Li掺杂ZnO纳米棒的导电和发光特性(英文)

利用气相输运方法,在(111)面硅衬底上制备了名义上原子数分数为2%的Li掺杂的ZnO纳米棒(样品A)。作为比较,我们在相同的生长条件下制备了没有任何掺杂的ZnO纳米棒(样品B)。XRD分析测试表明:样品A和样品B中的ZnO纳米棒具有纤锌矿六边形结构,没有其他氧化物,例如Li2O。Hall效应测量表明:样品A导电类型为p型,空穴载流子浓度为6.72×1016cm-3,空穴载流子迁移率为2.46 cm2.V-1.s-1。样品B为n型,电子载流子浓度为7.16×1018cm-3,电子载流子迁移率为4.73 cm2.V-1.s-1。低温光致发光光谱测试表明,样品A和样品B发光峰明显的区别是位于3.351 eV(样品B)和3.364 eV(样品A)处。根据文献报道,在没有掺杂的ZnO中,3.364 eV发光峰源于施主束缚激子发光。通过变温光致发光光谱的测试,证明了在样品A中,位于3.351 eV的发光峰源于受主束缚激子发光,其光学受主能级位于价带顶142meV处。     

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.     

SnO2纳米晶体的制备、结构与发光性质

使用软化学方法在碱性溶液中制备出了颗粒尺寸分布均匀的SnO2纳米颗粒,使用透射电子显微镜(TEM)、X射线衍射(XRD)、光致发光谱(PL)和光吸收谱等方法分析与表征了SnO2纳米颗粒的结构和光学性能.实验中通过表面活性剂的加入来控制纳米颗粒的结晶与凝聚.XRD,TEM的结果表明,原始制备出的SnO2纳米颗粒的平均粒径小于4 nm,为完好的晶体状态.纳米颗粒经过400-1000 ℃退火后晶粒尺寸进一步增大.光吸收谱表明,相对于体材料,纳米颗粒的禁带宽度展宽并随颗粒尺寸增大而红移.光致发光谱测试表明,不同温度下退火的SnO2纳米颗粒在350-750 nm有较强的发光,研究表明这是来源于颗粒表面的氧空位缺陷发光.     

SnO$lt;sub$gt;2$lt;/sub$gt;纳米晶体的制备、结构与发光性质

使用软化学方法在碱性溶液中制备出了颗粒尺寸分布均匀的SnO₂纳米颗粒,使用透射电子显微镜（TEM）、X射线衍射（XRD）、光致发光谱（PL）和光吸收谱等方法分析与表征了SnO₂纳米颗粒的结构和光学性能.实验中通过表面活性剂的加入来控制纳米颗粒的结晶与凝聚.XRD,TEM的结果表明,原始制备出的SnO₂纳米颗粒的平均粒径小于4 nm,为完好的晶体状态.纳米颗粒经过400—1000 ℃退火后晶粒尺寸进一步增大.光吸收谱表明,相对于体材料,纳米颗粒的禁带宽度展宽并随颗粒尺寸增大而红移.光致发光谱测试表明,不同温度下退火的SnO₂纳米颗粒在350—750 nm有较强的发光,研究表明这是来源于颗粒表面的氧空位缺陷发光. 关键词： 氧化锡 表面活性剂 纳米颗粒 光致发光     

纳米晶ZnO可见发射机制的研究

利用化学沉淀法制备了纳米ZnO粉体,室温下测量了样品的光致发光谱(PL)、X射线衍射谱(XRD),给出了样品的透射电子显微照片(TEM).X射线衍射(XRD)的结果表明:纳米晶ZnO具有六角纤锌矿晶体结构,颗粒呈球形或椭球形.观察到二个荧光发射带,中心波长分别位于398 nm的紫带和510 nm的绿光带.发现随退火温度升高,粒径增大,紫带的峰值减弱、绿带的峰值增强.证实了纳米晶ZnO绿光可见发射带来自氧空位形成的施主和锌空位形成的受主之间的复合.     

