• Journal of Information Display
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• v.9 no.3
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• pp.23-27
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• 2008

This paper reports that well-balanced white emission with three primary colors can be achieved with a simple white organic light-emitting diode (WOLED) structure of ITO / $\alpha$-NPD (50 nm) / $\alpha$-NPD: Btp2Ir(acac) (8 wt%, 6 nm) / $\alpha$-NPD (5 nm) / BCP (3 nm) / $Alq_3$: C545T (0.5 wt%, 10 nm) / $Alq_3$ (40 nm) / LiF (0.5 nm) / Al (100 nm). The external quantum efficiency of the device reached 3.8% at a current density (luminance) of 4.6 mA/$cm^2$ (310 cd/$m^2$), and the maximal luminance of the device reached 19,000 cd/$m^2$ at 11.5 V. The insignificant blue shift of the emitting color with an increasing current density can be attributed to the narrowing of the exciton formation zone width.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.221-221
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• 2016

최근에 희토류 이온이 도핑된 텅스텐산(tungstates) 형광체에 대한 연구가 재조명되고 있다. 텅스텐산 형광체는 우수한 광학적 특성과 높은 화학적 안정성을 나타내기 때문에 X-선 증강 스크린(X-ray intensifying screens), 광고판용 형광 램프, 발광 다이오드, 레이저, 섬광체(scintillator), 전계방출 디스플레이 영역에 그 응용성을 넓히고 있다. 본 연구는 모체 결정 MgWO4에 희토류 이온인 Tb3+와 융제(flux)의 몰 비를 변화 시켜 고상반응법을 사용하여 합성을 하였다. 합성한 형광체를 여기 파장 281 nm로 제어하였을 시, 545 nm의 녹색 발광 스펙트럼을 관찰 하였다. Tb3+이온이 0.10 mol일 때, 가장 발광 세기가 컸으며, 몰비가 증가 할수록 발광의 세기는 점차 커지다가 0.12 mol에서 작아졌다. 주 발광 신호 이외에도 489 nm, 586 nm, 621 nm에서 상대적으로 작은 발광 스펙트럼을 보였다. XRD를 통해 분석한 결정구조는 단사정계임을 알 수 있었으며 주 피크는 $23.9^{\circ}$에서 발생 하였고 이는 (110)면에서 발생한 회절 신호이다.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.143-148
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• 2013

Well-distributed $SnO_2$-Sn-$Ag_3Sn$ nanoparticles embedded in carbon nanofibers were fabricated using a co-electrospinning method, which is set up with two coaxial capillaries. Their formation mechanisms were successfully demonstrated. The structural, morphological, and chemical compositional properties were investigated by field-emission scanning electron spectroscopy (FESEM), bright-field transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In particular, to obtain well-distributed $SnO_2$ and Sn and $Ag_3Sn$ nanoparticles in carbon nanofibers, the relative molar ratios of the Ag precursor to the Sn precursor including 7 wt% polyacrylonitrile (PAN) were controlled at 0.1, 0.2, and 0.3. The FESEM, bright-field TEM, XRD, and XPS results show that the nanoparticles consisting of $SnO_2$-Sn-$Ag_3Sn$ phases were in the range of ~4 nm-6 nm for sample A, ~5 nm-15 nm for sample B, ~9 nm-22 nm for sample C. In particular, for sample A, the nanoparticles were uniformly grown in the carbon nanofibers. Furthermore, when the amount of the Ag precursor and the Sn precursor was increased, the inorganic nanofibers consisting of the $SnO_2$-Sn-$Ag_3Sn$ nanoparticles were formed due to the decreased amount of the carbon nanofibers. Thus, well-distributed nanoparticles embedded in the carbon nanofibers were successfully synthesized at the optimum molar ratio (0.1) of the Ag precursor to the Sn precursor after calcination of $800^{\circ}C$.

