• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1999.06a
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• pp.69-76
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• 1999

This paper proposes a new region-oriented coding scheme of still images. The scheme first segments an image into homogeneous regions by making use of Voronoi diagrams. Then luminance components in each Voronoi region are encoded using a transform coding technique which employs the Schmidt's orthogonalization method to produce orthonormal basis-functions for arbitrarily shaped regions. In this technique, coding efficiency depends on the properties of initial vectors to be orthogonalized. Therefore we adaptively select a set of initial vectors as well as the order in which these vectors are orthogonalized. Simulation results indicate that the proposed coding scheme achieves higher coding performance with much less computation than the KLT-based scheme which we reported formerly.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.103-107
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• 2006

In this paper, the dimmable electronic ballast for the 250W metal halide lamp was realized by three stage structure. We developed stable the dimming ballast by using a Micro-controller, and measured the output wattage in the dimming range(illumination) from 100% to about 20%. Under the 35% dimming level, it is possible to cause the redution of lamp's life. The dimming performance can reduce the light system's wattage but can reduce the luminance efficiency (lux/watt).

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.40-42
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• 2002

본 논문은 AC PDP의 유지방전 구간에서 전하 제어를 통하여 저전압 구동과 고발광효율을 구현하기위한 새로운 구동 방식을 소개하고, 이 구동방식에 대한 실험결과 및 특성을 소개한다. 이 방식은 패널에 전원을 직접 인가하는 대신 외부 저장 커패시터에 연결하며 여기에 충전된 전압을 LC 공진을 통하여 중간 저장 커패시터를 충전하고 이 중간커패시터에 충전된 제한된 전하로 패널을 간접적으로 구동하는 방식으로, 기존의 방법보다 패널을 방전시키기 위한 전원의 공급 전압을 절반으로 낮출 수 있으며, 패널에 방전 시 공급되는 전력을 제한함으로서 발광효율을 개선할 수 있다. 전하 제어 구동 방식을 4인치 패널에 적용하여 실험한 결과 107V의 낮은 전압의 전원으로 안정된 방전을 유지할 수 있었으며, 1.28 lm/W의 높은 발광효율을 얻을 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.510-511
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• 2005

Several iridium based complexes were investigated as blue phosphorescent dopants. They are achieved about 100 % quantum efficiencies due to utilization of both singlet and triplet excitons in the radiative processes. We have fabricated phosphorescent OLED with 8 % Ir$(ppz)_3$ as a triplet emissive dopnat in diverse host materials. In this study, the CBP obtained the luminance efficiency of 0.20 cd/A adapts to the host material. Furthermore, we synthesize metalorganic phosphor complexs based on Ir heavy metal with different ligands as to $Ir(ppz)_2acac$, $(Im)_2Ir(acac)$, $(Im-R)_2Ir(acac)$.

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.98-103
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• 2001

A new application of dirchroic mirror for the improvement of luminance and luminous efficacy in an AC-Plasma Display Panel (PDP) is suggested. Only about half of the Vacuum Ultraviolet (VUV) generated in the reflective PDP cell is used for the excitation of the phosphor. We are suggesting an idea of adopting a dichroic mirror which can reflect the VUV toward the phosphor which otherwise is absorbed by the front panel. The optical constants of the thin films of dirhroic mirror were determined from the photometric measurements through an iteration process of matching calculated and measured values of the reflectance and transmittance in the VUV wavelength region. From these results, we could design such a filter whose high reflection zone is centered at 147nm by a computer simulation accurately. The 147nm VUV is radiated from Xenon 3Pl state which is dominantly used to activate the phosphor in the PDP cell. The dichroic mirror was made with an electronbeam evaporator and its reflectance was measured by a reflectometer. We confirmed the usefulness of the dichroic mirror for the improvement of efficiency with experiments done by test panels. The panel with mirror shows improved luminance and luminous efficacy by 20∼30％.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.155-159
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• 2005

In this report, Polymer light emitting diodes (PLEDs) with an ITO/PEDOT:PSS/MEH-PPV/Al structure were prepared by spin coating method on the glass substrate patterned ITO (indium tin oxide), using PEDOT:PSS(poly(3,4=ethylenedioxythiophene):poly(styrene sulfolnate)) as the hole transfer material and MEH-PPV(poly(2-methoxy-5-(2-ethyhexoxy)-1,4-phenylenvinylene)) having a different concentration (0.1, 0.3, 0.5, 0.7, 0.9, 1.5 wt$\%$) as the emitting material. The electrical and optical properties of the prepared PLED samples were investigated. The good electrical and optical properties were observed for the PLED samples with a MEH-PPV concentration ranging from 0.5 to $0.9 wt\%$. However, the current and luminance values for PLED sample with $1.5 wt\%$ of MEH-PPV decreased greatly. The maximum luminance and light efficiency for the PLEDs with concentration of $0.5 wt\%$ MEH-PPV were $409 cd/m^2$ and 4.90 Im/W at 9 V, respectively. The emission spectrums were found to be $560{\~}585 nm$ in wavelength showing orange color.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.50-55
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• 2014

