• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.12
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• pp.1-7
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• 2001

Single-layer polymer green electroluminescent devices were fabricated with novel material synthesis by using moleculely-dispersed TTA and NIDI into the polymer PC(B79) emitter layer doped with C6 fluorescent dye which has low operating voltage and high quantum efficiency. A EL cell structure of glass substrate/indium-tin-oxide/PC:TTA:NIDI:C6/Ca/Al was employed and compared with various low work function cathode electrodes Ca and Mg metals. By adjusting the concentration of the fluorescent dye C6, low turn-on voltage of 2.4V was obtained, maximum quantum efficiency of 0.52% at 0.08mole% has been improved by about a factor of ~50 times in comparison with the undoped cell. The PL and EL colors can't be turned by changing the concentration of the C6 dopant. PL emission peaking was obtained at 495nm and EL emission peaking at 520nm with FWHM ~70nm

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.169-177
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• 2002

We develop the weighted-averaging finite-element method which uses four kinds of element sets. By constructing global stiffness and mass matrices for four kinds of element sets and then averaging them with weighting coefficients, we obtain a new global stiffness and mass matrix. With the optimal weighting coefficients minimizing grid dispersion and grid anisotropy, we can reduce the number of grid points required per wavelength to 4 for a $1\%$ upper limit of error. We confirm the accuracy of our weighted-averaging finite-element method through accuracy analyses for a homogeneous and a horizontal-layer model. By synthetic data example, we reconfirm that our method is more efficient for simulating a geological model than previous finite-element methods.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.430-435
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• 2011

$Y_{1-x}PO_4:{Eu_x}^{3+}$ red phosphors were synthesized with changing the concentration of $Eu^{3+}$ ion by using a solid-state reaction method. The crystal structures of all the red phosphors were found to be a tetragonal system composed of (200) diffraction peak centered at $25.88^{\circ}$, and the morphology of grains approached the spherical form with homeogenous size distribution as the concentration of $Eu^{3+}$ ion increased. As for the photoluminescence properties, all of the ceramic phosphors, irrespective of $Eu^{3+}$ ion concentration, showed the red-orange and the red emission peaked at 593.0 and 619.2 nm respectively. As the concentration of $Eu^{3+}$ ion increased, the excitation spectrum moved into a longer wavelength with the increase of emission intensity. The maximum excitation and the emission spectrum were observed at 0.15 mol of $Eu^{3+}$ ion.

• Journal of Applied Biological Chemistry
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• v.64 no.3
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• pp.217-223
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• 2021

5-aminolevulinic acid (ALA) is a representative photosensitizer used in numerous fields including cancer diagnosis and treatment. In this study, experiments were conducted to optimize the growth of Rhodobacter sphaeroides and production of ALA through LED irradiation of various wavelengths, addition of organic acid precursors of ALA, and changes in glucose concentration. After 72 h cultivation, the 850 nm wavelength LED irradiated at the same light intensity as the incandescent lamp increased the growth of R. sphaeroides and the production of ALA about 1.5- and 1.8-fold as compared with the control, respectively (p <0.0001 and p <0.0001). As a result of culturing R. sphaeroides by irradiating an LED with a wavelength of 850 nm after adding organic acid to the final concentration of 5 mM in culture medium, the production of ALA was increased about 2.8-fold in medium supplemented with pyruvic acid compared with the control (p <0.0001). In addition, the growth of the strain and the production of ALA were increased about 2.9- and 3.4-fold in medium supplemented with 40 mM glucose compared to the control which added only 5 mM pyruvic acid, respectively (p <0.0001 and p <0.0001). The yield of ALA per cell dry mass was about 1.4 folds higher than that of the control in 20 and 40 mM glucose, respectively (p <0.001). In conclusion, the growth of R. sphaeroides and production of ALA were increased by 850 nm wavelength LED irradiation. It also optimized the growth of R. sphaeroides and production of ALA through organic acid addition and glucose concentration changes.

