Red luminescence from hydrothermally synthesized Eu-doped ZnO nanoparticles under visible excitation

Eu-doped ZnO nanoparticles were synthesized by hydrothermal method. The Eu-dopant concentration has been varied by varying the amount of Eu-dopant concentration. These nanoparticles were structurally characterized by X-ray diffraction, transmission electron microscopy and selected area electron diffraction and it confirms the formation of nanoparticles having standard wurtzite structure. Photoluminescence studies show that these nanoparticles exhibit a sharp red luminescence due to the intra-4f transitions of Eu³⁺ ions at an excitation of 397 nm and 466 nm. Luminescence quenching is observed in the nanoparticles as the Eu-dopant concentration increases. Incorporation of Eu in the nanoparticles was confirmed by the energy dispersive X-ray studies.     

Visible luminescence mechanism of ZnO nanoparticles synthesized by sol-gel method

We presented our investigations on the absorption and emission properties of the nanocrystalline ZnO particles of different particle sizes (2 nm-5 nm) by sol-gel method. In the room temperature PL spectra, three emission bands, ultraviolet (UV), blue and green were observed. With increasing the particle sizes, both the UV and the visible emission bands shifted to lower energies progressively. From the size-dependency, there was a linear relationship between the energetic maxima of the UV and the green emission bands with a slope of about 0.26, which indicated that the green luminescence of ZnO was produced by the transitions of electrons from deep level to the valence band (or shallow acceptor level). A linear dependence was also found between the energetic maxima of the UV and the blue emissions with a slope of 0.15, the origin this blue emission band is not clear at present. While in van Dijken et al.'s paper, however, they identified only two emission bands in the emission spectra, an UV and a broad visible emission band, and the linear fit between the energetic maxima of these two bands in particles of different sizes has a slope of 0.6, so they proposed that the visible emission in ZnO was originated from the recombination of a shallowly trapped electron with a deeply trapped hole. We attributed this divergence to the fact that the broad visible band is actually composed of two separate emission bands originated from two different recombination processes, and should not had been treated as one emission band.     

多壁碳纳米管负载镁掺杂氧化锌纳米颗粒的研究

利用醋酸锌和醋酸镁为原料,无水乙醇为溶剂,草酸为沉淀剂,通过共沉淀法和后续热处理实现多壁碳纳米管表面负载镁掺杂氧化锌纳米颗粒,并使用X射线衍射仪、扫描电子显微镜、透射电子显微镜和紫外吸收光度计研究复合材料的形貌和光学性能。电子显微镜结果表明,在450℃热处理下,多壁碳纳米管表面能够均匀地负载镁掺杂氧化锌纳米颗粒,其颗粒粒径大约为10～20nm。紫外吸收光谱结果说明,镁掺杂显著地提高多壁碳纳米管/氧化锌复合材料的紫外吸收性能,而且其紫外吸收峰向短波方向蓝移达22nm。     

Highly efficient multiphoton-absorption-induced luminescence from gold nanoparticles

We demonstrate that highly efficient photoluminescence is generated from gold nanoparticles as small as a few nanometers in diameter upon irradiation with sub-100-fs pulses of 790-nm light. Strong emission is observed at excitation intensities comparable to or less than those typically used for multiphoton imaging of fluorescently labeled biological samples. The particles have polarized emission, can radiate more efficiently than single molecules, do not exhibit significant blinking, and are photostable under hours of continuous excitation. These observations suggest that metal nanoparticles are a viable alternative to fluorophores or semiconductor nanoparticles for biological labeling and imaging.     

Enhancement of green luminescence of ZnO powders by annealing with carbon black

This paper reports the characterization of nanocrystalline ZnO powders synthesized by a precipitation method and annealed with carbon black. The X-ray diffraction (XRD) and Fourier Transformed Infrared (FT-IR) results revealed that the synthesized ZnO powder has the wurtzite structure with absorbed CO₃^? species on the surface of the ZnO particles. Singly ionized oxygen vacancy (V_O⁺) and CO₃^? species were also perceived from electron paramagnetic resonance (EPR) analysis. The intensity of the EPR signals of CO₃^? species increased as the amount of carbon increased whereas that of V_O⁺ did not vary significantly. A green emission at 528 nm for the powders annealed with carbon was observed and a good correlation between the intensity of green emission and the intensity of EPR signals of CO₃^? was obtained Experimental results suggest that the formation of the free carriers has significant effect on the intensity of the green emission. The mechanism responsible for the green emission enhancement based on the relevance of the observations is discussed.     