纳米锗颗粒镶嵌薄膜的荧光特性研究

研究了不同颗粒尺寸的纳米Ge-SiO₂镶嵌薄膜的室温荧光光谱以及不同激发光能量对荧光峰的影响．实验结果表明，沉积态Ge-SiO₂薄膜样品在可见光区域不发光．退火后的样品（平均锗颗粒尺寸为3.2—6.0nm）在380—520nm波长范围内有明显的蓝光发射现象．当用λ=300nm的光激发，观测到中心波长为420nm（2.95eV）的光致荧光峰；而用633nm波长的光激发，谱图上出现中心波长分别为420和470nm的两个荧光峰．随着纳米锗颗粒尺寸的增加，光致荧光峰的相 关键词：     

玻璃中CdSeS纳米晶体的室温光致发光谱

对掺有过饱和的镉、硒和少量硫的玻璃在500～800℃分别退火4h,生长了不同尺寸的CdSe_1-xS_x纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300～800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600～650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。     

氮化镓纳米粒子的制备及光致发光研究

采用直接氮化法制备出尺寸不同的GaN纳米粒子,分别利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）和光致发光（PL）谱测试手段对所制样品进行表征和发光特性的研究。结果表明：所制备的两种GaN纳米粒子直径分别为100 nm和300 nm左右。在GaN纳米粒子的PL谱中,中心在357 nm的发射源于本征发光,中心在385 nm的发射带源于浅施主能级到价带的辐射复合,中心在560 nm左右的发射带源于浅施主能级到深受主能级间的施主-受主对辐射发光。     

不同晶粒尺寸SnO2纳米粒子的拉曼光谱研究

对晶粒尺寸在4-80 nm范围的纯SnO2纳米颗粒进行了拉曼散射研究.除了SnO2 本征拉曼振动峰外,还有几个新的拉曼振动峰和波长在700 nm左右的一个发光很强而且峰宽很大的荧光峰被观察到.结果所示,当纳米颗粒尺寸减小时,纳米SnO2 颗粒的体相特征拉曼峰变弱,而由缺陷,表面和颗粒尺寸引起的相关效应呈强势.晶粒尺寸在20 nm左右是引起体相拉曼光谱变化的临界尺寸. 晶粒尺寸在20 nm以下,其体相拉曼峰的发生宽化和峰位移动, 以及分别出现在位于571 cm-1 的表面振动峰,位于351 cm-1 处的界面峰和与表面吸附水分子及氢氧基团的N系列拉曼峰是纳米SnO颗粒的主要特征.这些结果反映了纳米颗粒的微结构变化与颗粒尺寸和表面效应以及它们之间相互作用的信息.     

ZnO薄膜近带边紫外发光的研究

用ZnO陶瓷靶,采用脉冲激光沉积(PLD)技术在c-Al₂O₃衬底上制备了ZnO薄膜。通过不同温度下光致发光(PL)光谱的测量,对样品的紫外发光机理进行研究。 在较低温度(10 K)下的PL光谱中,观测到一个位于3.354 eV处的束缚激子(D⁰X)发射,随着温度的升高(~50 K),在D⁰X的高能侧观测到了自由激子的发射峰。在10 K温度下,3.309 eV处出现了一个较强的发光带A,此发光带强度随着温度升高先增大然后减小,并且一直延续到室温。重点讨论了此发光带的起源,并认为A带可归属于自由电子-受主之间的复合发射。     

Structural and photoluminescence properties of silicon nanocrystals embedded in SiC matrix prepared by magnetron sputtering

Si nanocrystals (NCs) embedded in an SiC matrix were prepared by the deposition of Si-rich Si_1?xC_x/SiC nanomultilayer films using magnetron sputtering, subsequently followed by thermal annealing in the range of 800～1200 °C. As the annealing temperature increases to 1000 °C, Si NCs begin to form and SiC NCs also start to emerge at the annealing temperature of 1200 °C. With the increase of annealing temperature, two photoluminescence (PL) peaks have an obvious redshift. The intensity of the low-energy PL peak around 669～742 nm gradually lowers, however the intensity of high-energy PL peak around 601～632 nm enhances. The low-energy PL peak might attribute to dangling bonds in amorphous Si (a-Si) sublayers, and the redshift of this peak might be related to the passivation of Si dangling bonds. Whereas the origin of the high-energy PL peak may be the emergence of Si NCs, the redshift of this peak correlates with the change in the size of Si NCs.     

