• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.218-224
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• 1998

2nO and $Al_{2}O_{3}$ powder were weighed in 1 : 1 mole ratio and ball-milled in ethanol for 3 h. Dried mixture were pressed and then sintered at $900^{\circ}C{\sim}1200^{\circ}C$ for 3 h in vacuum($3{\times}10^{-5}$ Torr). According to XRD, remnant ZnO and $Al_{2}O_{3}$ not converted to $ZnAl_{2}O_{4}$ were observed up to $1100^{\circ}C$, which were completely changed to$ZnAl_{2}O_{4}$ ternary compound at $1200^{\circ}C$. Optical bandgap is calculated at 4.75 eV. With increasing sintering temperature, PL spectrums shifted to shorter wavelengths and are appeared 430nm at $1200^{\circ}C$.

• Journal of the Korean Chemical Society
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• v.20 no.5
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• pp.398-405
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• 1976

A new compound, 1,2-bispyrazyl ethylene,is synthesized starting from pyrazine carboxylic acid and methyl pyrazine. The compound is characterized utilizing UV-VIS, IR, NMR and mass spectra along with elemental analysis. Spectroscopic properties are studied from UV-VIS and fluorescence spectra. From unusual salt effects on fluorescence spectra, it is believed that $(n,\;{\pi}^*)$ state has about the same energy as $({\pi},\;{\pi}^*)$ state. The compound fluoresces from $({\pi},\;{\pi}^*)$ state with the quantum yield of 0.025 at $77^{\circ}K$ compared to near unity for stilbene at the same temperature indicating the efficient intersystem crossing to triplet state, because of strong $(n,\;{\pi}^*)$ and $({\pi},\;{\pi}^*)$ mixing in the lowest excited state.

• Journal of the Korean Chemical Society
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• v.36 no.3
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• pp.405-411
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• 1992

The substitution reaction and structrue of products obtained from the reaction of Equatorial-Skew-[Co(TRDTRA)($OH_2$)] (TRDTRA = trimethylenediaminetriacetate) with $CN^-, NO^{-}_{2}$ and $NCS^-$ ions have been investigated by means of electronic absorption spectroscopy and theoretical calculation based on the Yamatera's theory. According to kinetic data, the substitution reaction order for the complexes such as $CN^-, NO^{-}_{2}$ and $NCS^-$ was the first order, respectively, and overall reaction order was second order. It has been determined that the structure of products having $CN^{-} and NO^{-}_{2}$ ions was Polar-Chair type complexes which were accompanying with isomerization and having $NCS^-$ ion was Equatorial-Skew type complex which was not accompanying with isomerization.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.71-74
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• 2019

In this study, we fabricated two standard and inverted quantum dot light emitting diodes (QLEDs) using $TiO_2$ nanoparticles (NPs) with lower electron mobility than ZnO NPs as inorganic electron transport layer to suppress electron injection into the emitting layer. Current density was much higher for the inverted QLEDs than the standard ones. The inverted QLEDs were brighter, but showed low current efficiency due to the high current density. In addition, as the current density was higher, the driving voltage was higher, and the red shift was confirmed in the emission wavelength spectrum. The low current density in the standard structured devices showed that the possibility that $TiO_2$ NPs could suppress the electron injection in the QLEDs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.155-162
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• 2006

This study presents the seismic risk assesment for an extradosed bridge with seismic isolators of lead rubber bearings(LRB). First, the seismic vulnerability of a structure and then the seismic hazard of the site are evaluated using earthquake data set and seismic hazard map in Korea, and then the seismic risk of the structure is assessed. The nonlinear seismic analyses are carried out to consider plastic hinges of bridge columns and nonlinear characteristics of soil foundation. The ductility demand is adopted to describe the nonlinear behavior of a column, and the moment-curvature curve of a column is assumed to be bilinear hysterestic. The fragility curves are represented as a log-normal distribution function for column damage, movement of superstructure, and cable yielding. And seismic hazard is estimated using the available seismic hazard maps. The results show that the effectiveness of the seismic isolators for the columns is more noticeable than those for cables and girders, in seismic isolated extradosed bridges under earthquakes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.6
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• pp.425-433
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• 2000

The stochiometric mix of evaporating materials for the $CuGaTe_2$single crystal thin films was prepared from horizontal furnance. Using extrapolation method of X-ray diffraction patterns for the $CuGaTe_2$polycrystal, it was found tetragonal structure whose lattice constant $a_0 and c_0$ were 6.025 $\AA$ and 11.931 $\AA$, respectively. To obtain the single crystal thin films, $CuGaTe_2$mixed crystal was deposited on throughly etched semi-insulator GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $670^{\circ}C$ and $410^{\circ}C$ respectively, and the thickness of the single crystal thin films is 2.1$\mu\textrm{m}$. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). Hall effect on this sample was measured by the method of van der Pauw and studied on carrier density and mobility dependence on temperature. The carrier density and mobility of $CuGaTe_2$single crystal thin films deduced from Hall data are $8.72{\times}10{23}$개 $\textrm m^3$, $3.42{\times}10^{-2}$ $\textrm m^2$/V.s at 293K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the $CuGaTe_2$single crystal thin film, we have found that the values of spin orbit coupling $\Delta$s.o and the crystal field splitting $\Delta$cr were 0.0791 eV and 0.2463 eV at 10 K, respectively. From the PL spectra at 10 K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0470 eV and the dissipation energy of the donor-bound exciton and acceptor-bound exciton to be 0.0490 eV, 0.0558 eV, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.161-162
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• 2011