• Applied Chemistry for Engineering
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• v.33 no.3
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• pp.309-314
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• 2022

Carbon dots (CDs) are few nanometer-sized carbon-based nanoparticles and emerging candidate materials in various fields such as biosensors and bioimaging due to their excellent optical properties and high biocompatibility. However, most CDs, emitting blue light, have limited their application in biomedical fields due to the low penetration of short-wavelength lights into the biological system. Therefore, there has been enormous need to develop long-wavelength emitting CDs. In this study, red-emitting CDs were successfully synthesized through the hydrothermal reaction of p-phenylenediamine with hydrochloric acid. In addition, the effect of the amount of hydrochloric acid on the formation of carbon dots, resulting in the variation of the chemical structures of CDs, were investigated, which was confirmed with the intensive structural analyses using infrared and X-ray photoelectron spectroscopy. It was found that the chemical structure of CDs governed their optical properties and quantum yield. Therefore, this study provides an insight into the role of acid in forming red-emitting CDs as the optimal probe for biomedical application.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.172-172
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• 2013

최근에 디스프로슘 이온이 도핑된 형광체의 백색 발광 현상 때문에 백색 발광 소재의 제조에 관한 연구가 상당한 관심을 끌고 있다. 본 연구에서는 $Eu^{3+}$와 $Dy^{3+}$ 이온의 몰 비를 변화시키면서 $BaNb_2O_6:RE^{3+}$ (RE=Eu, Dy) 형광체 분말을 합성한 결과를 보고한다. 특히 활성제 이온인 $Eu^{3+}$와 $Dy^{3+}$ 이온의 몰 비에 따른 $BaNb_2O_6$ 형광체 분말의 결정 구조, 입자의 모양과 크기, 흡광과 발광 스펙트럼의 변화를 관측하였고, 최적의 합성 조건을 제시하고자 한다. 파장 393 nm로 여기 시킨 $Dy^{3+}$ 이온의 몰 비에 따른 $BaNb_2O_6$ 형광체 분말의 발광 스펙트럼은 580 nm에 주 피크를 갖는 황색 스펙트럼이 관측되었다. 이 발광 신호는 $^4F_{9/2}-^6H_{13/2}$ 전이 신호이다. $Dy^{3+}$ 이온의 몰 비가 0 mol인 경우에는 발광 신호가 검출되지 않았다. $Dy^{3+}$ 이온의 몰 비가 0.10 mol일 때 발광 피크의 세기는 최대이었으며, $Dy^{3+}$ 이온의 몰 비가 더욱 증가함에 따라 발광 스펙트럼의 세기는 계속 증가하지 않고 갑자기 감소하기 시작하였다. 이것은 $Dy^{3+}$ 이온의 몰 비가 임계값을 초과하여 더욱 증가하면 모체 격자들 사이에 치환 고용되어 있는 $Dy^{3+}$ 이온들 사이의 거리가 더욱 가까워져서 $Dy^{3+}$ 이온들이 서로 용이하게 결합함으로써 내부 산란에 의하여 발광의 세기가 감소함을 의미한다. 흡광 스펙트럼의 경우에, $Dy^{3+}$ 이온의 몰 비가 0.01 mol일때 형광체 분말은 두 종류의 흡광 스펙트럼을 나타내었다. 첫째는 $Dy^{3+}$ 양이온과 $O^{2-}$ 음이온들 사이에 발생한 전하 전달 밴드에 의해 발생하는 310 nm를 정점으로 하여 280~340 nm 영역에 걸쳐서 광범위하게 분포하는 흡광 신호가 관측되었으며, 둘째는 $Dy^{3+}$ 이온의 $4f^9$ 전자 배열 내에서 발생하는 4f-4f 전이 신호로서, 이것은 350~500 nm 영역에 걸쳐서 비교적 밴드폭이 좁은 다수의 흡광 신호가 나타났다. 본 실험에서는 다섯 개의 피크를 갖는 흡광 신호가 검출되었는데, 이중에서 제일 강한 주 피크인 393 nm의 흡수 파장은 모체 격자 내에 있는 $Dy^{3+}$ 이온의 바닥 상태인 $^6H_{15/2}$ 준위에서 여기 상태인 $^4F_{7/2}$ 인 에너지 준위로 전이하면서 발생한 신호이며, 이에 비하여 상대적으로 흡광 세기가 약한 370, 432, 458, 370 nm의 흡수 파장이 관측되었다.

