• Journal of the Korean Society for Precision Engineering
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• v.26 no.1
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• pp.51-56
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• 2009

Recently, with the increasing lightness and miniaturization of high resolution camera phones, the demand for aspheric glass lens has increased because plastic and spherical lens are unable to satisfy the required performance. An aspheric glass lens is fabricated by the high temperature and pressure molding using a tungsten carbide molding core, so precision grinding and coating technology for the molding core surface are required. This study investigates the effect of diamond-like carbon (DLC) and rhenium-iridium (Re-Ir) coating For aspheric molding core surface. The grinding conditions of the tungsten carbide molding core were obtained by design of experiments (DOE) for application in the ultra precision grinding process of the tungsten carbide molding core of the aspheric glass lens used in 5 megapixel, $4{\times}$ zoom camera phone modules. A tungsten carbide molding core was fabricated under this grinding condition and coated with the DLC and Re-Ir coating. By measurements, the effect of DLC and Re-Ir coating on the form accuracy and surface roughness of molding coer was evaluated.

• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3590-3594
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• 2014

Blue phosphorescent $(dfpypy)_2Ir(mppy)$, where dfpypy = 2',6'-difluoro-2,3'-bipyridine and mppy = 5-methyl-2-phenylpyridine, has been synthesized by newly developed effective method and its solid state structure and photoluminescent properties are investigated. The glass-transition and decomposition temperature of the compound appear at $160^{\circ}C$ and $360^{\circ}C$, respectively. In a crystal packing structure, there are two kinds of intermolecular interactions such as hydrogen bonding ($C-H{\cdots}F$) and edge-to-face $C-H{\cdots}{\pi}(py)$ interaction. This compound emits bright blue phosphorescence with ${\lambda}_{max}=472nm$ and quantum efficiencies of 0.23 and 0.32 in fluid and the solid state. The emission band of the compound is red-shifted by 40 nm relative to homoleptic congener, $Ir(dfpypy)_3$. The ancillary ligand in $(dfpypy)_2Ir(mppy)$ has been found to significantly destabilize HOMO energy, compared to $Ir(dfpypy)_3$, $(dfpypy)_2Ir(acac)$ and $(dfpypy)_2Ir(dpm)$, without significantly changing LUMO energy.

• Journal of the Semiconductor & Display Technology
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• v.8 no.4
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• pp.15-19
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• 2009

A high efficient organic red light emitting device with structure of DNTPD/TAPC/$Bebq_2$ :[$(pq)_2Ir(acac)$, SFC-411]/SFC-137 was fabricated on the plastic substrate, which can be applied in the fields of flexible display and illumination. In the device structure, N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolylamino)-phenyl]-biphenyl-4,4'-diamine[DNTPD] as a hole injection layer and 1,1-bis-(di-4-tolylaminophenyl) cyclohexane [TAPC] as a hole transport were used. Bis(10-hydroxybenzo[h]quinolinato) beryllium complex [$Bebq_2$] was used as a light emitting host material. The host material, $Bebq_2$ was doubly doped with volume ratio of 7% iridium(III)bis-(2-phenylquinoline)acetylacetonate[$(pq)_2$Ir(acac)] and 3% SFC-411[red phosphor dye coded by the proprietary company]. And then, SFC-137 was used as an electron transport layer. The luminous intensity and current efficiency of the fabricated device were $22,780\;cd/m^2$ at 9V and 17.3 cd/A under $10,000\;cd/m^2$, respectively. The maximum current efficiency of the device was 22.4cd/A under $580\;cd/m^2$.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.795-800
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• 2002

Yb:$YCa_4O(BO_3)_3$ (Yb:YCOB) single crystal, in which the concentration of $Yb^{3+}$ ion 20 at%, was grown by the Czocharalski method using an iridium crucible under N2 atmosphere. The optimum growth parameters to get a high quality of single crystals were found to be 1.5∼2 mm/h of pulling rate and 10∼20 rpm of rotation rate. According to the results of spectroscopic properties, absorption edge of Yb:YCOB was 236 nm. Two strong absorption line due to $Yb^{3+}$ ions were observed at 900 and 975 nm. Thermal expansion coefficients of Yb:YCOB crystal along a, b and c crystallographic axes from 320 to 650 K were 12.1${\times}10^{-6}$/K, 5.9${\times}10^{-6}$/K, 12.9${\times}10^{-6}$/K, respectively. Specific heat was 0.162 $cal/g{\cdot}K$ at 330 K.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.272-273
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• 2011

