• Korean Journal of Materials Research
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• v.18 no.11
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• pp.623-627
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• 2008

For possible applications as luminescent materials for white-light emission using UV-LEDs, $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphors were prepared by a solid state reaction. The photoluminescence properties of the phosphor were investigated under ultraviolet ray (UV) excitation. The prepared phosphor powders were characterized to from a single phase of a monoclinic crystalline structure by a powder X-ray diffraction analysis. In the photoluminescence spectra, the $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphor showed an intense emission band centered at the 584 nm wavelength due to the f-d transition of the $Eu^{2+}$ activator. The optimum concentration of $Eu^{2+}$ activator in the $Ba_2Mg(PO_4)_2$ host, indicating the maximum emission intensity under the excitation of a 395 nm wavelength, was 5 at%. In addition, it was confirmed that the $Eu^{2+}$ ions are substituted at both $Ba^{2+}$ sites in the $Ba_2Mg(PO_4)_2$ crystal. On the other hand, the critical distance of energy transfer between $Eu^{2+}$ ions in the $Ba_2Mg(PO_4)_2$ host was evaluated to be approximately 19.3 A. With increasing temperature, the emission intensity of the $Ba_2Mg(PO_4)_2$:Eu phosphor was considerably decreased and the central wavelength of the emission peak was shifted toward a short wavelength.

• Journal of the Korean institute of surface engineering
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• v.47 no.4
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• pp.204-209
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• 2014

The electrodeposition of ZnO nanorods was performed on ITO glass. The optimization of two process parameters (solution temperature and growth time) has been studied in order to control the orientation, morphology, density, and growth rate of ZnO nanorods. The structural and optical properties of ZnO nanorods were systematically investigated by using field-emission scanning electron microscopy, X-ray diffractometer, and photoluminescence. Commonly, the results of the structural property show that hexagonal ZnO nanorods with wurtzite crystal structures have a c-axis orientation, and higher intensity for the ZnO (002) diffraction peaks. Furthermore, the nanorods length increased with increasing both the solution temperature and the growth time. The results of the optical property show a strong UV (3.28 eV) peaks and a weak visible (1.9~2.4 eV) bands, the intensity of UV peaks was increased with increasing both the solution temperature and the growth time. Especially, the UV peak for growth of nanorods at $75^{\circ}C$ blue-shift than different temperatures.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.353-353
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• 2011

Titanium dioxide is a suitable material for industrial use at present and in the future because titanium dioxide has efficient photoactivity, good stability and low cost [1]. Among the three phases (anatase, rutile, brookite) of titanium dioxide, the anatase form is particularly photocatalytically active under ultraviolet (UV) light. In fabrication of photocatalytic devices based on catalytic nanodiodes [2], it is challenging to obtain a photocatalytically active TiO2 thin film that can be prepared at low temperature (< 200$^{\circ}C$). Here, we present the synthesis of a titanium dioxide film using TiO2 nanoparticles and sol-gel methods. Titanium tetra-isopropoxide was used as the precursor and alcohol as the solvent. Titanium dioxide thin films were made using spin coating. The change of atomic structure was monitored after heating the thin film at 200$^{\circ}C$ and at 350$^{\circ}C$. The prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microcopy, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible spectroscopy (UV-vis), and ellipsometry. XRD spectra show an anatase phase at low temperature, 200$^{\circ}C$. UV-vis confirms the anatase phase band gap energy (3.2 eV) when using the photocatalyst. TEM images reveal crystallization of the titanium dioxide at 200$^{\circ}C$. We will discuss the switching behavior of the Pt /sol-gel TiO2 /Pt layers that can be a new type of resistive random-access memory.

• Journal of the Korean Applied Science and Technology
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• v.33 no.1
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• pp.13-22
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• 2016

This study set its purpose on to specify whether it is possible to use wheat sprout extracts for source of cosmetics, and its biological activity. Cellular experiment was conducted to apprehend toxicity of wheat sprout extracts and through study on the whitening and aging activity of skin cell. As a result, it is appeared that wheat sprout extracts have weak toxicity for HDF, B16F10 cells. Also, it is appeared that wheat sprout extracts have weak deterrent effect on melanin biosynthesis, but since the extracts impede expression of MMP-1, which is induced UV ray, the extracts hold down the aging effect by UV rays. Hence the extracts are effective on preventing wrinkles caused by UV ray and aging. Therefore, this study is expected to be utilized usefully, if the wheat sprout extracts are used as source of functional cosmetics from the perspective of preventing skin-aging in the future.

• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.738-745
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• 2015

The catalytic exchange of hydrogen isotopes between hydrogen and water has been known to be a very useful process for the separation of tritium from tritiated water. For the process, a highly active hydrophobic catalyst is needed. This study provides an effective fabrication method of size-controlled platinum/poly[styrene-divinylbenzene-tri(propylene glycol) diacrylate] [Pt/poly(SDB-TPGDA)] hydrophobic catalyst beads with a narrow size distribution. Platinum nanoparticles were prepared by ${\gamma}$-ray-induced reduction in the aqueous phase first, and then uniformly dispersed in SDB-TPGDA comonomer after the hydrophobization of platinum nanoparticles with alkylamine stabilizers. The porous Pt/poly(SDB-TPGDA) hydrophobic catalyst beads were synthesized by the UV-initiated polymerization of the mixture droplets prepared in a capillary-based microfluidic system. The size of as-prepared catalyst beads can be controlled in the range of $200-1,000{\mu}m$ by adjusting the flow rate of dispersed and continuous phases, as well as the viscosity of the continuous phase. Sorbitan monooleate and cyclohexanol were used as coporogens to control the porosities of the catalyst beads.