• Applied Chemistry for Engineering
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• v.21 no.6
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• pp.638-642
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• 2010

After phthalonitrile derivatives were synthesized by the introduction of phenoxy, 2-naphthoxy or 4-trityl phenoxy group on ${\alpha}$- and ${\beta}$-position, oxovanadyl phthalocyanine (VOPc) derivatives containing electron-rich substituent group at different position were synthesized successfully in this investigation. The chemical structure of samples was determined by the means of $^1H$-NMR, MALDI-TOF mass spectroscopy, and FT-IR spectrometer. Also, optical and chemical properties were determined by the means of UV-Vis spectrometer, X-ray diffractometry, and thermo gravimetry. It was found that the maximum absorbing wavelength of VOPc derivatives ranged from 684 to 726 nm. Also, their solubility and Q-band were enhanced and shifted by the introduction of substitute group, respectively.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.503-515
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• 2012

${\alpha},{\beta}$-Dichlorosuccinic acid was synthesized through the reaction of maleic anhydride with $Cl_2$(g) and ultra violet(200~300nm) wavelength in the presence of $CCl_4$. The second reaction of N-(${\alpha},{\beta}$-dichloro)succinic acid contained glucosamine derivatives(I) was accomplished by a modification of the general acylation using excess ${\alpha},{\beta}$-dichlorosuccinic anhydride in the presence of 2% acetic acid with methanol as a solvent at elevated temperature($70^{\circ}C$). We considered organic acid derivatives were useful especially of treatment for the cultivating porphyra and skin beauty culture.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.26.2-26.2
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• 2011

최근 주목 받고 있는 산화아연(ZnO)은 레이저 다이오드, 가스 센서, 자외선 센서, 투명전극 등으로 다양하게 사용될 수 있어 연구개발이 폭 넓게 이루어지고 있는 상황이다. 특히, 3.3 eV의 direct bandgap 에너지를 가지고 있는 ZnO은 현재 자외선센서로 많이 적용되고 있는 물질인 GaN계열을 대체할 수 있는 유망한 물질로 주목 받고 있다. 공기중의 산소나 수분의 표면반응에 의한 자외선 측정을 하는 ZnO을 나노선으로 만들게 되면, 표면대비 부피비가 박막에 비해 급격히 증가하기 때문에 민감도가 커지고 반응시간이 짧아지게 된다. 본 연구에서는 자외선센서의 민감도와 반응성을 향상시키기 위해 전기화학적 합성법을 통해 ZnO의 박막과 나노선을 제조하였다. 사진공정을 통해 3 ${\mu}m$의 간격을 가진 금(Au) 전극을 만든 후, 전기화학적 합성법을 통해 아연이온이 포함된 용액에서 정전류를 흘려보내 아연 또는 ZnO을 증착시킬 수 있었다. 첫 번째로 ZnO을 양쪽 Au 전극에서 동시에 증착하여 두 박막이 접합하였고, 두 번째는 100nm의 지름을 가진 Ni 나노선를 전극 양쪽에서 자석을 통해 자기장을 형성해 정렬시키고 ZnO을 Au 전극과 Ni 나노선에 증착한 후, Ni 나노선를 산화시킴으로써, ZnO 나노구조를 형성하였다. 세 번째로는 Au 전극 양쪽에 아연을 전기화학적 합성을 하여 박막으로 증착하고 고온에서 산화과정을 통해 100 nm 이하의 지름을 가진 ZnO 나노선를 형성하였다. 이렇게 만들어진 세가지 구조의 ZnO의 나노구조와 결정성은 주사전자현미경과 X선 회절 분석기를 통해 측정하였으며, 자외선에 대한 민감도와 반응성은 365 nm의 파장을 가진 자외선발생기와 소스미터장치를 통해 측정하였다. 박막에서 100 nm 이하의 지름을 가진 ZnO 나노선로 갈 수록 자외선에 대한 민감도와 반응성이 향상되었다.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.694-697
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• 2019

In recent years, titanium dioxide powders were produced as nanoparticles or nanowires or nanotubes in one-dimensional structure, and mesoporous spheres in 3-D to improve their crystallinities, which were further used as photo-electrode materials and for preventing photo-aging. In this study, a nano sol composed of titanium dioxide exhibiting a high crystallinity was synthesized using n-alcohol as a solvent. The crystallinity of the nano sol was confirmed by FE-SEM, and XRD, while the UV blocking rate confirmed by UV-Vis spectrometry results. Changes in the crystallinity were investigated by varying the types of solvents such as butanol, propanol and ethanol. The synthesized particle sizes were from 200 to 250 nm, and the optical transmittance showed a high blocking rate in the UVB and UVA range. It is expected that a high transmittance at 550 nm wavelength can increase the photoelectric conversion efficiency of solar cells and the UV blocking efficiency.