• Journal of the Korea Institute of Building Construction
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• v.23 no.2
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• pp.113-121
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• 2023

In this study, the applicability and reproducibility of laser induced breakdown spectroscopy(LIBS) for heavy metal analysis in clinker and 5 types of by-products(crushed stone sludge, blast furnace slag, steel slag, waste concrete sludge, bottom ash) were experimentally reviewed. As a result of ICP-MS, XRF, and LIBS analysis of the six samples, the difference between ICP and XRF was confirmed in the quantitative analysis, but the LIBS analysis showed a difference by element from the standard analysis, and only qualitative analysis of the sample was possible. LIBS analysis wavelength was set for three types of heavy metals(Cd - 214.44nm, Pb - 405.78nm, Hg - 253.65nm). As a result of laser irradiation on the surface of the membrane impregnated with a solution of each concentration(1~1000ppm) and dried, the correlation between the spectral intensity and the concentration was confirmed.

• Korean Journal of Agricultural and Forest Meteorology
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• v.23 no.1
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• pp.15-33
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• 2021

In this study, the possibility of discriminating Fire blight (FB) infection tested using the hyperspectral imagery. The reflectance of healthy and infected leaves and branches was acquired with 5 nm of full width at high maximum (FWHM) and then it was standardized to 10 nm, 25 nm, 50 nm, and 80 nm of FWHM. The standardized samples were divided into training and test sets at ratios of 7:3, 5:5 and 3:7 to find the optimal bands of FWHM by the decision tree analysis. Classification accuracy was evaluated using overall accuracy (OA) and kappa coefficient (KC). The hyperspectral reflectance of infected leaves and branches was significantly lower than those of healthy green, red-edge (RE) and near infrared (NIR) regions. The bands selected for the first node were generally 750 and 800 nm; these were used to identify the infection of leaves and branches, respectively. The accuracy of the classifier was higher in the 7:3 ratio. Four bands with 50 nm of FWHM (450, 650, 750, and 950 nm) might be reasonable because the difference in the recalculated accuracy between 8 bands with 10 nm of FWHM (440, 580, 640, 660, 680, 710, 730, and 740 nm) and 4 bands was only 1.8% for OA and 4.1% for KC, respectively. Finally, adding two bands (550 nm and 800 nm with 25 nm of FWHM) in four bands with 50 nm of FWHM have been proposed to improve the usability of multispectral image sensors with performing various roles in agriculture as well as detecting FB with other combinations of spectral bands.

• Journal of Internet Computing and Services
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• v.10 no.1
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• pp.1-9
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• 2009

In this paper, A pipeline structured-degree computationless modified Euclidean (PS-DCME) algorithm is proposed, which can be used for a RS(23,17) decoder for MB-OFDM system. PS-DCME algorithm requires a state machine instead of the degree computation and comparison circuits, so that the hardware complexity of the decoder can be reduced and high-speed decoder can be implemented. We have implemented a RS(23,17) decoder with PS-DCME using Verilog HDL and synthesized with Samsung 65nm library. From synthesis results, it can operate at clock frequency of 250MHz, and gate count is 19,827.

• Journal of Biosystems Engineering
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• v.36 no.1
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• pp.23-32
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• 2011

In this work, the finite element method was used to investigate the shifts of resonance frequencies and quality factor of whispering-gallery-mode (WGM) for an opto-fluidic ring resonator (OFRR) biosensor. To describe the near-field radiation transfer, the time-domain Maxwell's equations were employed and solved by using the in-plane TE wave application mode of the COMSOL Multiphysics with RF module. The OFRR biosensor model under current study includes a glass capillary with a diameter of 100 mm and wall thickness of 3.0 mm. The resonance energy spectrum curves in the wavelength range from 1545 nm to 1560 nm were examined under different biosensing conditions. We mainly studied the sensitivity of resonance shifts affected by changes in the effective thickness of the sensor resonator ring with a 3.0 mm thick wall, as well as changes in the refractive index (RI) of the medium inside ring resonators with both 2.5 mm and 3.0 mm thick walls. In the bulk RI detection, a sensitivity of 23.1 nm/refractive index units (RIU) is achieved for a 2.5 mm thick ring. In small molecule detection, a sensitivity of 26.4 pm/nm is achieved with a maximum Q-factor of $6.3{\times}10^3$. These results compare favorably with those obtained by other researchers.