최근 광전자 분야에서는 미래 에너지 자원에 대한 관심과 함께 GaN 기반 태양전지 연구가 활발히 진행되고 있다. GaN 물질은 높은 전자 이동도와 높은 포화 속도 등 광전자 소자에 유리한 광, 전기적 특성들을 가지고 있다. 또한, In의 함량을 변화시켜가며, 0.7eV에서 3.4eV까지 밴드갭을 조절함으로써, 자외선부터 적외선까지 태양빛 스펙트럼의 대부분을 흡수할 수 있는 장점이 있다. InGaN 태양전지의 효율을 높이기 위해서는 In의 함량을 늘려 밴드갭을 줄이는 것이 중요하다. 하지만 GaN 와 InN 간의 격자 부정합으로 인해 In 함량이 높은 단결정 InGaN 층을 두껍게 성장 하는 것이 어렵다. 때문에 GaN 기반 태양전지 관련 연구 그룹들이 태양전지의 효율 향상을 위해 활성층에 양자우물(MQWs) 구조, Supper Lattice (SLs) 구조와 같이 얇은 InGaN/GaN 층을 주기적으로 반복하여 적층함으로써 높은 조성의 In을 함유한 상질의 InGaN/GaN 층을 성장하는 연구들을 진행해 왔다. 본 연구에서는, p-i-n 구조와 MQW 구조를 갖는 InGaN 기반 태양전지를 제작하여, 각각의 특성을 분석해 봄으로써, In0.1Ga0.9N 태양전지 활성층의 구조에 따른 장/단점에 대해 논의하였다. 먼저 MOCVD를 이용하여 200 nm의 i-In0.1Ga0.9N 활성층을 갖는 p-i-n 구조와 In0.19Ga0.81N/GaN(3 nm/8 nm) MQWs (8 periods) 구조를 갖는 태양전지 에피를 각각 성장하였고, 그 후 공정을 통해 그림 1과 같이 InGaN 태양전지 소자를 제작하였다. 그 후, 각 태양전지의 전류/전압 곡선과 외부양자효율을 측정하여 그림 2와 같은 결과를 얻었다. p-i-n과 MQW 샘플의 외부양자효율은 각각 ~70%, ~25%로 측정 되었다. MQW 샘플의 외부 양자효율이 높지 않음에도 불구하고 p-i-n 구조에 비해 높은 In 함량을 가지고 있으므로, 더 넓은 파장의 빛을 흡수하여, 높은 단락전류(0.778 mA/cm2)를 보이고 있다. 또한 p-i-n 구조에 비해 높은 개방전압(2.3V)를 가지고 있으므로, MQW 샘플이 약 17% 정도 높은 변환효율(1.4%)를 보이고 있다. 이후 추가적으로 p-i-n 과 MQW 구조의 InGaN 태양전지에 나타나는 Voc와 Jsc의 차이를 Polarization 효과를 비롯한 다양한 측면에서 분석해 보고자 한다.

• Korean Journal of Food Science and Technology
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• v.25 no.6
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• pp.775-779
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• 1993

The effects of water activity and light on the oxidation of carotenoid were studied using both the model systems of carrot lipids and freeze dried carrot. Autoxidation of crude lipids from the freeze dried carrot and the stability of carotenoids in controlled systems varing water activities and/or lights were examined. The degree of autoxidation of crude lipid stored at $30^{\circ}C$ for 16 days was significant(p< 0.05) and 71.8% destruction of carotenoid in the crude lipids were observed. When the powdered solid models of freeze dried carrot were stored at $30^{\circ}C$ for 35 days under various water activities and the presence of light, the maximum stability of carotenoid was found at $a_{w}$ 0.42 and the damaging effect of lights on the stability of carotenoid was significant (p<0.05). The absoprtion spectra of carotenoids changed according to the degree of oxidation, but shifts of the maximum wavelength was not observed.

• Resources Recycling
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• v.18 no.4
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• pp.24-30
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• 2009

Rare earth based calcium aluminate phosphor ($CaAl_2O_4:Eu^{2+}$, $Nd^{3+}$) supported $TiO_2$ nanoparticles are synthesized by using sol-gel method, which are further characterized using powder X-ray diffraction (XRD), fourier transform infrared (FT-IR), diffuse reflectance UV-Visible spectroscopy (DRS UV-Vis) and transmission electron microscopy (TEM). The XRD pattern of as-prepared and sintered phosphor supported $TiO_2$ does not show the tendency to change the crystal structure from anatase to rutile phase up to $600^{\circ}C$. This indicates that the phosphor support might inhibit the densification and crystallite growth by providing dissimilar boundaries. The diffuse reflectance spectral (DRS) measurements showed shift towards longer wavelength indicating reduction in the band-gap energy as compared to free $TiO_2$. The FT-IR spectra of phosphor supported $TiO_2$ nanoparticles show shift in the peak positions to lower wavelengths. This indicates that the $TiO_2$ nanoparticles are not free, but covalently bonded to the phosphor support. TEM micrographs show presence of crystalline and spherical $TiO_2$ nanoparticles (8 - 15 nm diameter) dispersed uniformly on the surface of phosphor.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.167-173
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• 2000

Four glasses of $B_2O_3-Bi_2O_3-PbO-SiO_2$ (BBPS) system were prepared by melting the appropriate amounts of reagent grade oxides of $B_2O_3$, $Bi_2O_3$, PbO, and $SiO_2$ in an open crucible. The differential thermal analysis showed crystallization temperature decreased with increasing $Bi_2O_3$ or PbO content in the sample. The structures of glasses system were studied using scanning electron microscopy and Fourier transform-Infra red (FT-IR) spectroscopy. The UV cut-off and refractive index were found to be sensitive to the $Pb^{+2}$ and $Bi^{+3}$ content in the glasses. The behavior of the IR spectra of the glasses in the BP series was consistent with a role of $Bi_2O_3$ as a network former. In the BP series of glasses, the result of IR spectrum indicated that PbO behaved as a network former.