• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1343-1348
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• 2008

LEDs which have many merits are widely used in the field of light devices, and have rapidly replaced old light devices such as incandescent or fluorescent lamps. Long life, on the order of 50,000 to 100,000 hours, is one of the key features of light emitting diodes(LEDs) that has attracted the lighting community to this technology. High Power white LEDs have yet to demonstrate this capability. This paper planed accelerated life test that has two factor(temperature, current) and two levels. Finally, using ALTA programs, we estimated the common shape parameter of Weibull distribution, life-stress relationship, B10 life and accelerating factors.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.7-11
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• 2008

Future electric lights will be composed of white LEDs (Light Emitting Diodes). Indoor wireless optical communication systems utilizing white LED lights have been studying about it. Generally, plural lights are installed in room. Therefore, their optical path difference must be considered. In this paper, the influence of an optical path difference has been investigated and two approaches against this problem are introduced. One uses OOK-RZ (On-Off Keying, Return-to-Zero) coding and the other uses optical OFDM (Orthogonal Frequency Division Multiplexing). From the results of computer simulations, we have found that these approaches are feasible for the wireless optical communication systems utilizing white LED lights.

• 한국광학회지
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• 제25권5호
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• pp.254-261
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• 2014

본 논문에서는 일반적인 코팅형 형광체와 이격 형광체 등 두 가지의 형광체 구조가 적용된 백색 LED를 제작한 후 온도변화에 따라 각 백색 LED의 발광 특성이 어떻게 변하는지 측정, 비교하였다. 상온에서 80oC 사이의 구간에서 측정된 두 백색 LED의 발광 스펙트럼을 분석하기 위해 Gaussian Lorentz-cross product 함수와 Asymmectic double sigmoidal 함수를 각각 청색 피크와 황색 피크의 곡선맞춤에 활용하였다. 이로부터 각 피크의 중심파장과 진폭, 반치폭 및 비대칭성을 온도의 함수로 구할 수 있었다. 온도에 따른 휘도와 색좌표를 측정한 결과 이격형광체 구조의 백색 LED의 온도에 따른 휘도저하율 및 색좌표 변화율이 훨씬 적었다. 이는 청색 LED 칩과 형광체가 분리됨에 따라 형광체의 온도가 일반 형광체 도포형 LED의 경우에 비해 낮아져서 효율이 상승했고 아울러 형광체에서 발생한 빛의 칩에 의한 흡수가 감소했기 때문인 것으로 해석된다.

• 마이크로전자및패키징학회지
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• 제15권4호
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• pp.59-64
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• 2008

본 연구에서는 백색 고분자유기 발광다이오드를 제작하여 전기 광학적 특성을 평가하였다. ITO(indium tin oxide)를 양극으로 사용하고 정공수송층으로 PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)]를 발광물질로는 PFO [poly(9,9-dioctylfluorene)]와 MEH-PPV [poly(2-methoxy-5(2-ethylhexoxy)-1,4-phenyl-enevinyle)]를 각각 host와 dopant로 사용하였다. 전자주입층으로 LiF(lithium flouride)와 음극으로 Al(aluminum)을 증착하여 최종적으로 ITO/PEDOT:PSS/PFO:MEH-PPV/LiF/Al 구조를 갖는 백색 고분자 유기발광다이오드를 제작하고 PFO와 MEH-PPV의 농도에 따른 전기 광학적 특성 변화를 조사하였다. 제작된 소자는 9V에서(x=0.36, y=0.35)의 CIE 색좌표를 갖는 백색 발광이 관찰되었으며, 최대 전류밀도와 휘도는 약 13V의 인가전압에서 $740mA/cm^2,\;900cd/m^2$의 값을 나타내었으며, $200cd/m^2$ 휘도에서 0.37 cd/A의 최대 전류효율이 관찰되었다.