Quantitative analysis of the phonon confinement effect in arbitrarily shaped Si nanocrystals decorated on Si nanowires and its correlation with the photoluminescence spectrum

Arrays of single‐crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) are grown by a metal‐assisted chemical etching process using silver (Ag) as the noble metal catalyst. The metal‐assisted chemical etching‐grown Si NWs exhibit strong photoluminescence (PL) emission in the visible and near infrared region at room temperature. Quantum confinement of carriers in the Si NCs is believed to be primarily responsible for the observed PL emission. Raman spectra of the Si NCs decorated on Si NWs exhibit a red shift and an asymmetric broadening of first‐order Raman peak as well as the other multi‐phonon modes when compared with that of the bulk Si. Quantitative analysis of confinement of phonons in the Si NCs is shown to account for the measured Raman peak shift and asymmetric broadening. To eliminate the laser heating effect on the phonon modes of the Si NWs/NCs, the Raman measurement was performed at extremely low laser power. Both the PL and Raman spectral analysis show a log‐normal distribution for the Si NCs, and our transmission electron microscopy results are fully consistent with the results of PL and Raman analyses. We calculate the size distribution of these Si NCs in terms of mean diameter (D₀) and skewness (σ) by correlating the PL spectra and Raman spectra of the as‐grown Si NCs decorated on Si NWs. Copyright © 2015 John Wiley & Sons, Ltd.     

Size-dependent intrinsic radiative decay rates of silicon nanocrystals at large confinement energies

We study ultrafast photoluminescence (PL) dynamics of Si nanocrystals (NCs). The early-time PL spectra (<1 ns), which show strong dependence on NC size, are attributed to emission involving NC quantized states. The PL spectra recorded for long delays (>10 ns) are almost independent of NC size and are likely due to surface-related recombination. Based on instantaneous PL intensities measured 2 ps after excitation, we determine intrinsic radiative rate constants for NCs of different sizes. These constants sharply increase for confinement energies greater than approximately 1 eV indicating a fast, exponential growth of the oscillator strength of zero-phonon, pseudodirect transitions.     

Mechanism and enhancement of photoluminescence from silicon nanocrystals implanted in SiO2 matrix

Photoluminescence (PL) spectra of Si nanocrystals (NCs) prepared by 130 keV Si ions implantation onto SiO2 matrix were investigated as a function of annealing temperature and implanted ion dose. PL spectra consist of two PL peaks, originated from smaller Si NCs due to quantum confinement effect (QCE) and the interface states located at the surface of larger Si NCs. The evolution of number of dangling bonds (DBs) on Si NCs was also investigated. For hydrogen-passivated samples, a monotonic increase in PL peak intensity with the dose of implanted Si ions up to 3×1017 ions /cm2 is observed. The number of DBs on individual Si NC, the interaction between DBs at the surface of neighbouring Si NCs and their effects on the efficiency of PL are discussed.     

Non-exponential decay kinetics: correct assessment and description illustrated by slow luminescence of Si nanostructures

The treatment of time-resolved (TR) photoluminescence (PL) decay kinetics is analysed in details and illustrated by experiments on semiconductor quantum dots, namely silicon nanocrystals (Si NCs). We consider the mono-, stretch- and multi-exponential as well as lognormal (LN) and some complex decay models for continuous and discrete distribution of rates (lifetimes). A particular attention is devoted to the thorough analysis of non-exponential decay kinetics. We explicitly show that a LN distribution of emitter sizes may results in LN distribution of decay rates. On the other hand, the distribution of rates cannot be, strictly speaking, Levy stable distribution (that results in the stretched-exponential decay). We introduce theoretical background and derive expressions to calculate the average decay lifetimes for some common decays with practical examples of their applications. Experimental aspects are discussed with special attention devoted to the major problems of the accurate TR PL data treatment, including background uncertainty, pulse duration, system response function etc. Finally, a thorough literature survey of TR PL in Si NCs is given. The methods and definitions outlined in this systematic review are applicable to various other material systems with slow decay like rare-earth and transition metal-doped materials, amorphous semiconductors, type-II heterostructures, singlet oxygen phosphorescence etc.     