유기발광소자는 차세대 디스플레이 소자로서 빠른 응답 속도, 높은 색 재현성 및 매우 얇은 두께로 제작이 가능한 장점을 가지고 있어서 차세대 디스플레이 소자로서 많은 응용 가능성을 가지고 있다. 청색 유기발광소자는 적색 및 녹색의 유기발광소자의 발광 효율 특성보다 상대적으로 효율이 떨어지고, 색 순도가 낮으며 수명이 짧은 단점을 가지고 있어 소자 특성을 개선해야 한다. 본 논문에서는 청색 유기발광소자의 색 순도와 색 안정성 증진을 위하여 발광층을 2개의 층으로 나누어 15 nm 두께의 4,4'-Bis(2,2-diphenyl-ethen-1-yl)diphenyl (DPVBi) 형광 청색 호스트 물질에 4,4 '-Bis[4-(diphenylamino)stylyl]biphenyl (BDAVBi) 형광 청색 게스트 물질을 첨가하여 제 1 형광 발광층을 형성하고 15 nm 두께의 4,4'-Bis(carbazol-9-yl)biphenyl (CBP) 인광 호스트 물질에 bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium III (FIrpic) 인광 게스트 물질을 첨가한 제 2 인광 발광층으로 구성된 30 nm 두께의 하이브리드 발광층을 사용하여 청색 유기 발광소자를 제작하고 전기적 특성과 광학적 성질을 조사하였다. 하이브리드 발광층을 사용하여 제작된 유기발광소자는 20 mA/cm2의 전류 밀도에서 6.2 cd/A의 발광 효율을 나타내었고, 최대 밝기는 약 16,200 cd/m2로 측정 되었다. 하이브리드 발광층을 사용한 청색 유기발광소자는 전류의 흐름이 단일 발광층 유기발광소자에 비교하여 상대적으로 안정적인 전류 흐름을 가지며 발광층 내부에 더 많은 정공과 전자를 포획하여 엑시톤 형성 확률이 증가하여 발광효율과 밝기가 향상되었다. 하이브리드 발광층을 적용한 유기발광소자는 469 nm파장에서 형광 발광층의 주 전계발광 피크가 나타났고 그와 함께 인광 발광층의 부 전계발광 피크가 491 nm의 파장에서 관측되었다. 또한 전계발광 스펙트럼의 반치폭이 10 nm 감소하여 청색의 색 순도 증가에도 기여하였다. 하이브리드 발광층을 가진 청색 유기발광소자의 색 좌표는 전압 변화에 관계없이 일정한 값을 나타내었다. 이러한 결과는 형광과 인광 발광층으로 구성된 하이브리드 발광층 유기발광소자가 전기적으로 안정성을 가지며 발광 특성을 개선하고 안정적인 청색 유기 발광 디스플레이 소자로 사용 가능함을 나타내고 있다.

• Journal of Radiation Protection and Research
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• v.35 no.1
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• pp.26-33
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• 2010

A computed Radiography (CR) system by use of reusable Image Plate (IP) offers a convenient and reliable way to replace a conventional film-screen system for NDT (non-destructive testing) field. The quality of a radiography to detect a defect of welded objects depends on the procedure embracing several factors such as measurement conditions, image plate type/class, radiation energy, radiation type, and source to image plate distance. Also, the ability of images to detect a flaw reduces with increasing object thickness. In the study, the properties of gamma ray source were summarized for NDT field and inspection images of CR image system manufactured by FUJI were acquired using $^{75}Se$ and $^{192}Ir$ with welded objects. We analyzed the gray scale of hole defect image by using XCAP image processing program and calculated the image contrast and SNR in definition. Also the sesitivities of image quality indicator(IQI) were calculated for hot and cooling tube image of $^{75}Se$ and $^{192}Ir$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.5
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• pp.504-515
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• 1997

