多种ZnO纳米结构和ZnO/ZnS核壳结构的制备

以Zn(NO3)2.6H2O和CO(NH2)2为原料,采用均匀沉淀法,制备出了棒状、花状、球状纳米氧化锌(ZnO)。将ZnO微球体分散在Na2S溶液中,通过离子替代法,成功制备了ZnO/ZnS核壳结构。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)等测试手段对ZnO纳米结构和ZnO/ZnS核壳结构的晶体结构和表面形貌进行了表征,初步探讨了纳米ZnO和ZnO/ZnS核壳结构的生长机理。根据测试结果得知,ZnO纳米棒呈现六方纤锌矿结构,随着Zn2+浓度逐渐增加,ZnO纳米结构形貌由单分散的棒状聚集成花状,最后演变成球形。ZnO/ZnS复合结构为内核ZnO,外面包覆一层ZnS的核壳结构。所有的纳米ZnO均具有相似的发光特点,ZnO/ZnS核壳结构的发光性能有了很大的改善。     

The UV and blue light emission properties of Mn doped ZnO nanocrystals

We present a study of the light emission properties over wavelengths from UV to blue of Mn doped ZnO nanocrystals fabricated by means of a thermal evaporation vapor phase deposition process. The samples were grown with a Mn mole ratio in the Zn/Mn mixed source of 0% (pure ZnO sample, used as a reference), 5%, 10%, or 15% in a constant O₂/Ar gas mixture flowing at 500 °C. The pure ZnO nanocrystals exhibited a strong and predominantly UV emission peaking at 377 nm. In the photoluminescence spectra of mixed ZnO:Mn nanocrystals the major UV emission shifts from 377 to 408 nm, and a strong blue emission appears at 435 nm. The former is mainly induced by the impurity levels of Mn introduced in the band gap of the ZnO nanocrystals, while the latter is closely related to defect and Mn²⁺ ions. With increasing Mn concentration the blue emission is enhanced due to the strong exchange interaction in the short range spin system and the excess impurities on the surface. The results show that the optical properties of ZnO can be tuned by the doping concentration of Mn. Mn doped ZnO nanocrystals with strong blue emission can be used in the fabrication of blue light devices.     

ZnO/ZnS核/壳纳米结构的形态及其演变模式

用两步生长的方法在醋酸锌和六亚甲基四胺水溶液中生长ZnO纳米棒阵列,然后以ZnO纳米棒阵列为模板,在Na2S水溶液中硫化0.5～6 h形成ZnO/ZnS纳米结构.用XRD,SEM和TEM表征了ZnO/ZnS核/壳纳米结构的晶体结构、表面形貌.研究了ZnO/ZnS核/壳纳米结构的形态及其转变的模式.在硫化过程中,ZnO首先形成ZnO/ZnS核/壳纳米棒,随着硫化程度的增强,核/壳结构顶部出现空洞,空洞扩展形成管状结构,进一步硫化,管状结构坍塌.硫化形成的ZnO/ZnS结构的形态不仅依赖于初始纳米棒的直径大小和硫化时间的长短,还依赖于纳米棒的分布密度.     

Role of Interface Chemistry in Opening New Radiative Pathways in InP/CdSe Giant Quantum Dots with Blinking‐Suppressed Two‐Color Emission

InP/CdSe core/thick‐shell “giant” quantum dots (gQDs) that exhibit blinking‐suppressed two‐color excitonic emission have been synthesized and optically characterized. These type II heterostructures exhibit photoluminescence from both a charge‐separated, near‐infrared type II excitonic state, and a shell‐localized visible‐color excitonic state. Infrared emission is intrinsic to the type II QD, while visible emission can either be eliminated or enhanced through chemical modification of the InP surface prior to CdSe shell growth. Single‐QD photoluminescence measurements confirm that the dual color emission is from individual nanocrystals. The probability of observing dual emission from individual QDs and the extent of blinking suppression increases with shell thickness. Visible emission can be stabilized by the addition of a second shell of CdS, where the resulting InP/CdSe/CdS core/shell/shell nanocrystals afford the strongest blinking suppression, determined by analysis of the Mandel Q parameter. Transient absorption spectroscopy verifies that dual emission arises when hole relaxation from the shell to the core is impeded, possibly as a result of enhanced interfacial hole trapping at F^? or O^2? defect sites. Electron–hole recombination in the shell then competes with slower type II recombination, providing a different mechanism for breaking Kasha's rule and allowing two colors of light to be emitted from one nanostructure.     