Peculiarities of formation and luminescence of ZnS nanoparticles modified with amino acids

Surface modification of ZnS nanoparticles with various amino acids leads to dramatic changes in luminescence: 30-40-fold increase in the case of glycine and methionine and almost total disappearance of luminescence in the case of cysteine. The study of formation of “nacked” and surface-modified ZnS revealed two main stages: quite rapid process of generation of ZnS nanoparticles and relatively slow process of the formation of the luminescent centers. The last are the surface defected zinc ions, capped with amino acid in the case of modified species.     

Highly efficient luminescence from hybrid structures of ZnO/multi-walled carbon nanotubes for high performance display applications

We report an interesting observation on strong enhancement in green luminescence from hybrid ZnO/multi-walled carbon nanotubes (MWCNTs). The hybrid structures were synthesized via a high temperature sintering method. The strong green emission at 510 nm has been attributed to surface defects of ZnO, originating from interactions between ZnO and the MWCNT surface, which has been confirmed by high resolution transmission electron microscopy and x-ray photoelectron spectroscopy. Furthermore, the two-dimensional (2D) layer of this hybrid material shows a high degree of homogeneity and 82% transparency. Time resolved emission spectroscopy measurement shows a photoluminescence decay time in microseconds, which is suitable for making optoelectronic devices.     

Enhanced luminescence from lanthanide complex by silver nanoparticles

Photoluminescence of europium complex, Eu(III)DPA, where DPA is dipicolinic acid, in the presence of 5 nm-diameter Ag nanoparticles, was studied. Pronounced enhancement of Eu(III) luminescence was observed in the complex solution containing Ag nanoparticle with a concentration below 3.0 × 10¹³/ml. The dependencies of emission intensity of ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ transition on the concentration of Ag nanoparticles are quite different, the enhancement of electric dipole transition is stronger than that of magnetic dipole transition. There is no significant change in fluorescence lifetime in enhanced luminescence. The enhancement was attributed to a strong coupling between the radiation transition and surface plasmon resonance.     

Growth of ZnO nanowires on modified well-aligned carbon nanotube arrays

Single-crystal ZnO nanowires were successfully grown on modified well-aligned carbon nanotube (CNT) arrays by a hydrothermal process. The pre-deposited ZnO grains on the CNTs served as the nucleation sites for the growth of ZnO nanowires. The attached growth of ZnO nanowires on the well-aligned CNT arrays formed a 3D configuration. The 3D hybrid nanostructured material could find application in sensors and other electronic or optoelectronic devices.     

Dielectric investigations of pristine and modified ZnO nanoparticles for energy storage devices

Pristine ZnO, Al-doped ZnO, and TiO₂ coated ZnO nanoparticles (NPs) were synthesized by the wet chemical precipitation technique. All the synthesized NPs were characterized using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy. XRD analysis of pristine ZnO and Al-doped ZnO NPs revealed the hexagonal wurtzite structure with P6₃mc space group with no secondary phases and impurities. FESEM micrographs also depicted hexagonal grains with well-defined grain boundaries. TEM images showed hexagonal polyhedral shape for pure ZnO NPs and spherical shape dominating polyhedral particle for Al-doped ZnO NPs, and pseudospherical particles for TiO₂ coated ZnO NPs. Energy-dispersive X-ray spectroscopy of Al-doped ZnO indicates the eminent exchange of dopant in the lattice site of Zn. Dielectric Studies reveal the highest value of the dielectric constant and lowest value of dielectric loss for Al-doped ZnO as compared to pure and TiO₂-coated ZnO NPs. Suggesting Al-doped ZnO to be used as a dielectric material that can serve as a basic building block of the energy storage devices such as dielectric capacitor. TiO₂-coated ZnO NPs demonstrated higher AC conductivity in comparison to pure ZnO and Al-doped ZnO NPs suggesting their use as a conductive nanofiller materials in a polymer-based nanocomposite to achieve higher energy density.

