradiated in the A₁, A₂, B or D absorption bands exhibit strong emission in the region of 500 nm. The dependence of this emission on excitation wavelength in the A absorption band shows the 500 nm emission band to be a doublet. This doublet structure is due to electrostatic perturbation from a nearby cation vacancy. It is not possible from emission spectra alone to decide on the actual symmetry of the A_T1 and A_T2 centres responsible for the emission doublet but the various possibilities are discussed. Quenching experiments show that a small emission band at 700 nm is due to Sn²⁺ dimer centres. A series of weak emission bands on the high-energy side of the A_T band are ascribed to emission from the relaxed excited B and D states.     

Electromigration with enhanced green emission in the titanium dioxide nanotube/graphene composite

One of the most studied photoluminescence emission peaks of anatase titanium dioxide (TiO₂) is green, located at about 520 nm, which is assigned to the radiative recombination between a mobile electron in the conduction band and oxygen vacancy defect as a trapped hole in the bandgap. Composite materials of TiO₂ with graphene are normally shown by the gradual quenching of photoluminescence intensity as a result of carrier lifetime extension, which is important to enhance photocatalytic activity. Herein we report an observation of the intensity enhancement of the green PL emission in a composite TiO₂ nanotube (TNT) and graphene produced through facile hydrothermal synthesis. The heterojunction formation of graphene and TNT makes the excited photoelectrons easy to diffuse from TNT to graphene. Hence, the recombination rate of mobile electrons in graphene and trapped holes located on the nanotube surface is enhanced due to the high mobility of electrons in graphene.     

Study on the defects of ZnO nanowire

The room-temperature photoluminescence property of ZnO nanowires was studied. It showed an ultraviolet peak and a visible light band in the PL spectrum. Through Gaussian fitting, it was found that the visible light band can be divided into two peaks at 2.37 eV and 2.53 eV, which was originated from oxygen antisite and oxygen vacancy defects, respectively. After being exposed to air or post-annealed in oxygen ambience, aging effect was observed and the peak at 2.53 eV disappeared due to the removal of oxygen vacancy defects. Therefore, it is suggested that oxygen antisite and oxygen vacancy coexist in ZnO and induce visible light emission.     

Electronic properties of anatase TiO2 doped by lanthanides: A DFT+U study

The effects of mono-doping of 4f lanthanides with and without oxygen vacancy defect on the electronic structures of anatase TiO₂ have been studied by first-principles calculations with DFT+U (DFT with Hubbard U correction) to treat the strong correlation of Ti 3d electrons and lanthanides 4f electrons. Our results revealed that dopant Ce is easy to incorporate into the TiO₂ host by substituting Ti due to its lower substitutional energy (∼−2.0 eV), but the band gap of the system almost keeps intact after doping. The Ce 4f states are located at the bottom of conduction band, which mainly originates from Ti 3d states. The magnetic moment of doped Ce disappears due to electron transfer from Ce to the nearest O atoms. For Pr and Gd doping, their substitutional energies are similar and close to zero, indicating that both of them may also incorporate into the TiO₂ host. For Pr doping, some 4f spin-down states are located next to the bottom of the conduction band and narrow the band gap of the doping system. However, for Gd doping, the 4f states are located in deep valence band and there is no intermediate band in the band gap. The magnetic moment of dopant Gd is close to the value of isolated Gd atom (∼7 μB), indicating no overlapping between Gd 4f with other orbitals. For Eu, it is hard to incorporate into the TiO₂ host due to its very higher substitutional energy. The results also indicated that oxygen vacancy defect may enhance the adsorption of the visible light in Ln-doped TiO₂ system.     

γ射线辐照与O2退火对Bi∶CdWO4单晶体光谱性能的影响

用500和800℃,在氧气下,对掺Bi钨酸镉晶体进行热退火处理,测定了处理后晶体的吸收光谱与发射光谱。随退火处理温度的升高晶体的吸收强度降低,吸收边带发生蓝移。在373与980nm的光激发下,分别观察到发光中心为528nm的CdWO4晶体本征发光与发光中心为1 078nm的Bi 5+发光。晶体样品通过高温氧气处理,发光中心为528nm的荧光带强度增强,但发光中心为1 078nm的荧光带强度变弱。这可能是由于氧退火使Bi 5+转化成Bi 3+所致。经退火处理后,晶体的颜色逐渐变浅,透光率明显提高,这是由于晶体中氧空位减少所致。经γ射线辐照处理后,528nm处的发光增强,而1 078nm处的发光减弱,这可能是由于γ射线辐照后导致Bi 5+变成Bi 3+。