Origin of luminescence from ZnO/CdS core/shell nanowire arrays

Nanoscale ◽  
2014 ◽  
Vol 6 (16) ◽  
pp. 9783-9790 ◽  
Author(s):  
Zhiqiang Wang ◽  
Jian Wang ◽  
Tsun-Kong Sham ◽  
Shaoguang Yang
Keyword(s):  
Optical Properties ◽  
Chemical Imaging ◽  
Nanowire Arrays ◽  
Nano Composites ◽  
Core Shell ◽  
Edge Structure ◽  
X Ray ◽  
Optical Luminescence ◽  
Scanning Transmission ◽  
X Ray Absorption

Chemical imaging, electronic structure and optical properties of ZnO/CdS nano-composites have been investigated using scanning transmission X-ray microscopy (STXM), X-ray absorption near-edge structure (XANES) and X-ray excited optical luminescence (XEOL) spectroscopy.

2D XANES-XEOL mapping: observation of enhanced band gap emission from ZnO nanowire arrays

Nanoscale ◽  
2014 ◽  
Vol 6 (12) ◽  
pp. 6531-6536 ◽  
Author(s):  
Zhiqiang Wang ◽  
Xiaoxuan Guo ◽  
Tsun-Kong Sham
Keyword(s):  
Band Gap ◽  
Nanowire Arrays ◽  
Zno Nanowire ◽  
Edge Structure ◽  
X Ray ◽  
Zno Nanowire Arrays ◽  
Optical Luminescence ◽  
Order Of Magnitude ◽  
X Ray Absorption ◽  
Mapping Observation

Using two-dimensional X-ray absorption near-edge structure-X-ray excited optical luminescence (2D XANES-XEOL) spectroscopy, it is found that the band gap emission of ZnO nanowire arrays is substantially enhancedi.e.that the intensity ratio between the band gap and defect emissions increases by more than an order of magnitude when the excitation energy is scanned across the O K-edge. Possible mechanisms are discussed.

Chemical and orientational imaging of polymeric samples

1994 ◽  
Vol 52 ◽  
pp. 68-69
Author(s):  
H. Ade ◽  
B. Hsiao ◽  
G. Mitchell ◽  
E. Rightor ◽  
A. P. Smith ◽  
...  
Keyword(s):  
Ethylene Terephthalate ◽  
National Laboratory ◽  
Brookhaven National Laboratory ◽  
Carbonyl Groups ◽  
Aromatic Rings ◽  
Edge Structure ◽  
X Ray ◽  
Scanning Transmission ◽  
Polymeric Samples ◽  
X Ray Absorption

We have used the Scanning Transmission X-ray Microscope at beamline X1A (X1-STXM) at Brookhaven National Laboratory (BNL) to acquire high resolution, chemical and orientation sensitive images of polymeric samples as well as point spectra from 0.1 μm areas. This sensitivity is achieved by exploiting the X-ray Absorption Near Edge Structure (XANES) of the carbon K edge. One of the most illustrative example of the chemical sensitivity achievable is provided by images of a polycarbonate/pol(ethylene terephthalate) (70/30 PC/PET) blend. Contrast reversal at high overall contrast is observed between images acquired at 285.36 and 285.69 eV (Fig. 1). Contrast in these images is achieved by exploring subtle differences between resonances associated with the π bonds (sp hybridization) of the aromatic groups of each polymer. PET has a split peak associated with these aromatic groups, due to the proximity of its carbonyl groups to its aromatic rings, whereas PC has only a single peak.

X-ray absorption spectroscopy and density functional analysis of the Fe3+ distribution profile on Al sites in a chrysoberyl crystal, BeAl2O4:Fe3+

2016 ◽  
Vol 49 (2) ◽  
pp. 385-388 ◽  
Author(s):  
Kanokwan Kanchiang ◽  
Atipong Bootchanont ◽  
Janyaporn Witthayarat ◽  
Sittichain Pramchu ◽  
Panjawan Thanasuthipitak ◽  
...  
Keyword(s):  
Optical Properties ◽  
Absorption Spectroscopy ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Distribution Profile ◽  
Laser Applications ◽  
Edge Structure ◽  
X Ray ◽  
Site Distribution ◽  
X Ray Absorption