     

Enhanced luminescence of Ag-decorated ZnO nanorods

Ag-decorated ZnO nanorods were synthesized by thermal evaporation of a mixture of ZnO and graphite powders at 900 °C followed by wet Ag coating and thermal annealing. The ZnO nanorods had a rod-like morphology with a relatively uniform width and length. The widths and lengths of the nanorods ranged from 50 to 300 nm and up to a few hundred micrometers, respectively. The diameters of the Ag particles on the nanorods ranged from 10 to 100 nm. The dependence of the photoluminescence properties of Ag-decorated ZnO nanorods on the postannealing atmosphere was examined. Annealing resulted in an increase and decrease in the near band edge (NBE) and deep level (DL) emission intensities of Ag-coated ZnO nanorods, respectively, whereas both the NBE and DL emission intensities of uncoated ZnO nanorods were increased by annealing. The intensity ratio of NBE emission to DL emission of the Ag-coated ZnO nanorods was increased ~15-fold by hydrogen annealing. The underlying mechanism for NBE emission enhancement and DL emission suppression of Ag-coated ZnO nanorods by postannealing is discussed based on the surface plasmon resonance effect of Ag.     

Experimental and theoretical analyses of ZnO nanoparticles deposited onto single-wall carbon nanotubes

Experimental and theoretical studies were performed on Single Wall Carbon Nanotubes (SWCN) decorated with ZnO nanoparticles located on the surface of the SWCN. Measurements of High Resolution Transmission Electron Microscopy (HRTEM) and Photoluminescence were performed, and theoretical calculations were carried out under the Extended Hückel Tight Binding Approximation. HRTEM results provide information about the existence of SWCN with ZnO nanoparticles on top. A considerably enhancement in the Photoluminescence (PL) behavior of the hybrid system was obtained as compared to pristine SWCN. Calculated energy bands of the pristine SWCN provide an energy gap of 0.06 eV. When the ZnO cluster is located onto the SWCN the new system behaves as a metal. Analysis of total and Partial Density of States (PDOS) provides information about each atom orbital contribution to the total DOS. It is shown that carbon contributes with p-orbitals while Zn contributes with p- and a very small contribution of d-orbitals. The overlap of all these contributions produces hybridized orbitals, which may likely be responsible for the enhancement of Photoluminescence on the new hybrid system.     

Spatially resolved luminescence properties of ZnO tetrapods

ZnO tetrapods were prepared by Zn-vapour deposition at 740 °C in Argon and subsequent oxidation in air for 1–30 min. The photoluminescence (PL) and cathodoluminescence (CL) spectra were measured from ZnO particles collected at various distances from the Zn source representing decreasing dimensions. The ZnO tetrapods showed a green emission centred at 516 nm (2.40 eV) band and the exciton emission at 387 nm (3.20 eV). The measured data suggested that the green emission is strongly increased for particle sizes below 500 nm, whereas the exciton emission is dominant for particle size larger than 500 nm. Spatially resolved CL-measurement on individual tetrapod legs showed, that the green emission increases with decreasing ZnO leg diameter. To our knowledge, the local CL spectroscopic measurements were correlated with the dimensions of the individual ZnO tetrapods for the first time.     

Strong green luminescence of Mg-doped ZnO nanowires

The ZnO nanowires doped with Mg (Mg-ZnONWs) were produced by thermally oxidizing Zn and Mg powders. TEM and XRD patterns indicated that Mg-ZnONWs were crystalline with a wurzite structure. The Mg doping was confirmed with XPS measurements. The green emission band at 500 nm in the photoluminescence spectrum of Mg-ZnONWs and peaks at 366 nm in low intensity were observable. Raman spectrum indicated that oxygen deficiency was not the dominant factor for the green emission. The green emission was further directly observed with a digital camera.     