The optical properties of rare earth Gd doped ZnO nanocrystals

We present a study of the light emission properties, from UV to blue spectral region, of Gd doped ZnO nanocrystals fabricated by means of a thermal evaporation vapor phase deposition process. The samples were grown from a mixed Zn/Gd source, with a molar percentage of Gd ranging from 0% (pure ZnO) to 5%, 10%, or 15%, in a constant O₂/Ar gas mixture flowing at 500° C. The pure ZnO nanocrystals exhibited a strong and predominant UV emission peaking at 375 nm. Besides the UV emission of ZnO nanocrystals, two strong blue emissions, located at 432 and 397 nm, are observed for the sample doped with 5% Gd. The strong blue emissions are mainly induced by the impurity levels of Gd introduced into the band gap of the ZnO nanocrystals. The UV emission of ZnO decreases as the doping concentration of Gd increases, and the blue emission is replaced by a broad defect emission due to the greater number of defects and impurities, as well as Gd₂O₃ on the surface. The results show that the optical properties of ZnO can be tuned by the doping concentration of Gd.     

Nitrogen-doped ZnO/n-Si core–shell nanowire photodiode prepared by atomic layer deposition

Photodiodes made from core–shell nanowires (NWs) comprising n-type silicon (n-Si; core) and nitrogen-doped ZnO (ZnO:N; shell) were fabricated by atomic layer deposition of ZnO:N on vertically aligned Si NWs. The device properties were investigated as functions of nitrogen content of the ZnO:N shell. The electron-carrier concentration of ZnO:N was modulated by adjusting the concentration of the reactant, diluted ammonium hydroxide, from 0 to 30%. The rectification ratio and the reverse-current density of the ZnO:N/n-Si planar heterojunction were evaluated under dark condition for various NH₄OH concentrations. The ZnO:N/n-Si heterojunction prepared with NH₄OH 15% was found to have the lowest reverse-current density with a moderate resistivity. In order to realize an effective ZnO:N/n-Si photodiode, a ZnO:N layer prepared with 15% NH₄OH was deposited on well-aligned Si nanowires. The core–shell NW photodiode showed more sensitive photodetecting performance in UV light than the planar photodiode. Also, the significantly enhanced performances of the core–shell NW photodiode were evaluated by examining its spectral responsivity.     

Optical properties of Eu3＋, Dy3＋ co-doped ZnO nanocrystals

ZnO nanocrystals doped with trivalent europium ions （Eu3＋） and dysprosium ions （Dy3＋） were synthesized by the pre- cipitation method. The structural and optical properties of the samples are investigated by the X-ray diffraction （XRD） and photoluminescence （PL）. The results show that rare earth ions are incorporated into the lattice of ZnO, and the combination of blue, green and red emissions can be obtained. Specially, the emission can be obtained even under the nonresonant excitation of 320 nm, which is explained based on the energy transfer. The concentration quenching mechanism is also presented in this paper.     

ZnO纳米管的制备及光学特性研究

ZnO nanotubes have been fabricated through a carbon thermal reduction deposition process. Structure characterization results show that the ZnO nanotubes have a single crystalline wurtzite hexagonal structure pref- erentially oriented in the c-axis. The diameters of ZnO nanotubes are in the range of 90-280 nm and the wall thickness is about 50-100 nm. Room-temperature photoluminescence measurements of the ZnO nanotubes exhibit an intensive ultraviolet peak at 377 nm and a broad peak centered at about 517 nm. The UV emission is caused by the near band edge emission while the green emission may be attributed to both oxygen vacancy and the surface state. Raman and cathodoluminescence spectra are also discussed. Finally, a possible growth mechanism of the ZnO nanotubes is proposed.     

