• Korean Journal of Materials Research
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• v.24 no.7
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• pp.351-356
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• 2014

A spherical $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor for use in white-light-emitting diodes was synthesized using a liquid-state reaction with two precipitation stages. For the formation of phosphor from a precursor, the calcination temperature was $1,100^{\circ}C$. The particle morphology of the phosphor was changed by controlling the processing conditions. The synthesized phosphor particles were spherical with a narrow size-distribution and had mono-dispersity. Upon excitation at 395 nm, the phosphor exhibited an emission band centered at 497 nm, corresponding to the $4f^65d{\rightarrow}4f^7$ electronic transitions of $Eu^{2+}$. The critical quenching-concentration of $Eu^{2+}$ in the synthesized $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor was 5 mol%. A phosphor-converted LED was fabricated by the combination of the optimized spherical phosphor and a near-UV 390 nm LED chip. When this pc-LED was operated under various forward-bias currents at room temperature, the pc-LED exhibited a bright blue-green emission band, and high color-stability against changes in input power. Accordingly, the prepared spherical phosphor appears to be an excellent candidate for white LED applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.279.2-279.2
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• 2016

InGaN/GaN multiple quantum wells (MQWs) have been attracted much attention as light-emitting diodes (LEDs) in the visible and UV regions. Particularly, quantum efficiency of green LEDs is decreased dramatically as approaching to the green wavelength (~500 nm). This low efficiency has been explained by quantum confined Stark effect (QCSE) induced by piezoelectric field caused from a large lattice mismatch between InGaN and GaN. To improve the quantum efficiency of green LED, several ways including epitaxial lateral overgrowth that reduces differences of lattice constant between GaN and sapphire substrates, and non-polar method that uses non- or semi-polar substrates to reduce QCSE were proposed. In this study, graded short-period InGaN/GaN superlattice (GSL) was grown below the 5-period InGaN/GaN MQWs. InGaN/GaN MQWs were grown on the patterned sapphire substrates by vertical-metal-organic chemical-vapor deposition system. Five-period InGaN/GaN MQWs without GSL structure (C-LED) were also grown to compare with an InGaN/GaN GSL sample. The luminescence properties of green InGaN/GaN LEDs have been investigated by using photoluminescence (PL) and time-resolved PL (TRPL) measurements. The PL intensities of the GSL sample measured at 10 and 300 K increase about 1.2 and 2 times, respectively, compared to those of the C-LED sample. Furthermore, the PL decay of the GSL sample measured at 10 and 300 K becomes faster and slower than that of the C-LED sample, respectively. By inserting the GSL structures, the difference of lattice constant between GaN and sapphire substrates is reduced, resulting that the overlap between electron and hole wave functions is increased due to the reduced piezoelectric field and the reduction in dislocation density. As a results, the GSL sample exhibits the increased PL intensity and faster PL decay compared with those for the C-LED sample. These PL and TRPL results indicate that the green emission of InGaN/GaN LEDs can be improved by inserting the GSL structures.

• Korean Journal of Medicinal Crop Science
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• v.12 no.3
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• pp.179-182
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• 2004

Bioassay-directed fractionation of the dried roots of Salvia miltiorrhiza led to the isolation of abietane tanshinones, cryptotanshinone and dibydrotanshinone I. Their structures were elucidated using $^1H-\;and\;^{13}C-NMR$, UV, IR and mass spectral analyses. These compounds exhibited a moderate antimicrobial activities against Staphylococcus epidemidis, Staphylococcus aureus, and Staphylococcus pyogene.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.173-173
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• 2003