ZnO:Zn的光致发光和电致发光性能

在N2 H2还原气氛中以ZnO粉末为原料制备了ZnO:Zn发光膜和粉末.利用X射线衍射、电子扫描显微镜、红外光谱仪、XPS、荧光分光光度计等测试手段表征了样品的结构、形貌、缺陷和发光性能.ZnO:Zn发光膜具有六角纤锌矿晶体结构和良好的c轴取向,结晶性较好,晶粒颗粒均匀.ZnO:Zn发光膜和粉末具有绿色的单谱光致发光和电致发光.发光薄膜的O1s结合能表明,此绿色发光与薄膜内的点缺陷状态密切相关.     

Excitonic luminescence in ZnO nanopowders and ceramics

Fast photoluminescence spectra in the spectral region of 3.1–3.45 eV in ZnO and ZnO:Al ceramics were studied at 14 and 300 K. Ceramics with grains smaller than 100 nm were sintered from nanopowders by high pressure (8 GPa) and low temperature (350 °C). Ceramics with grain sizes 1–5 μm were sintered at 1400 °C. It is shown that excitonic luminescence spectra depend on the ceramics grain size, post preparing annealing and doping. The excitonic luminescence decay time was faster than 2 ns and the afterglow at 30 ns was 0.05%.     

Blue luminescence from porous layers produced by metal-assisted chemical etching on low-doped silicon

Photoluminescent porous layers were formed on highly resistive p-type silicon by a metal-assisted chemical etching method using K₂Cr₂O₇ as an oxidizing agent. A thin layer of Ag is deposited on the (1 0 0) Si surface prior to immersion in a solution of HF and K₂Cr₂O₇. The morphology of the porous silicon (PS) layer formed by this method as a function of etching time was investigated by scanning electron microscopy (SEM). It shows that the surface is formed by macropores filled with microporous silicon. The porous layers were characterized by backscattering spectrometry (BS) as a function of etching time in random and channelling mode. Channelling spectra show that the porous layer remains crystalline after etching. On the other hand, random and channelling spectra show that the deposited silver diffuses into the pore. Luminescence from metal-assisted chemically etched layers was measured. It was found that the PL intensity increases with increasing etching time. This behaviour is attributed to increase of the density of the silicon nanostructure. Finally, the PL spectra show two peaks of emission at 450 and 600 nm.     

Synthesis and luminescence property of rare earth complex nanoparticles dispersed within pores of modified mesoporous silica

A rare earth complex, Eu(AA)₃Phen was successfully introduced into the pores of mesoporous silica, which was verified by X-ray photoelectron spectroscopy and nitrogen sorption isotherms. The rare earth complex dispersed in mesoporous silica displayed characteristic fluorescence emission of the pure rare earth complex, and the fluorescence emission was enhanced, especially for that with diamine treated mesoporous silica.     

Immobilization of Prussian Blue nanoparticles onto thiol SAM modified Au electrodes for electroanalytical or biosensor applications

Poly(vinylpyrrolidone) (PVP)-protected Prussian Blue (PB) nanoparticles were prepared by simply mixing FeCI3 and K4Fe(CN)6 with absence or presence of HCI or/and KCI in water solution. The obtained PB nanoparticles were immobilized onto thiol self-assembled monolayer (SAM) modified Au electrodes. L-cysteine (Cys) and 1,8-octanedithiol (ODT) were compared as a bridge between the gold surface and the PB nanoparticles. The results show that PB prepared from the initial solution with KCI gives preferred electrochemical response and that Cys/Au shows improved immobilization effect of PB than ODT/Au. The obtained PB/Cys/Au electrodes exhibit electrocatalytic activity toward H2O2 reduction and DL-homocysteine (HCys) oxidation. Glucose oxidase (GOX) was immobilized onto PB modified electrode to explore the potentials for the design of oxidase-based biosensors. It is possible to anchor PB nanoparticles and develop their application on electroanalysis and biosensing.