Synthesis and characterization of ZnS/ZnO/CdS nanocomposites

Water-soluble ZnS/ZnO/CdS (0.1–0.5 M) nanocomposites were successfully synthesized by the chemical precipitation method in air. X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis), photoluminescence (PL) and thermo gravimetric-differential thermal analysis (TG-DTA) were used to characterize the synthesized products. It is found that the ZnS/ZnO/CdS (0.1–0.5 M) core–shell nanocomposite is cubic and hexagonal mixed structure. TEM results showed the prepared nanocomposites are monodispersed and uniform in size. It is confined within 4.3–5.6 nm range. UV–vis absorption spectra were confined growth process of multi shells on ZnS. It showed a red shift with respect to the shells thickness. Fluorescence measurement showed the emission band which exists in the visible region. Stability and phase transition were identified by TG-DTA analysis. The results show an improved florescence property, indicating their potential applications in biological labeling.     

Effect of surfactants on morphology, structure and photoluminescence properties of Eu-doped ZnO microsphere

The influence of polyvinylpyrrolidone (PVP) and monoethanolamine (MEA) as surfactants on photoluminescence (PL) of Eu-doped ZnO (ZnO:Eu) has been studied. X-ray diffraction (XRD) results show that there are more Eu3+ ions to replace Zn2+ ions into ZnO lattice for ZnO:Eu in the presence of surfactant MEA. From the spectral analysis for ZnO:Eu with different surfactants by Gaussian deconvolution, it can be seen that the use of MEA as a surfactant affects the energy transfer from ZnO host to Eu3+ ions and leads to three new emission peaks, including UV emission (389 nm), violet emission (411 nm) and green emission (506 nm).     

ZnO:Al/n-ZnO/p-GaN异质结电致发光特性研究

利用ZnO和GaN材料制备了ZnO:Al/n-ZnO/p-GaN透明电极异质结发光二极管。通过SEM、TEM和荧光光谱对ZnO纳米棒进行了结构表征和发光特性表征。通过半导体特性分析系统和光谱测试技术对ZnO:Al/n-ZnO/p-GaN异质结进行了电致发光性能测试和机理分析。结果表明该器件能产生有效的蓝紫色电致发光,其发光分别来自于n型ZnO、p型GaN以及界面辐射;并且采用ZnO:Al作为透明电极可以提高该器件的出光效率。该异质结可应用于高效率短波发光器件。     

Wavelength‐Emission Tuning of ZnO Nanowire‐Based Light‐Emitting Diodes by Cu Doping: Experimental and Computational Insights

The band‐gap engineering of doped ZnO nanowires is of the utmost importance for tunable light‐emitting‐diode (LED) applications. A combined experimental and density‐functional theory (DFT) study of ZnO doping by copper (Zn²⁺ substitution by Cu²⁺) is presented. ZnO:Cu nanowires are epitaxially grown on magnesium‐doped p‐GaN by electrochemical deposition. The heterojunction is integrated into a LED structure. Efficient charge injection and radiative recombination in the Cu‐doped ZnO nanowires are demonstrated. In the devices, the nanowires act as the light emitters. At room temperature, Cu‐doped ZnO LEDs exhibit low‐threshold emission voltage and electroluminescence emission shifted from the ultraviolet to violet–blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the copper content in the ZnO nanoemitters. The shift is explained by DFT calculations with the appearance of copper d states in the ZnO band‐gap and subsequent gap reduction upon doping. The presented data demonstrate the possibility to tune the band‐gap of ZnO nanowire emitters by copper doping for nano‐LEDs.     