In this paper, interference of non-GSO/MSS system into M/W radio stations has been analyzed as two aspects. One is that PDF(Power Flux Density) levels, which are received by M/W radio stations from non-GSO satellites, were simulated and compared with the threshold level specified in ITU-R SF.357. The other is that C/I values, which have been utilized in estimating interference between conventional fixed services, were simulated and analyzed by means of calculating excess time percent and duration below the C/I protection ratio. As the results, it was shown that interference levels received by M/W stations from non- GSO/MSS satellites don't exceed above the threshold level at all, even if changing parameters related with M/W stations. In addition, the excess percent time below the interference protection ratio is a long term of 32% in the case of Iridium interfering into a M/W stations route, but only a short term of 1.71% in the case of Globalstar interfering into a M/W stations route.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.240-244
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• 2009

Simple and high efficiency green phosphorescent devices using an intermixed double host of 4, 4', 4"-tris(N-carbazolyl) triphenylamine [TCTA], 1, 3, 5-tris (N-phenylbenzimiazole-2-yl) benzene [TPBI], phosphorescent dye of tris(2-phenylpyridine)iridium(III) [$Ir(ppy)_3$], and selective doping in the TPBI region were fabricated, and their electro luminescent characteristics were evaluated. In the device fabrication, layers of $70{\AA}$-TCTA/$90{\AA}$-$TCTA_[0.5}TPBI_{0.5}$/$90{\AA}$-TPBI doped with $Ir(ppy)_3$ of 8% and an undoped layer of $50{\AA}$-TPBI were successively deposited to form an emission region, and SFC137 [proprietary electron transporting material] with three different thicknesses of $300{\AA}$, $500{\AA}$, and $700{\AA}$ were used as an electron transport layer. The device with $500{\AA}$-SFC137 showed the luminance of $48,300\;cd/m^2$ at an applied voltage of 10 V, and a maximum current efficiency of 57 cd/A under a luminance of $230\;cd/m^2$. The peak wavelength in the electroluminescent spectral and color coordinates on the Commission Internationale de I'Eclairage [CIE] chart were 512 nm and (0.31, 0.62), respectively.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2955-2960
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• 2010

Spiro-type orange phosphorescent host materials, 9-diphenylphosphine oxide-spiro[fluorene-7,9'-benzofluorene] (OPH-1P) and 5-diphenylphosphine oxide-spiro[fluorene-7,9'-benzofluorene] (OPH-2P) were successfully prepared by a lithiation reaction followed by a phosphination reaction with diphenylphosphinic chloride. The EL characteristics of OPH-1P and OPH-2P as orange host materials doped with iridium(III) bis(2-phenylquinoline)acetylacetonate ($Ir(pq)_2acac$) were evaluated. The electroluminescence spectra of the ITO (150 nm)/DNTPD (60 nm)/NPB (30 nm)/OPH-1P or OPH-2P: $Ir(pq)_2acac$ (30 nm)/BCP (5 nm)/$Alq_3$ (20 nm)/LiF (1 nm)/Al (200 nm) devices show a narrow emission band with a full width at half maximum of 75 nm and $\lambda_{max}$ = 596 nm. The device obtained from OPH-1P doped with 3% $Ir(pq)_2acac$ showed an orange color purity of (0.580, 0.385) and an efficiency of (14 cd/A at 7.0 V). The ability of the OPH-P series to combine a high triple energy with a low operating voltage is attributed to the inductive effect of the P=O moieties and subsequent energy lowering of the LUMO, resulting in the enhancement of both the electron injection and transport in the device. The overall result is a device with an EQE > 8% at high brightness, but operating voltage of less than 6.4 V, as compared to the literature voltages of ~10 V.

• Journal of Hydrogen and New Energy
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• v.29 no.3
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• pp.260-266
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• 2018

To enhance catalyst activity of the palladium (Pd) towards oxygen reduction reaction (ORR), iridium (Ir) and yttrium (Y) were alloyed by polyol method. Due to the low reduction potential of Y, it is hard to reduce Y ion completely by polyol method. In XPS spectra, the binding energy of the Pd is shifted to a lower value, which indicates the d-electron of Pd is filled by the electron from the Y. And other phases of Y are observed by the XPS. Among the catalysts, the $Pd_4IrY_{0.1}/C$ showed the best activity towards ORR, which indicates the metallic Y is effective for improving the catalytic activity. Thus, for further enhancing ORR activity, the novel method for complete reduction of Y is needed.