It was firstly found in 1st group element. Recently, it has been reported on the improvement of efficiency of the OLEDs by introducing thin layer of some carbonate materials of alkali metal. In order to improve the efficiency of OLEDs which is one of the next generation displays, we have studied the electrical characteristics of the device depending on the thickness ratio of the hole-injection layer to the electron-injection layer. Teflon-AF was used as the hole-injection material, and alkali-metal carbonates of $Li_2CO_3$ were used as the electron-injection materials. To obtain a proper thickness ratio, we manufactured. Four types of devices with the thickness ratio of HIL to EIL were made to be 1 : 4, 2 : 3, 3 : 2, and 4 : 1. The results of electrical and optical properties showed that the device with the thickness ratio of 4 : 1 is the most excellent result. In addition, to prepare a four-layer device by inserting the ${\alpha}$-NPD is a hole transporting material was compared with three-layer element. As a result, the maximum luminance, the maximum luminous efficiency, maximum external quantum efficiency of about 124 [%], 164 [%], 106 [%] improve was confirmed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.5
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• pp.344-349
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• 2015

A new information society of late has arrived by the rapid development of various information & communications technologies. Accordingly, mobile devices which are light and thin, easy and convenient to carry on the market. Also, the requirements for the larger television sets such as fast response speed, low-cost electric power, wider visual angle display are sufficiently satisfied. The currently most widely studied display material, the Organic Light-emitting Diodes(OLEDs) overwhelms the Liquid Crystal Display(LCD), the main occupier of the market. This new material features a response speed of more than a thousand times faster, no need of backlight, a low driving voltage, and no limit of view angle. And the OLEDs has high luminance efficiency and excellent durability and environment resistance, quite different from the inorganic LED light source. The OLEDs with simple device structure and easy produce can be manufactured in various shapes such as a point light source, a linear light source, a surface light source. This will surely dominate the market for the next generation lighting and display device. The new display utilizes not the glass substrate but the plastic one, resulting in the thin and flexible substrate that can be curved and flattened out as needed. In this paper, OLEDs device was produced by changing thickness of Teflon-AF of hole injection material layer. And as for the electrical properties, the four layer device of ITO/TPD/$Alq_3$/BCP/LiF/Al and the five layer device of ITO/Teflon AF/TPD/$Alq_3$/BCP/Lif/Al were studied experimentally.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2609-2615
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• 2013

A series of fluorene-carbazole copolymers containing the pendant phosphor chromophore $Ir(absn)_2(acac)$ (absn: 2-(1-naphthyl)benzothiazole; acac: acetylacetone) were designed and synthesized via Yamamoto coupling. In the film state, these copolymers exhibited absorption and emission peaks at approximately 389 and 426 nm, respectively, which originated from the fluorene backbone. However, in electroluminescent (EL) devices, a significantly red-shifted emission at approximately 611 nm was observed, which was attributed to the pendant iridium(III) complex. Using these copolymers as a single emission layer, polymer light-emitting devices with ITO/PEDOT:PSS/polymer:DNTPD/TmPyPb/LiF/Al configurations exhibited a saturated red emission at 611 nm. The attached iridium(III) complex had a significant effect on the EL performance. A maximum luminous efficiency of 0.85 cd/A, maximum external quantum efficiency of 0.77, maximum power efficiency of 0.48 lm/W, and maximum luminance of 883 $cd/m^2$ were achieved from a device fabricated with the copolymer containing the iridium(III) complex in a 2% molar ratio.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.503-505
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• 2008

A host material containing tetraphenylsilane, 9-(4-triphenylsilanyl-(1,1'4,1")-terphenyl-4"-yl)-9H-cabazole (TSTC), was synthesized for green phosphorescent organic emitting diodes. $Ir(ppy)_3$ based OLEDs using TSTC host and DTBT (2,4-diphenyl-6-(4'yl)-1,3,5-triazine) hole blocking layer (HBL) showed the maximum external quantum efficiency of 19.8 %, the power efficiency of 59.4 lm and high operational stability with a half lifetime of 160,000 h at an initial luminance of $100\;cd/m^2$.