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Query: KEGG:D01170 (ZnO)
 13,684 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Electron-energy-loss near edge structures (ELNES) at the Zn-L(2,3) edge and the O-K edge have been measured for 10 mol% ZnO-doped MgO, and were compared with spectra from reference materials. In order to interpret the spectra, first principles molecular orbital calculations were made using model clusters composed of 125 and 153 atoms. Photoabsorption cross sections (PACS) were computed at the Slater's transition state in which a half-filled core hole was included in the self-consistent calculations. The difference in the coordination numbers of Zn was found well distinguishable by the Zn-L(2,3)-edge ELNES. The experimental spectra in the first 25 eV were well reproduced by the theoretical PACS. In this energy region, the Zn-L(2,3)-edge ELNES from four-fold coordinated Zn showed four sets of peaks, whereas the six-fold coordinated Zn exhibits three sets of peaks. The origin of these peaks can be explained by the point symmetry within the first coordination unit. A small shift toward the lower energy side was observed in the O-K edge ELNES of the ZnO-doped MgO as compared with pure MgO. This can be ascribed to the lower energy of the Zn-4s orbital as compared with the Mg-3s orbital, which is the common mechanism to the difference in the band gap between MgO and ZnO.
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PMID:Electron-energy-loss near edge structures of six-fold-coordinated Zn in MgO. 1128 Nov 56

A new structure with II-VI nano-crystal ZnO film as the electron transport layer and MEH-PPV as the hole transport layer and emitting layer was fabricated. The new structure's brightness and efficiency were improved markedly compared with that of the single MEH-PPV layer structure. And a new peak at 620 nm was found in the ITO/MEH-PPV/ZnO/Al structure's electroluminescence spectrum, which should resulted from ZnO layer. In addition, the turning-on voltage of the two-layer structure decreased from 9 V of the single layer structure to 4 V. From the I-V curve, the authors concluded that the emitting area was around the interface of MEH-PPV/ZnO and the combination area could shift with changing the voltage.
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PMID:[Electroluminescence property of MEH-PPV/ZnO nano-crystal structure]. 1576 13

Four different types of solar cells prepared in different laboratories have been characterized by impedance spectroscopy (IS): thin-film CdS/CdTe devices, an extremely thin absorber (eta) solar cell made with microporous TiO2/In(OH)xSy/PbS/PEDOT, an eta-solar cell of nanowire ZnO/CdSe/CuSCN, and a solid-state dye-sensitized solar cell (DSSC) with Spiro-OMeTAD as the transparent hole conductor. A negative capacitance behavior has been observed in all of them at high forward bias, independent of material type (organic and inorganic), configuration, and geometry of the cells studied. The experiments suggest a universality of the underlying phenomenon giving rise to this effect in a broad range of solar cell devices. An equivalent circuit model is suggested to explain the impedance and capacitance spectra, with an inductive recombination pathway that is activated at forward bias. The deleterious effect of negative capacitance on the device performance is discussed, by comparison of the results obtained for a conventional monocrystalline Si solar cell showing the positive chemical capacitance expected in the ideal IS model of a solar cell.
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PMID:Implications of the negative capacitance observed at forward bias in nanocomposite and polycrystalline solar cells. 1660 58

ZnO and ZnO:Zn powder phosphors were prepared by the polyol-method followed by annealing in air and reducing gas, respectively. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and photoluminescence (PL) and cathodoluminescence (CL) spectra, respectively. The results indicate that all samples are in agreement with the hexagonal structure of the ZnO phase and the particle sizes are in the range of 1-2 microm. The PL and CL spectra of ZnO powders annealed at 950 degrees C in air consist of a weak ultraviolet emission band (approximately 390 nm) and a broad emission band centered at about 527 nm, exhibiting yellow emission color to the naked eyes. When the sample was reduced at the temperatures from 500 to 1050 degrees C, the yellow emission decreased gradually and disappeared completely at 800 degrees C, whereas the ultraviolet emission band became the strongest. Above this temperature, the green emission ( approximately 500 nm) appeared and increased with increasing of reducing temperatures. According to the EPR results and spectral analysis, the yellow and green emissions may arise from the transitions of photogenerated electron close to the conduction band to the deeply trapped hole in the single negatively charged interstitial oxygen ion (Oi(-)) and the single ionized oxygen vacancy (V.O) centers, respectively.
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PMID:Tunable photoluminescent and cathodoluminescent properties of ZnO and ZnO:Zn phosphors. 1668 92