Nanowire와 nanorod 같은 1차원의 반도체 재료는 디멘젼과 크기와 물리적 특성과의 관계 등을 연구하는데 중요한 역할을 하며 laser ablation, arc discharge, chemical vapor depostion, vapor phase transport Process와 solution등의 방법으로 성공적으로 합성되었다. ZnO 는 3.37eV의 넓은 밴드갭과 다른 넓은 밴드갭 재료에 비해 높은 exciton bindng energy (60meV)를 가지며 UV LED, laser diode에 적용하기 유리하고 최근 디스플레나 나노 광전소자로서의 가능성 이 대두되면서 최근 이에 관한 연구가 증가하고 있다. 본 연구에서는 열적탄소환원법(carbothermal reduction process)으로 ZnO와 graphite 분말을 1:1 중량비로 혼합한 분말을 90$0^{\circ}C$, 100$0^{\circ}C$에서 air 분위기에서 20분간 반응 후 로 내에서 냉각 하였다. 직경 이 50nm-1000nm, 길이가 수 미크론인 내부 결함이 전혀 없는 육각형 단결정의 nanowire가 합성되었고 XRD, FE-SEM과 TEM으로 조성 및 형상, 내부구조를 분석하였다. 합성된 ZnO nanowire는 직경 이 변하는 부분에서 성장방향으로의 계단을 형성하였고 이는 layer by layer 방법으로 nanowire가 성장한다는 것을 나타낸다.

• Elastomers and Composites
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• v.59 no.1
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• pp.1-7
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• 2024

Nanorod graphitic carbon nitride (g-C₃N₄) was synthesized by reacting melamine (C₃H₆N₆) with trithiocyanuric acid (C₃H₃N₃S₃) in distilled water for 10 h at room temperature. The resulting mixture was calcined at 550℃ for 2 h in an electric furnace under an air atmosphere. Nanorod g-C₃N₄/Ag₃PO₄ composites were prepared by adding nanorod graphitic carbon nitride (g-C₃N₄) powder, silver nitrate (AgNO₃), ammonia (NH₃·H₂O, 25.0-30.0%), and sodium hydrogen phosphate (Na₃HPO₄) to distilled water. The samples were characterized via X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The photocatalytic activities of the nanorod g-C₃N₄/Ag₃PO₄ composites were demonstrated via the degradation of organic dyes, such as methylene blue and methyl orange, under blue light-emitting diode irradiation and evaluated using UV-vis spectrophotometry.

• Journal of Environmental Science International
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• v.21 no.5
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• pp.563-572
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• 2012

Unlike water applications, the photocatalytic technique utilizing light-emitting-diodes as an alternative light source to conventional lamp has rarely been applied for low-level indoor air purification. Accordingly, this study investigated the applicability of UV-LED to annular-type photocatalytic reactor for removal of indoor-level benzene and toluene at a low concentration range associated with indoor air quality issues. The characteristics of photocatalyst was determined using an X-ray diffraction meter and a scanning electron microscope. The photocatalyst baked at $350^{\circ}C$ exhibited the highest photocatalytic degradation efficiencies(PDEs) for both benzene and toluene, and the photocatalysts baked at three higher temperatures(450, 550, and $650^{\circ}C$) did similar PDEs for these compounds. The average PDEs over a 3-h period were 81% for benzene and close to 100% for toluene regarding the photocatalyst baked at $350^{\circ}C$, whereas they were 61 and 74% for benzene and toluene, respectively, regarding the photocatalyst baked at $650^{\circ}C$. As the light intensity increased from 2.4 to 3.5 MW $cm^{-1}$, the average PDE increased from 36 to 81% and from 44% to close to 100% for benzene and toluene, respectively. In addition, as the flow rate increased from 0.1 to 0.5 L $min^{-1}$, the average PDE decreased from 81% to close to zero and from close to 100% to 7% for benzene and toluene, respectively. It was found that the annular-type photocatalytic reactor inner-inserted with UV-LEDs can effectively be applied for the decomposition of low-level benzene and toluene under the operational conditions used in this study.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.19 no.1
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• pp.57-76
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• 1993