应力对ZnO/Si异质结构的光致发光的影响

研究了ZnO薄膜中应力对发光的影响.实验样品为ZnO体单晶、在Si基片上直接生长的ZnO薄膜以及通过SiC过渡层在Si基片上生长的ZnO薄膜.测量了这三种样品的X射线衍射图形、喇曼光谱和光致发光光谱.由X射线衍射图形可以看出,由于SiC过渡层缓解了ZnO与Si之间的晶格失配,使得通过SiC过渡层在Si上生长的ZnO薄膜的结晶质量好于直接在Si上生长的ZnO薄膜的质量.进一步通过喇曼谱测量发现,与ZnO体单晶相比,直接在Si上生长的ZnO薄膜的E2(high)峰红移1.9cm-1,根据喇曼谱峰位移与应力的关系可以推出薄膜中存在0.4GPa的张应力;而通过SiC过渡层在Si上生长的ZnO薄膜的E2(high)峰红移0.9cm-1,对应着0.2GPa的张应力.对照X射线衍射图形的结果可以看出,薄膜中张应力的大小与薄膜的结晶质量密切相关,表明张应力来源于外延层和基片间的晶格失配,晶格失配越大,外延层中产生的张应力越大.有无SiC过渡层的两种薄膜样品的PL光谱中都存在紫外和绿光两种谱带,随样品热处理时氧气分压增加,两种样品都出现绿光增强的相似的变化规律,但有SiC过渡层的样品的变化幅度较小.这一结果说明,绿色发光中心与薄膜的质量,也就是与薄膜中存在的张应力大小有关.在以往研究中得出的非故意掺杂ZnO薄膜的绿色发光中心来源于氧反位缺陷(Ozn),文中研究的结果正好可以解释氧反位缺陷形成的原因.由于薄膜中存在张应力,使得样品的能量升高,其结果必然会产生缺陷来释放张应力,以便降低系统能量.而氧离子半径大于锌离子半径,氧替位锌有利于释放张应力,也就是说,在存在张应力的情况下,Ozn的形成能降低.这一结果进一步证明Si上生长的ZnO薄膜中的绿色发光中心与氧反位缺陷有关.     

Hierarchical Nanowire Arrays Based on ZnO Core−Layered Double Hydroxide Shell for Largely Enhanced Photoelectrochemical Water Splitting

Well‐aligned hierarchical nanoarrays containing ZnO core and layered double hydroxide (LDH) nanoplatelets shell have been synthesized via a facile electrosynthesis method. The resulting ZnO@CoNi–LDH core?shell nanoarray exhibits promising behavior in photoelectrochemical water splitting, giving rise to a largely enhanced photocurrent density as well as stability; much superior to those of ZnO‐based photoelectrodes. This is attributed to the successful integration of photogenerated electron–hole separation originating from the ZnO core and the excellent electrocatalytic activity of LDH shell. This work provides a facile and cost‐effective strategy for the fabrication of multifunctional nanoarrays with a hierarchical structure, which can be potentially used in energy storage and conversion devices.     