• Korean Journal of Chemical Engineering
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• v.35 no.11
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• pp.2283-2289
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• 2018

$TiO_2$ microspheres were successfully synthesised by simple solution phase method by using various amount of titanium butoxide as precursor. The prepared $TiO_2$ were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance absorption spectra (UV-DRS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XRD analysis revealed that the as-synthesized $TiO_2$ microsphere poses an anatase phase. The photocatalytic degradation experiments were carried out with three different dyes, such as methylene blue, brilliant black, reactive red-120 for four hours under UV light irradiation. The results show that $TiO_2$ morphology had great influence on photocatalytic degradation of organic dyes. The experimental results of dye mineralization indicated the concentration was reduced by a high portion of up to 99% within 4 hours. On the basis of various characterization of the photocatalysts, the reactions involved to explain the photocatalytic activity enhancement due to the concentration of titanium butoxide and morphology include a better separation of photogenerated charge carriers and improved oxygen reduction inducing a higher extent of degradation of aromatics.

• Clean Technology
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• v.16 no.1
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• pp.46-50
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• 2010

This study focuses on the removal of water-suspended toluene of a representative sick house compounds in a liquid photo-system using nanometer-sized Sn-incorporated $TiO_2$ which was synthesized by a solvothermal method. The characteristics of the synthesized Sn-$TiO_2$ were analyzed by X-ray Diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), and UV-visible spectroscopy (UV-Vis). To estimate the photocatalytic activity of Sn-$TiO_2$, the photodegradation of water-suspended toluene was performed, and the remaining concentration was determined using UV-visible spectroscopy. The water-suspended toluene photodegradation over Sn-incorporated $TiO_2$ catalyst was better than that over pure $TiO_2$ (anatase). The water-suspended toluene of 500 ppm was perfectly decomposed within 300 minutes over 0.01 mol% Sn-$TiO_2$.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.64.2-64.2
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• 2019

HD 81817 is known as a hybrid star. Hybrid stars have both cool stellar wind properties and UV or even X-ray emission features of highly ionized atoms in their spectra. A white dwarf companion has been suggested as the source of UV or X-ray features. HD 81817 has been observed since 2004 as a part of our radial velocity (RV) survey program to search for exoplanets around K giant stars using the Bohyunsan Observatory Echelle Spectrograph (BOES) at the 1.8 m telescope of Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We obtained 84 RV measurements between 2004 and 2018 for HD 81817 and found two periodic RV variations. The obtained amplitudes of RV periods are around 200 m/s, which are significantly lower than that expected from a white dwarf companion. Furthermore, our re-analysis of the IUE spectra used by Reimers (1984) shows that the excess in UV emission can easily be explained by a pseudo-continuum of unresolved emission lines originating in the extended chromosphere of the star. We thus conclude that there are no companions of stellar mass to HD 81817. Meanwhile, we analyzed two periodicities in RV measurements and conclude that the period of 627.9 days is caused by intrinsic stellar activities based on H alpha equivalent width (EW) variations of a similar period. On the other hand, the period of 1047.8 days is likely to be caused by substellar companion which has a minimum mass of 27.6 M_JUP, a semi-major axis of 3.3 AU, and an eccentricity of 0.17 assuming the stellar mass of 4.3 M_⊙ for HD 81817. The inferred mass puts HD 81817 b in the brown dwarf desert.

• Particle and aerosol research
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• v.12 no.2
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• pp.37-42
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• 2016

$CeO_2$ nanoparticles were prepared by a flame spray pyrolysis from aqueous solution of cerium nitrate. The morphology, structure crystallinity and specific surface area of as-prepared nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Telle (BET). The $CeO_2$ nanoparticles about 5 nm in diameter showed a cubic fluorite structure and polyhedral morphology. The average particle size increased as the cerium nitrate concentration increased. UV absorption performance of the as-prepared nanoparticles was measured by UV-visible spectroscopy. UV absorption of $CeO_2$ nanoparticles was more effective than that of commercial $TiO_2$ nanoparticles. Effect of dopants such as Ti and Zn to $CeO_2$ nanoparticles on UV absorption properties was also investigated. In case of $Ti/CeO_2$, and $Zn/CeO_2$ nanoparticles, they showed a little higher UV absorption values compared with $CeO_2$ nanoparticles. The as-prepared nanoparticles can be promising materials with high UV absorption value.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.273-276
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• 2011

Ultraviolet (UV) light emitting diodes (LEDs) were grown on a patterned n-type GaN substrate (PNS) with 200 nm silicon-di-oxide (SiO2) nano pattern diameter to improve the light output efficiency of the diodes. Wet etched self assembled indium tin oxide (ITO) nano clusters serve as a dry etching mask for converting the SiO2 layer grown on the n-GaN template into SiO2 nano patterns by inductively coupled plasma etching. PNS is obtained by n-GaN regrowth on the SiO2 nano patterns and UV-LEDs were fabricated using PNS as a template. Two UV-LEDs, a reference LED without PNS and a 200 nm PNS UV-LEDs were fabricated. Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) and Light output intensity- Input current- Voltage (L-I-V) characteristics were used to evaluate the ITO-$SiO_2$ nanopattern surface morphology, threading dislocation propagation, PNS crystalline property, PNS optical property and UVLED device performance respectively. The light out put intensity was enhanced by 1.6times@100mA for the LED grown on PNS compared to the reference LED with out PNS.