Stimulated luminescence of ZnO nanocrystals of different shape grown by the method of gas transport (original) (raw)
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Journal of Physical Chemistry B, 2005
Nanocrystals of the wide band gap semiconductor zinc oxide of controllable morphologies were synthesized by a simple thermal decomposition method. The predominating factor in determining the morphology (spheres, triangular prisms, and rods) was the solvent, selected on the basis of coordinating power. The nanoparticles were structurally analyzed, and the photoluminescence of each shape was compared. The intensity of the green band emission, common to many ZnO structures, was found to vary with morphology. The strongest green band intensity corresponded to the shape with the largest surface/volume ratio and could be attributed to surface oxygen vacancies. Control over the morphology of ZnO at the nanoscale is presented as a means to control the green band emission.
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Japanese Journal of Applied Physics, 2008
We report on the optical modulation of ultraviolet (UV) photoluminescence from ZnO nanocrystals excited by He-Cd laser (325 nm) with visible Ar þ laser radiation (488 nm). The effective reversible quenching of the UV luminescence intensity was achieved. The quenching efficiency was found to depend on temperature, the ratio of He-Cd and Ar þ laser intensities, and the frequency of modulation.
Visible Luminescence from ZnO Nanostructures
MRS Proceedings, 2006
ABSTRACTRoom temperature photoluminescence (PL) spectra from zinc oxide (ZnO) nanostructures were studied. ZnO samples were produced via thermal chemical vapor deposition (thermal-CVD) and a variety of ZnO nanostructures were synthesized by adjusting the oxygen content during the growth process. All samples exhibit a sharp and strong ultra-violet near-band-edge (NBE) emission at about 3.18 eV. The visible emission from the samples deposited under an oxygen-deficient condition were dominated by blue-green band emission at 2.34 eV. The intensity of the blue-green band was greatly reduced (so-called green band free) for the ZnO deposited at the center of the wafer while strong violet-blue emission bands and broad bands at yellow-orange-red range were collected from the ZnO grown along the edge of the wafer. We believe that the spatial inhomogeniety was caused by turbulent gas flow in the reaction chamber, which resulted in different local oxygen concentration. Origin of visible lumines...
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The luminescence of ZnO nanocrystals prepared by different methods was studied under pulsed electron beam excitation. It is shown that the luminescence intensity depends on the nanocrystal sintering conditions and does not depend on the nanocrystal size within the range 10-50 nm. The relative luminescence intensities for the 3.32 eV (free exciton) and ∼3.20 eV (bound exciton) bands showed a dependence on nanocrystal size. The role of the nanocrystal surface in excitonic luminescence is discussed.
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International Nano Letters, 2012
ZnO is a promising member of the semiconducting materials of II-VI group. ZnO nanocrystals have shown potential applications in various novel technologies. In the present investigation of ZnO nanocrystals, a novel chemical route using Zinc acetate as organic precursor is being reported. ZnO nanocrystals were characterized using X-ray diffraction, scanning electron microscopy UV-visible (UV–vis) spectroscopy, and photoluminescence measurements. The X-ray diffraction studies reveal the typical hexagonal structure of ZnO nanocrystals along the preferred orientation of (101) and (100) planes. The optical bandgap of ZnO nanocrystals was found to be 3.50 eV from the absorbance spectrum, which is higher than that of the bulk ZnO material. A blueshift of 21 nm is observed in the excitonic transitions, which clearly indicates the formation of ZnO nanocrystals. Photoluminescence spectroscopy of the ZnO nanocrystals showed a strong emission peak at 365 nm near the band edge along with a weak g...
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ZnO nanocrystals grown by chemical solution deposition were studied by means of photoluminescence and cathodoluminescence spectroscopy. A postgrown annealing treatment significantly improved the UV emission efficiency and resulted in the clear appearance of a low temperature emission band around 3.31 eV (so-called A-line). Spatially and wavelength resolved cathodoluminescence measurements revealed a spotlike distribution of the A-line emission on a nanocrystal surface. It is found that there is a strong correlation between the emission around 3.31 eV and the specklike defects on the nanocrystal surface that appeared after annealing. The origin of the A-line and the specklike defects are discussed.
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An adapted form of vapor transport is used for the preparation of zinc oxide (ZnO) nanostructures. Control of substrate, partial pressure, temperature, and deposition time enable the synthesis of seven ZnO samples, each with different morphology. Characterization by X-ray diffraction (XRD), photoluminescence spectroscopy (PLS), and scanning electron microscopy (SEM) shows ZnO forms with a wide range of microstructures such as ''nano-stars'', ''nano-caterpillars'', urchin-like structures, and vertically aligned forests of hexagonal nanorods. Adopting a systematic approach of varying a single parameter from the standard experimental method, enables an understanding of why the resultant morphologies are obtained. In particular, a growth mechanism is proposed whereby hexagonal crystals grow from the catalytic substrate consisting of gold droplets, close to, or at, the melting temperature, supersaturated with zinc and oxygen, allowing propagation of hexagonal ''parent'' pillars. Parent pillars then form ''daughter'' rods which propagate sideways from the faces with angles tending towards 608 from each other.
MRS Proceedings, 2006
ABSTRACTZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies showed that ZnO nanorods grew mostly perpendicularly to the GaN substrate surface, whereas a more random directional distribution was found for nanorods on Si. Optical properties of fabricated nanorods were studied by steady-state photoluminescence and time-resolved photoluminescence. Stimulated emission was observed from ZnO nanorods on GaN substrates. Raman spectroscopy revealed biaxial strain in the nanorod samples grown on Si. Conductive atomic force microscopy was applied to study I-V spectra of individual nanorods.
By this report, we described the facile synthesis technique for the synthesis of hexagonal prism and rod like ZnO nanostructures via simple refluxing route by varying the hexamethylenetetramine and refluxing time. The microstructural parameters such as unit cell volume, bond length, dislocation density and microstrain were extracted from the X-ray diffraction data analysis. The variation in size, shape and morphological details of the prepared nanostructures were discussed using the scanning electron microscope and transmission electron microscope images. The effect of precursors concentration ratio and variation in refluxing time, which played a significant role on the formation of ZnO nanostructures, on the tunability of the aspect ratio was discussed. Also, in relation with these parameters the variation of the band gap and the intensity of (photo luminescence) emission of the nano ZnO was discussed. The obtained results revealed that the microstructural parameters, band gap and luminescence are highly depending on the aspect ratio and the morphology of the ZnO nanostructures. The variation of phonon modes with crystallinity and the phonon life time of the prepared nanostructures were discussed with the Raman spectral data analysis. The photocatalytic activity of the prepared nanostructures with different morphology (prism, rod and bipods) was monitored.
Thermolytic Growth of ZnO Nanocrystals: Morphology Control and Optical Properties
Crystal Growth & Design, 2009
ZnO nanostructures with triangular and rod-like morphologies could be grown by thermolysis of zinc acetate in oleylamine solvent using oleic acid as surfactant. Concentration of the zinc precursor in the reaction mixture had a strong effect on the final morphology of the ZnO nanostructures. While a low precursor concentration results in triangular morphology, high precursor concentrations favor rod-like morphologies of the nanostructures. The room temperature photoluminescence (PL) spectra of both nanostructures are dominated by the green emission attributed to the oxygen vacancy (V O ) related donor-acceptor transition. Presence of several infrared (IR) inactive vibrational modes in the Fourier transform infrared (FT-IR) absorption spectra of the samples indicates a breakdown of translational symmetry in the nanostructures induced by native defects. Possible mechanisms of the morphology evolution and the origin of observed visible emissions in the nanostructures are discussed.