Optical property investigation of SiGe nanocrystals formed by electrochemical anodization

We report on the optical property investigation of SiGe nanocrystals (NCs) prepared by electrochemical anodization (ECA) of SiGe layer grown by ultrahigh vacuum chemical vapor deposition (UHVCVD). At room temperature, SiGe NCs with higher Ge content demonstrate a redshift of the photoluminescence (PL) peak compared to Si NCs. It was found that the surface chemical composition, density, and the size of the SiGe NCs were very sensitive to the annealing conditions. Various spectroscopy measurements such as PL, FTIR, and XPS have been carried out to reveal the mechanism of the PL peak transition. The results indicated that the PL peak position was determined by two major factors, namely, interface state density and the size of SiGe NCs. It was shown that the higher the interface state density, the more significant the redshift of the peak position. While the smaller the size of the SiGe NCs, the more significant the quantum size effects become, resulting in the blueshift of the PL peak position.     

Modulation effect of microstructures in silicon-rich oxide matrix on photoluminescence from silicon nanoclusters prepared by different fabrication techniques

The modulation effect of microstructures on photoluminescence (PL) properties of silicon nanoclusters (Si NCs) in silicon-rich oxide (SRO) matrix prepared by electron-beam evaporation (EBE) and magnetron sputtering (MS) is investigated. A loose and porous microstructure is obtained from the SRO film prepared by EBE, while compact microstructure is acquired from that prepared by MS. The Si NCs with high density and good quality are formed in the SRO film prepared by EBE, and preferable PL performance of Si NCs is achieved in the EBE film with loose and porous microstructure. In contrast, the density and quality of Si NCs in the compact SRO film are suppressed and the PL properties are deteriorated due to the volumetric mismatching during the precipitation procedure of Si NCs. Optimization of the microstructures in SRO films should be made to reduce the volumetric mismatching and improve the PL properties of Si NCs.     

Blue–violet photoluminescence from colloidal suspension of nanocrystalline silicon in silicon oxide matrix

We report room temperature visible photoluminescence (PL), detectable by the unaided eye, from colloidal suspension of silicon nanocrystals (nc-Si) prepared by mechanical milling followed by chemical oxidation. The PL bands for samples prepared from Si wafer and Si powder peak at 3.11 and 2.93 eV respectively, under UV excitation, and exhibit a very fast (～ns) PL decay. Invasive oxidation during chemical treatment reduces the size of the nc-Si domains distributed within the amorphous SiO₂ matrix. It is proposed that defects at the interface between nc-Si and amorphous SiO₂ act as the potential emission centers. The origin of blue–violet PL is discussed in relation to the oxide related surface states, non-stoichiometric suboxides, surface species and other defect related states.     

Relative enhancement of photoluminescence intensity of passivated silicon nanocrystals in a silicon dioxide matrix

Photoluminescence (PL) intensity of passivated silicon nanocrystals (Si NCs) embedded in a SiO 2 matrix is compared with that of unpassivated Si NCs. We investigate the relative enhancement of PL intensity (I R ) as a function of annealing temperature and implanted Si ion dose. The I R increases simultaneously with the annealing temperature. This demonstrates an increase in the number of dangling bonds (DBs) with the degree of Si crystallization varying via the annealing temperature. The increase in I R with implanted Si ion dose is also observed. We believe that the near-field interaction between DBs and neighboring Si NCs is an additional factor that reduces the PL efficiency of unpassivated Si NCs.     

Photoluminescence polarization of semiconductor nanocrystals

We review the polarization properties of photoluminescence (PL) in nanocrystals (NCs) from both theoretical and experimental points of view. We show that, under linearly polarized excitation, NCs emit partly polarized light owing to their uniaxial structure or their anisotropic shape. In elongated NCs, the anisotropy may have two origins, the electronic confinement or the effect of depolarizing field created by the light-induced charges on the interfaces. Results of polarization studies in porous silicon are presented. They are explained by the shape of the Si NCs. Experiments in CdSe NCs reveal the fine structure of the excitonic levels and show evidence of the enhancement of the electron-hole exchange energy with decreasing NC size. Spin orientation in wurtzite-type NCs is achieved by optical pumping with circularly polarized light. The effect of a magnetic field on the degree of circular polarization and the mechanisms of spin relaxation are discussed. Results in large-size NCs are presented.