ZnO nanoparticles embedded in sapphire fabricated by ion implantation and annealing

ZnO nanoparticles were fabricated in sapphire (α-Al(2)O(3) single crystal) by Zn ion implantation (48?keV) at an ion fluence of 1 × 10(17)?cm(-2) and subsequent thermal annealing in a flowing oxygen atmosphere. Transmission electron microscopy (TEM) analysis revealed that metallic Zn nanoparticles of 3-10?nm in dimensions formed in the as-implanted sample and that ZnO nanoparticles of 10-12?nm in dimensions formed after annealing at 600?°C. A broad absorption band, peaked at 280?nm, appeared in the as-implanted crystal, due to surface plasma resonance (SPR) absorption of metallic Zn nanoparticles. After annealing at 600?°C, ZnO nanoparticles resulted in an exciton absorption peak at 360?nm. The photoluminescence (PL) of the as-implanted sample was very weak when using a He-Cd 325?nm line as the excitation source. However, two emission peaks appeared in the PL spectrum of ZnO nanopraticles, i.e., one ultraviolet (UV) peak at 370?nm and the other a green peak at 500?nm. The emission at 500?nm is stronger and has potential applications in green/blue light-emitting devices.     

Template-free solvothermal synthesis of ZnO nanoparticles with controllable size and their size-dependent optical properties

ZnO nanoparticles (NPs) have been synthesized via a facile and template-free solvothermal method. The size of ZnO NPs could be tailored by adjusting the ratio of ethanol to ethylene glycol (EG). Their structure and morphology have been investigated. The as-prepared samples are monodispersed ZnO NPs with controllable sizes of about 24.2, 18.9 and 14.7 nm. The cathodoluminescence (CL) spectra of the samples show that the relative intensity ratio of the visible emission peak at 500-650 nm to the band-edge UV emission peak at 380 nm increases as the particle size decreases. Sample with smaller crystallites would have larger surface area and more oxygen vacancy defects, thus it exhibits higher visible emission peak. The UV-vis absorption spectrum indicates the band gap variation of the ZnO NPs with their size. Moreover, the size-dependent blue shifts of both the CL emission and the UV-vis absorption spectra reveal the effect of quantum confinement.     

Fabrication of ZnO tetrapods on silicon substrate by thermal evaporation

Large-scale ZnO tetrapods have been fabricated on silicon substrate by a simple thermal evaporation method at 700 °C without vapor transportation and characterized by FESEM, XRD, Micro-Raman, and PL, respectively. FESEM images indicate that the length of tetrapod arm is about 3–4 μm, and the diameter of the tip is about 50 nm. XRD and Raman spectrum reveal that ZnO tetrapods are highly pure hexagonal wurtzite structure. The PL spectrum indicates that the ZnO tetrapods have strong green emission at 510 nm.     

Zn-catalysed growth and optical properties of modulated ZnO hierarchical nanostructures

Modulated ZnO hierarchical nanostructures have been successfully synthesised by the one-step thermal evaporation method. The ZnO hierarchical nanostructures consist of large quantities of high-dense nanowires strewn with some small balls, and these balls are connected with wires by short rods. The composition detection results show that the ball is metallic Zn, which further confirms that Zn can serve as the catalyst for vapour–liquid–solid growth of the ZnO hierarchical nanostructures. The photoluminescence spectrum of the modulated ZnO hierarchical nanostructures includes a weak ultraviolet peak centred at 380?nm and a strong green emission centred at 500?nm, which can be attributed to the exciton emission at the near-band edge and a mass of singly ionised oxygen vacancies in products, respectively.     

Cl~-,S~(2-)共掺杂氧化锌荧光粉的制备及发光性能

在空气气氛中,以NH_4Cl为助剂,通过热氧化硫化锌,制备出Cl~-,S~(2-)共掺杂氧化锌荧光粉,激发和发射光谱随氧化温度的变化而变化.在350nm激发下,氧化锌荧光粉的发射光谱只有510nm绿色峰,并有黄色区拖尾现象.绿色峰强度随煅烧温度的变化而变化.绿色峰归因与一价氧空位中的电子和价带中光生空穴的复合.氧化锌荧光粉的光致发光谱的变化是Cl~-,S~(2-)共掺杂的结果.     