Effect of Lattice Mismatch on Luminescence of ZnO/Si Hetero-Structure

研究了ZnO薄膜中应力对发光的影响.实验样品为ZnO体单晶、在Si基片上直接生长的ZnO薄膜以及通过SiC过渡层在Si基片上生长的ZnO薄膜.测量了这三种样品的X射线衍射图形、喇曼光谱和光致发光光谱.由X射线衍射图形可以看出,由于SiC过渡层缓解了ZnO与Si之间的晶格失配,使得通过SiC过渡层在Si上生长的ZnO薄膜的结晶质量好于直接在Si上生长的ZnO薄膜的质量.进一步通过喇曼谱测量发现,与ZnO体单晶相比,直接在Si上生长的ZnO薄膜的E2(high)峰红移1.9cm-1,根据喇曼谱峰位移与应力的关系可以推出薄膜中存在0.4GPa的张应力;而通过SiC过渡层在Si上生长的ZnO薄膜的E2(high)峰红移0.9cm-1,对应着0.2GPa的张应力.对照X射线衍射图形的结果可以看出,薄膜中张应力的大小与薄膜的结晶质量密切相关,表明张应力来源于外延层和基片间的晶格失配,晶格失配越大,外延层中产生的张应力越大.有无SiC过渡层的两种薄膜样品的PL光谱中都存在紫外和绿光两种谱带,随样品热处理时氧气分压增加,两种样品都出现绿光增强的相似的变化规律,但有SiC过渡层的样品的变化幅度较小.这一结果说明,绿色发光中心与薄膜的质量,也就是与薄膜中存在的张应力大小有关.在以往研究中得出的非故意掺杂ZnO薄膜的绿色发光中心来源于氧反位缺陷(Ozn),文中研究的结果正好可以解释氧反位缺陷形成的原因.由于薄膜中存在张应力,使得样品的能量升高,其结果必然会产生缺陷来释放张应力,以便降低系统能量.而氧离子半径大于锌离子半径,氧替位锌有利于释放张应力,也就是说,在存在张应力的情况下,Ozn的形成能降低.这一结果进一步证明Si上生长的ZnO薄膜中的绿色发光中心与氧反位缺陷有关.     

Investigation of luminescence properties of ZnO nanowires at room temperature

The controllable growth processes of ZnO nanowires by evaporation of metal zinc with high purity and its luminescence properties have been investigated in detail. Firstly, the power of ZnO nanowires with high yield and homogeneous dimension was synthesized using the special quartz boat at 600 °C. Then, the oriented ZnO nanowires with about 20 nm diameter were synthesized by using a 90 nm-thick layer of ZnO nanocrystals on the Si substrate as the seed layer. Both fabrication processes are repeatable and no catalysts are necessary. Finally, photoluminescence (PL) spectroscopy for ZnO nanowires using an He-Cd laser line of 325 nm as the excitation source were measured at room temperature and both samples showed a sharp strong ultraviolet (UV) near-band edge emission. However, different UV peak positions (385 nm for ZnO nanowire powder, 377 nm for ZnO nanowire array) can be observed. The size confinement effect for excitons and carriers is proposed to explain the blue shift of the near-band edge emission with decreasing size and the native defects are responsible for the green emission.     

Synthesis and optical properties of two novel ZnO flowerlike and spindlelike nanostructures

A new aqueous chemical growth method for generation of ZnO flowerlike and spindlelike nanostructures, transformed from layered basic zinc acetate (LBZA) nanobelts, is developed. The novel as-synthesized ZnO flowerlike and spindlelike nanostructures are mainly due to the pH. They are characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction peaks indicate that these ZnO nanostructures prefer to grow along the C-axis. Photoluminescence (PL) measurements show that the ZnO flowerlike nanostructures have strong ultraviolet (UV) emission properties at 380 nm, while no defect-related visible emission can be detected. The good performance for photoluminescence emission makes the ZnO flowerlike nanostructures to be promising candidates for photonic and electronic device applications.     

纳米ZnO薄膜的热蒸发法制备及其光电特性研究

以醋酸锌为原料、O/Ar的混合气体为携载气体,在500℃的温度下应用热蒸发法在p型Si基片上生长纳米ZnO薄膜,并研究了其形貌、结构和光电特性.X-射线(XRD)衍射结果显示所制备ZnO纳米晶体呈六角纤锌矿结构;扫描电子显微镜(SEM)观察发现生长的Zn0薄膜平整均匀,纳米晶体颗粒平均尺寸为25nm.应用紫外-可见光吸收谱分析了其吸收特性,发现该ZnO薄膜在紫外波段具有很强的吸收,其吸收边位于320nm处.由于量子限制效应,与体材料相比,该吸收边存在明显的蓝移.应用光致发光谱(PL)研究了其发光特性,发现该ZnO薄膜在近紫外以及蓝-绿光波段具有强烈的受激发射.最后,还研究了ZnO薄膜的电容-电压(C-V)特性.