Phototoxicity is a complex phenomenon which may involve photochemical reaction and biological response mechanism. This complexicity and iii mal protecting tendency has led to the development of various in-vitro approaches as sensitive, alternative test to the in-vivo phototoxicity test. In this study, we investigated not only the sensitivity of two microorganism, (C. albicans and 5. typhimurium TA 98 about UV) but also a correlation between in-vitro and in-vivo phototoxicity test using UV A and 1 Furthermore, we studied the effect of irradiation method which were as follows 1) irradiate to material and microorganism, simultaneously 2) irradiate to only material 3) irradiate to material and microorganism, respectively In each irradiation method, it showed no significant difference, However we were able to observe the more sensitive phototoxicity in S. typhimurium TA 98 than C. albicans, and the results of in-vitro test using 5. typhimurium TA 98 had a good correlation with those of in-vivo test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.145-146
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• 2006

The most Important research topic in the development of ZnO LED and LD is the production of p-type ZnO thin film that has minimal stress with outstanding stoichiometric ratio. In this study, Phosphorus diffused into the undoped ZnO thin films using the ampoule-tube method for the production of p-type znO thin films. The undoped ZnO thin films were deposited by RF magnetron sputtering system on $GaAs_{0.6}P_{0.4}$/GaP and Si wafers. 4N Phosphorus (P) was diffused into the undoped ZnO thin films in ampoule-tube which was performed and $630^{\circ}C$ during 3hr. We found the diffusion condition of the conductive ZnO films which had p-type properties with the highest mobility of above 532 $cm^2$/Vs compared with other studies PL spectra measured at 10K for the purpose of analyzing optical properties of p-type ZnO thin film showed strong PL intensity in the UV emission band around 365nm ~ 415nm and 365nm ~ 385nm.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.277-277
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• 2017

The research was carried out to investigate a total polyphenol content, antioxidant activity, amino acid and resveratrol content of peanut sprouts (cotyledon, epicotyl, leaf, hypocotyl, root), in different light (white, blue, red, F-red, UV-A, UV-B, UV-C) conditions for 24 hours. Peanut seeds were sown on a $27.5{\times}15.9{\times}13cm$ tray and grown at the $25^{\circ}C$ under the dark condition for 14 days. Total polyphenolic contents of epicotyl and leaf were about 288mg GAE/100g in blue light. The DPPH radical scavenging of cotyledon and hypocotyl were 1.3~1.5 times (63%) and 2 times (40%) compared to control (43%, 19%), respectively. As to ABTS activity, its activity was increased by all LEDs treatment, Especially, the highest ABTS activity of the hypocotyl and leaf was shown as 99.1% in blue light. The essential amino acid content of hypocotyl and leaf was increased 1.9 times in the UV-B, 1.6 times in red, and 1.5 times in F-red, respectively. The non-essential amino acid content was increased by all LEDs treatment in hypocotyl and leaf. The content of resveratrol was increased by 1.3 times in UV-B compared to that of other tissues. Assessing inclusively, this study showed that there was a significantly positive effect between increase of physiological substance activity and LED light treatment, resulting in stably producing peanut sprouts. Therefore, a material treated with LEDs is thought to be useful as a functional food resources.

• Textile Coloration and Finishing
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• v.30 no.2
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• pp.63-69
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• 2018

In this study, we report on successful attempt towards the synthesis of sulfur self-doped $g-C_3N_4$ by directly heating thiourea in air. The synthesized materials were characterized using UV-vis spectral technique, FT-IR, XRD and TEM analysis. Further, the obtained material shows an excellent detection of carcinogenic TNP(Tri nitro phenol) in the presence of 10-fold excess of various other common interferences. The strong inner filter effect and molecular interactions(electrostatic, ${\pi}-{\pi}$, and hydrogen bonding interactions) between TNP and the $S-g-C_3N_4$ Nano sheets led to the fluorescence quenching of the $S-g-C_3N_4$ Nano sheets with an excellent selectivity and sensitivity towards TNP compared to that of other nitro aromatics under optimal conditions and the detection limit calculated was found to be 6.324 nM for TNP. The synthesized nanocomposite provides a promising platform for the development of sensors with improved reproducibility and stability for ultra-sensitive and selective sensing of TNP.