ZnO单晶体的荧光温度特性

通过变温荧光光谱研究了ZnO激子发光的温度依赖特性。在6K的低温下,其光致发光主要来自束缚激子能量位于3.360eV,半宽为3meV的施主束缚激子发光。而随着测量温度的上升,自由激子及其声子辅助跃迁发光逐渐成为ZnO主要发光机制。文中详细讨论了ZnO荧光随温度的演变过程。特别是自由激子的声子伴线与自由激子发光峰之间的能量间距,随温度的上升逐渐偏离了其特征声子模能量,呈现不断缩小趋势。     

Optical and structural characteristics of ZnO thin films grown by rf magnetron sputtering

Nanostructured ZnO thin films on Pyrex glass substrates were deposited by rf magnetron sputtering at different substrate temperatures. Structural features and surface morphology were studied by X-ray diffraction and atomic force microscopy analyses. Films were found to be transparent in the visible range above 400 nm, having transparency above 90%. Sharp ultraviolet absorption edges around 370 nm were used to extract the optical band gap for samples of different particle sizes. Optical band gap energy for the films varied from 3.24 to 3.32 eV and the electronic transition was of the direct in nature. A correlation of the band gap of nanocrystalline ZnO films with particle size and strain was discussed. Photoluminescence emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.     

Synthesis of novel zinc oxide microphone-like microstructures

Novel microphone-like ZnO microstructures were grown at a very high density via a simple thermal evaporation process using commercially available ZnO powder in ambient air at ∼ 1050 ± 20 °C in 1 h. The unique as-grown microstructures were characterized in detail in terms of their structural and optical properties. The structural properties of the synthesized products confirmed that they were wurtzite hexagonal phase for the as-grown products. Raman-scattering spectra exhibited a strong and dominated Raman-active E₂ (high) mode at 441 cm^− 1, confirming the wurtzite hexagonal phase for the as-grown microphone-like ZnO morphologies. The cathodoluminescence (CL) spectrum shows a suppressed near band edge emission at ∼ 380 nm and strong green emission at ∼ 500 nm.     

Preparation,characterization and optical properties of nanostructured ZnO thin films

Nanostructured ZnO thin film on a glass slide has been prepared by the spin-coating method together with calcining at 500 °C for 2 h in flowing oxygen atmosphere. The grain size of the ZnO nanoparticles is estimated to be ca. 12 nm as determined by the absorption spectrum and powder X-ray diffraction analysis. The photoluminescent peaks that centered at ca. 379 and 388 nm are assigned to the spontaneous emission and exciton–exciton emission, respectively. The thin film also shows frequency-tripled properties for the output when the laser beam of 1.06 μm is input in convergent beam.     

Enhanced surface-excitonic emission in ZnO/Al(2)O(3) core-shell nanowires

We report the influence of an Al(2)O(3) shell on the photoluminescence emission of ZnO nanowires. At room temperature, the spectrum of the core-shell nanowires shows a strong reduction of the relative intensity of the green defect emission with respect to the near-band-edge emission. At 5?K an increase of the relative intensity of the surface exciton band with respect to the donor-bound exciton emission is observed. Annealing the core-shell nanowires at 500?°C does not increase the green defect luminescence at 5?K. We propose a model explaining the spectral changes.     

Excitons emissions and Raman scattering of ZnO nanoparticles embedded in BaF2 matrices by reactive magnetron sputtering

ZnO nanoparticles embedded in BaF2 matrix were fabricated by rf magnetic sputtering technology. The optical properties of high quality ZnO nanoparticles, thermally post treated in a N2 atmosphere, were investigated by temperature-dependence photoluminescence measurement. Free exciton and localized exciton were observed at the low temperature. Free exciton peak was at 3.374 eV and localized exciton peak was at 3.420 eV, dominating the PL spectrum at 77 K. Free exciton transition was observed at 3.310 eV at room temperature, whereas the localized exciton transition was at 3.378 eV. The multiple-phonon Raman scattering spectrum showed that ZnO nanoparticles embedded in BaF2 matrix had a large deformation energy originated from lattice mismatch between ZnO and BaF2 matrix. Analysis of the fitting results from the temperature dependence of FWHM of ZnO exciton illustrated that the large value of gamma(ph) was good qualitative agreement with the large deformation potential.     