Chrysoberyl is one of the most interesting minerals for laser applications, widely used for medical purposes, as it exhibits higher laser performance than other materials. Although its utilization has been vastly expanded, the location of transition metal impurities, especially the iron that is responsible for chrysoberyl's special optical properties, is not completely understood. The full understanding and control of these optical properties necessitates knowledge of the precise location of the transition metals inside the structure. Therefore, synchrotron X-ray absorption spectroscopy (XAS), a local structural probe sensitive to the different local geometries, was employed in this work to determine the site occupation of the Fe3+ cation in the chrysoberyl structure. An Fe K-edge X-ray absorption near-edge structure (XANES) simulation was performed in combination with density functional theory calculations of Fe3+ cations located at different locations in the chrysoberyl structure. The simulated spectra were then qualitatively compared with the measured XANES features. The comparison indicates that Fe3+ is substituted on the two different Al2+ octahedral sites with the proportion 60% on the inversion site and 40% on the reflection site. The accurate site distribution of Fe3+ obtained from this work provides useful information on the doping process for improving the efficiency of chrysoberyl as a solid-state laser material.

Soft X-ray excited colour-centre luminescence and XANES studies of calcium oxide

2007 ◽  
Vol 85 (10) ◽  
pp. 853-858 ◽  
Author(s):  
JY Peter Ko ◽  
Franziskus Heigl ◽  
Yun Mui Yiu ◽  
Xing-Tai Zhou ◽  
Tom Regier ◽  
...  
Keyword(s):  
Calcium Oxide ◽  
Density Functional ◽  
X Rays ◽  
Colour Centre ◽  
Time Resolved ◽  
Edge Structure ◽  
Colour Centres ◽  
X Ray ◽  
Optical Luminescence ◽  
X Ray Absorption

In this study, we show that colour centres can be produced by irradiating calcium oxide with soft X-rays from a synchrotron radiation source. Using the X-ray excited optical luminescence (XEOL) technique, two colour centres, F-centre, and F+-centre can be identified. These colour centres emit photons at characteristic wavelengths. In addition, by performing time-resolved XEOL (TRXEOL), we are able to reveal timing and decay characteristics of the colour centres. We also present X-ray absorption near-edge structure (XANES) spectra collected across oxygen K-edge, calcium L3,2-edge, and calcium K-edge. Experimental results are compared with density functional theory (DFT) calculations.Key words: calcium oxide, colour centre, synchrotron, X-ray excited optical luminescence, X-ray absorption near-edge structure.

Microstructure and electronic behavior of PtPd@Pt core-shell nanowires

2010 ◽  
Vol 25 (4) ◽  
pp. 711-717 ◽  
Author(s):  
Wei-Qiang Han ◽  
Dong Su ◽  
Michael Murphy ◽  
Matthew Ward ◽  
Tsun-Kong Sham ◽  
...  
Keyword(s):  
Shell Structure ◽  
Phase Transfer ◽  
Core Shell ◽  
Face Centered Cubic ◽  
Edge Structure ◽  
X Ray ◽  
One Step ◽  
Core Shell Structure ◽  
Face Centered ◽  
X Ray Absorption

PtPd@Pt core-shell ultrathin nanowires were prepared using a one-step phase-transfer approach. The diameters of the nanowires range from 2 to 3 nm, and their lengths are up to hundreds of nanometers. Line scanning electron energy loss spectra showed that PtPd bimetallic nanowires have a core-shell structure, with a PtPd alloy core and a Pt monolayer shell. X-ray absorption near edge structure (XANES) spectra reveal that a strong Pt-Pd interaction exists in this nanowire system in that there is PtPd alloying and/or interfacial interaction. Extended x-ray absorption fine structures (EXAFS) further confirms the PtPd@Pt core-shell structure. The bimetallic nanowires were determined to be face-centered cubic structures. The long-chain organic molecules of n-dodecyl trimethylammonium bromide and octadecylamine, used as surfactants during synthesis, were clearly observed using aberration-corrected TEM operated at 80 KV. The interaction of Pt and surfactants was also revealed by EXAFS.

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