Stimulated emission was studied using time-integrated and time-resolved photoluminescence in ZnO comb, tetrapod, and rod nanostructures. All the measurements were performed on ensembles of the nanostructures. The nanostructures were fabricated by vapor deposition (combs, tetrapods) and hydrothermal methods (rods). While stimulated emission was detected in all of the nanostructures, significant differences in the behavior of the stimulated emission, as well as the lasing threshold power, were found for different morphologies. The differences in the time evolution of the lasing spectra were particularly pronounced. The observed differences in the stimulated emission spectra of the three types of nanostructures in both exciton-exciton scattering and electron-hole plasma regimes are discussed.
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PMID:Stimulated emission in ZnO nanostructures: A time-resolved study. 1685 83

The emission properties of nanocrystalline ZnO particles prepared following an organometallic synthetic method are investigated. Spherical particles and nanorods are studied. The shape of the particles and the ligands used are shown to influence the luminescence properties in the visible domain. Two different emissions are observed at 440 nm (approximately 2.82 eV) and at 580 nm (approximately 2.14 eV) that are associated with the presence of surface defects on the particles. The first emission corresponds to the well-known yellow emission located at 580 nm (approximately 2.14 eV) with a lifetime of 1850 ns for 4.0 nm size ZnO nanoparticles. The second emission at 440 nm (approximately 2.82 eV) is observed when amine functions are present. This strong blue emission is associated with an excitation energy less than that associated with the yellow emission displaying a lifetime of nine nanoseconds. A possible hole trapping effect by the amine groups on the surface of the ZnO particles is discussed as the origin of this emission. The modification of the intensities between the two visible emissions for different particle shapes is proposed to be related to a specific location of the amine ligands on the surface of the particles.
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PMID:Optical properties of zinc oxide nanoparticles and nanorods synthesized using an organometallic method. 1705 55

Luminescence of rare earth complex based on organic-inorganic heterostructure is reported. The structure of the device is ITO/PVK:Tb/inorganic material/Al, where inorganic material includes ZnS, ZnO or ZnSe. For this structure, the authors obtained the characteristic emission of Tb ion. A large part of driving voltage was dropped on the PVK layer because the dielectric constant of ZnS is 3 times bigger than that of PVK. The electric field strength in PVK layer was improved, so the velocity of hole in PVK was increased. The balance of injected charge was enhanced.
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PMID:[Luminescence of rare earth complex in organic-inorganic heterostructure]. 1705 32

Subnanometric ZnO clusters confined in different micropore zeolites are studied by steady-state and nanosecond time-resolved photoluminescence (PL) spectroscopy. The microsecond-scale lifetime is observed at room temperature for ZnO clusters confined in zeolites, which is significantly different from that of macrocrystalline ZnO on the external surface of zeolites. The dependence of luminescence lifetime on the amount of ZnO in zeolites indicates that the electron-phonon interactions between the ZnO clusters and the zeolite host significantly affect the dynamic relaxation process of ZnO clusters. The long lifetime luminescence of ZnO clusters can be achieved by weakening the coupling of electronic transition to zeolites host phonons. The similar long-lived luminescence is obtained when dispersing ZnO clusters into the porous SiO2. It is suggested that encapsulating the semiconductor cluster in the porous support is a possible way to inhibit or to retard the electron-hole recombination.
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PMID:Time-resolved photoluminescence characteristics of subnanometer ZnO clusters confined in the micropores of zeolites. 1718 Nov 97

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.
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PMID:Optical properties of ZnO nanostructures. 1719 49

The evolution of the gap of a nanoscaled insulator material, namely, Gd(2)O(3), has been observed by means of vacuum ultraviolet excitation spectra of a dopant (Eu(3+)). The nanoparticles have been synthesized by the low energy cluster beam deposition technique and grown afterward by different annealing steps. A gap shift towards the blue is observed, similar to what is observed in semiconductor nanoparticles. Despite the strong ionic character of the material, the evolution exhibits a behavior similar to covalent materials. The evolution of the gap for Gd(2)O(3) follows the same empiric rule that has been derived for semiconductors (ZnO, CuBr, Si, and CdS). It shows that, in spite of the strong ionic character of the material (0.9 on the scale of Phillips), the amount of covalency is important enough for creating a significant delocalization of the electron with regard to its hole.
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PMID:Quantum confinement effect on Gd2O3 clusters. 1728 87


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