高压PLD法生长p型钠掺杂氧化锌纳米线阵列

采用高压脉冲激光沉积法(HP-PLD)研究了压强、金催化层厚度对钠掺杂氧化锌纳米线(ZnO:Na)生长的影响, 并制备了ZnO:Al薄膜/ZnO:Na纳米线阵列同质pn结器件。实验发现, 当金膜厚度为4.2 nm, 生长压强为3.33×10⁴ Pa, 生长温度为875℃时, 可在单晶Si衬底上生长c轴取向性良好的ZnO纳米线阵列。X射线衍射和X射线光电子能谱综合分析证实了Na元素成功掺入ZnO纳米线晶格中。在低温(15 K)光致发光谱中, 观测到了一系列由Na掺杂ZnO产生引起的受主光谱指纹特征, 如中性受主束缚激子峰(3.356 eV, A0X)、导带电子到受主峰(3.312 eV, (e, A0))和施主受主对发光峰(3.233 eV, DAP)等。通过在ZnO:Al薄膜上生长ZnO:Na纳米线阵列形成同质结, 测得I-V曲线具有明显的整流特性, 证实了ZnO:Na纳米线具有良好的p型导电性能。     

Synthesis and characterization of ZnO tetrapods for optical and antibacterial applications

ZnO tetrapods have been grown by sublimation process employing thermal evaporation at 950 °C on quartz substrate. The grown ZnO tetrapods exhibited noteworthy microstructure, phase formation, emission bands and antibacterial performance. A detailed micro- and nano- analysis supported with analytical measurements elucidated the faceted tetrapod growth with hexagonal wurzite crystal structure of ZnO. Each arm of the tetrapod revealed a facetted hexagonal cross-section with uniform length and diameter. The photolumiscence spectra showed engrossing optical properties with pre-dominant green emission completely overwhelming the near band edge (NBE) UV peak. These fascinating tetrapod objects responded well for antibacterial activity against Escherichia coli and Staphylococcus aureus.     

In situ formation of Mn-doped ZnO aligned structures by rapid heating method

ZnO tetrapods and Mn doped multipods have been prepared by a rapid thermal oxidation at 1220 °C during 6 min. Moreover, Mn doped ZnO nearly aligned nanostructures forming carpets over sintered pellets have been produced by the same method without the use of catalyst or gas flow. These rods show two different diameters, one of 500 nm and the other one of 300 nm, with lengths of 5 µm. XRD and Raman spectra demonstrate a good crystalline quality of the doped nanostructures. The room temperature photoluminescence shows a quenching of the intrinsic UV emission band on the ZnO tetrapods, due to an increase of material defects.     

Enhancement of green emission from Sn-doped ZnO nanowires

Oxygen vacancies play a crucial role in the emission characteristics of oxide nanomaterials. In this study, we found that the green emission intensity of ZnO nanowires can be enhanced through a Sn-doping concentration which increases the number of oxygen vacancies. Undoped ZnO nanowires showed blue emission at 380 nm, but as the concentration of Sn was increased, the green emission peak at around 500 nm, which is attributed to oxygen vacancies, showed drastic enhancement. On the basis of XPS compositional analysis, it was confirmed that the green luminescence intensity was closely related to the number of oxygen vacancies in Sn-doped ZnO nanowires. These results pave the way to a greater understanding of tunable light emission from nanowires, which could be a key technology for next-generation display devices, including flexible and transparent displays.     

Stability and nonlinear optical properties of ZnO nanoparticles

Photoluminescence (PL) of ZnO nanoparticles of different surface states and sizes grown by several methods has been measured. The origin of luminescence and dependence of the luminescence spectrum shape and intensity on 325 nm excitation laser power are studied. Strong ultraviolet emission at 3.26 eV, weak violet emission around 3.12 eV and weak green emission at 2.40 eV have been observed in 16 nm nanoparticles capped by octylamine grown by non-hydrolytic method. The nanoparticles are stable under high power laser radiation and their PL intensity increases nonlinearly with an increasing laser power. As the nanoparticle size decreases to 12 nm, high power laser produces nonradiative centers which may quench the luminescence in a degree. Nanoparticles of 8 nm capped by PVP and uncapped nanoparticles of 14 nm are unstable and their luminescence depends on the excitation laser power. High power laser can quench O vacancy emission and enhance ultraviolet emission in PVP capped nanoparticles while vacancy emission can not be quenched in uncapped nanoparticles.     