• Proceedings of the Korean Society of Crop Science Conference
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• 2022.10a
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• pp.108-108
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• 2022

In this study, multispectral images of wheat according to soil water state were collected, compared, and analyzed to measure the physiological response of crops to environmental stress at the individual level. CMS-V multi-spectral camera(Silios Technologies) was used for image acquisition. The camera lens consists of eight spectral bands between 550nm and 830nm. Light Reflective information collected in each band sensor and stored in digital values, and it is converted into a reflectance for calculating the vegetation index and used. According to the camera manual, the NDVI(Normalized Difference vegetation index) value was calculated using 628 nm and 752 nm bands. Image measurement was conducted under natural light conditions, and reflectance standards(Labsphere) were captured with plants for reflectance calculation. The wheat variety used Gosomil, and the wheat grown in the field was transplanted into a pot after heading date and measured. Three treatments were performed so that the soil volumetric water content of the pot was 13~17%, 20~23%, and 25%, and the growth response of wheat according to each treatment was compared using the NDVI value. In the first measurement after port transplantation, the difference in NDVI value according to treatment was not significant, but in the subsequent measurement, the NDVI value of the treatment with a water content of 13 to 17% was lowest and was the highest at 20 to 23%. The NDVI values decreased compared to the first measurement in all treatment, and the decrease was the largest at 13-17% water content and the smallest at 20-23%. Although the difference in NDVI values could be confirmed, it would be difficult to directly relate it to the water stress of plants, and further research on the response of crops to environmental stress and the analysis of multi-spectral image will be needed.

• Journal of the Korean institute of surface engineering
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• v.49 no.3
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• pp.316-321
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• 2016

To study emission characteristics for dual-emission tandem organic light emitting display (OLED), we fabricated blue fluorescent OLED according to thickness variation of $MoO_x$ as charge generation layer and Al as cathode. The bottom emission characteristics of OLED with $MoO_x$ 2, 3, 5 nm thickness showed threshold voltage of 9, 7, 9 V, maximum current emission efficiency of 19.32, 23.18, 15.44 cd/A and luminance of $1,000cd/m^2$ at applied voltage of 17.6, 13.2, 16.5 V, respectively. The top emission characteristics of OLED with $MoO_x$ 2, 3, 5 nm thickness indicated threshold voltage of 13, 10, 13 V, maximum current emission efficiency of 0.17, 0.23, 0.16 cd/A and luminance of $50cd/m^2$ at applied voltage of 22.6, 16.5, 20.1 V, respectively. In case of thicker or thinner than $MoO_x$ of 3 nm, the emission characteristics were decreased because of mismatching of electron and hole in emission layer. The bottom emission characteristics of OLED with Al 15, 20, 25 nm thickness showed threshold voltage of 8, 8, 7 V, maximum current emission efficiency of 18.42, 22.98, 23.18 cd/A and luminance of $1000cd/m^2$ at applied voltage of 16.2, 13.9, 13.2 V, respectively. The reduction of threshold voltage and increase of maximum current emission efficiency are caused by the increase of current injection according to increase of Al cathode thickness. The top emission characteristics of OLED with Al 15, 20, 25 nm thickness indicated threshold voltage of 7, 7, 8 V, maximum emission luminance of 371, 211, $170cd/m^2$, respectively. The top emission OLED of Al cathode with 15 nm thickness showed maximum luminance and it decreased at thickness of 20 nm. These phenomena are caused by the decrease of intensity of emitted light by reduction of optical transmittance according to increase of Al cathode thickness.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.4
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• pp.23-30
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• 2001

In this paper, the discharge image of NO particles wire-cylinder type electrode in the discharge reactor where AC dielectric barrier type corona discharge occurred and horizontal and vertical signal intensity at each flourescence emission during discharge and the horizontal and vertical signal strength of NO particles at flourescence emission wavelength band[236[nm], 247[nm]], were measured were measured by ICCD Camera. In addition discharge images and signal intensities in accordance with discharge time were measured to figure out the discharge mechanism. It was found that the strongest horizontal and vertical signal intensity of NO particles were observed at 247[nm] band, but no big difference in the horizontal and vertical signal intensity in accordance with discharge time was seen. In particular, the phenomenon image occuring inside the discharge reactor and wavelength ware able to be carried based on the measured data.