A template-free alcoholthermal route to Ti(Sn)-doped ZnO nanorods

Ti(Sn)-doped single-crystalline ZnO nanorods with an average diameter of 20 nm and length up to nearly 1 μm were synthesized by a facile ultrasonic irradiation-assisted alcoholthermal method without involving any templates. Photoluminescence spectra of the Ti-doped ZnO nanorods were measured at room temperature and three emitting bands, being a violet emission at 400-415 nm, a blue band at 450-470 nm and a green band at around 550 nm, were detected. The emission intensities of the Ti-doped ZnO nanorods enhance gradually with increasing the doping concentrations. As to the Sn-doped ZnO nanorods, the green emission shifts to 540 nm and the emission intensities increase first but decrease later with increasing the doping concentrations.     

Vertical growth and resonator properties of hexagonally shaped zinc oxide nanonails

We synthesized vertically aligned nail-shaped ZnO nanocrystal arrays on silicon substrates via a combination of a carbothermal reduction method and textured ZnO seeding layers that were precoated on silicon substrates by thermally decomposing zinc acetate, and studied their optical properties using cathodoluminescence (CL) and photoluminescence techniques. The ZnO nanonails show a sharp band-gap edge UV emission and a defect-related broad green emission. Monochromatic CL images of an individual ZnO nanonail show variations in spatial distributions of respective CL bands that had different origins. We attribute the spatial variation of CL images to an uneven distribution of luminescent defects and/or a structure-related light out-coupling from hexagonal ZnO nanostructures. The most distinct CL feature from the hexagonal head of an individual ZnO nanonail was the occurrence of a series of distinct resonant peaks within the visible wavelength range. It appeared that the head of a nanonail played the role of a hexagonal cavity so that polarization-dependent whispering gallery modes were stimulated by electron beam excitation.     

Annealing effects on the structural and optical properties of growth ZnO thin films fabricated by pulsed laser deposition (PLD)

Annealed ZnO thin film at 300, 350, 400, 450 and 500 °C in air were deposited on glass substrate by using pulsed laser deposition. The effects of annealing temperature on the structural and optical properties of annealed ZnO thin films by grazing incident X-ray diffraction (GIXRD), transmittance spectra, and photoluminescence (PL) were investigated. The GIXRD reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye–Scherrer equation and the average grain size were found to be in the range 5.22–10.61 ± 0.01 nm. The transmittance spectra demonstrate highly transparent nature of the films in visible region (>70 %). The calculation of optical band gap energy is found to be in the range 2.95–3.32 ± 0.01 eV. The PL spectra shows that the amorphous film gives a UV emission only and the annealed films produce UV, violet, blue and green emissions this indicates that the point defects increased as the amorphous film was annealed.     

Optical emission and absorption spectra of Zn–ZnO core-shell nanostructures

The core-shell Zn–ZnO nanostructures were fabricated from Zn-powder embedded in graphite (i.e. carbon matrix) in a thin-films form by an inexpensive vacuum arc technique followed by laser ablation. The grazing incidence X-ray diffraction pattern shows that intensity of Zn-peak decreases, and subtle ZnO-peak increasing with the increase in laser power. The high resolution transmission electron microscopic study clearly exhibits the formation of a core-shell nanostructure as fabricated by laser ablation. The emission characteristics of laser ablated (with different powers) samples show a strong exciton peak at 388 nm, and a few more weak peaks (due to weak defect states in the visible range). The optical absorption spectra were obtained from the excitonic peaks (from 344 nm to 317 nm) on decreasing laser power. These peaks occur due to the coupling of exciton absorption (from ZnO shell layer) and core metal interband absorption. The Zn–ZnO core-shell nanostructure is useful for nanophotonic applications.