• 한국전기전자재료학회논문지
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• 제24권6호
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• pp.486-490
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• 2011

To investigate the effect of two-emission-layer structure on the emission characteristics of the phosphorescent white organic light-emitting diodes (PHWOLEDs), the PHWOLEDs with two different emission layers, blue EML(29 nm, FIrpic-doped mCP) and red EML(1 nm, Ir(pq)$_2$acac-doped CBP)), following host-guest system were fabricated. The bi-layered blue EML was composed of mCP:FIrpic (20 nm, 7 vol.%) and mCP:FIrpic (9 nm, 7, 10, 15, 20, and 25 vol.%, respectively). When the concentration of FIrpic was increased from 7 to 15 vol.%, light emission luminance, current efficiency, and external quantum efficiency were increased. On the contrary, when the concentration of FIrpic was increased to more than 20 vol.%, light emission luminance, current efficiency, and external quantum efficiency were decreased. The PHWOLEDs with the bi-layered blue EML structure of mCP:FIrpic (20 nm, 7 vol.%) and mCP:FIrpic (9 nm, 15 vol.%) showed current efficiency of 29.7 cd/A and external quantum efficiency (EQE) of 16.6% at 1,000 $cd/cm^2$.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.368-369
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• 2003

The recent development of InGaN-based white light emitting diodes (LEDs) has expanded their potential applications in areas such as white electric home appliances, backlight for mobile phone or notebook PC, and indoor lightings. In this lecture, recent researches related to the phosphors for LEDs applications and their luminescent properties were reviewed. PDPs are considered as the most potential flat panel displays with a large-screen size. Phosphors in PDPs directly affect the brightness and lifetime. So, many researchers have tried to improve the luminescence characteristics of the phosphors especially under vacuum ultraviolet (VUV) excitation. We overviewed recent research trends and conclusive achievements for the PDP phosphors.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1216-1219
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• 2009

Recently,electroluminescence devices based on organic semiconductors have made considerable progress. Displays based on organic light emitting diodes (OLED) are commercially available. To gain broader acceptance, the performance of OLED devices has to be further improved, in particular for lighting. This article discusses the possibility to use controlled electrical doping for improving the properties of devices and new approaches for highly efficient white OLED.

• 한국세라믹학회지
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• 제54권5호
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• pp.422-428
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• 2017

Single-phase yellow phosphor, $CaGd_{2-x}ZrSc(AlO_4)_3:xCe^{3+}$ ($CGZSA:Ce^{3+}$), possessing cubic symmetry with varied $Ce^{3+}$ concentrations, was synthesized using the solid-state reaction method. The samples were characterized using X-ray diffraction (XRD), excitation spectra, emission spectra, thermal quenching, and decay curves. The cubic phase of $CGZSA:Ce^{3+}$ phosphor was confirmed via XRD analysis. The photoluminescence spectra of $CGZSA:Ce^{3+}$ phosphor demonstrated that the phosphor could be excited at the wavelength of 440 nm; a broad yellow emission band was centered at 541 nm. These results indicate that the phosphors are adequately excited by blue light and have the potential to function as yellow-emitting phosphors for applications in white light-emitting diodes.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1055-1055
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• 2009

The mobility of charge carriers has been investigated in the pristine and phosphorescent materials doped host materials using time-of-flight photoconductivity technique. The field and temperature dependences of the mobility were analyzed with the Gaussian disorder model. Based on these results, we optimized white organic light emitting diodes (WOLEDs) consisting of multi-emitting layers doped with phosphorescent and fluorescent dopants. Especially, we studied the effect of each emitter position and an interlayer on the device characteristics of WOLEDs.

• Fisheries and Aquatic Sciences
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• 제18권2호
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• pp.211-220
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• 2015

We investigated the differences in the expression of the neurohormones kisspeptin (Kiss) and gonadotropin-inhibitory hormone (GnIH) and cytochrome P450 aromatase (P450arom), gonadotropin hormones (GTHs), and sex steroids in the goldfish Carassius auratus exposed to light-emitting diodes (LEDs). The expression levels of Kiss1, Kiss2, G-protein-coupled receptor 54 (GPR54), GTHs, GnIH, and P450arom were compared between the control (white light) and LED-treated goldfish. Furthermore, we measured the plasma levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The levels of Kiss1 mRNA and protein; Kiss2, GPR54, and $GTH{\alpha}$ protein; GTH mRNA; and plasma FSH and LH in the hypothalamus and cultured hypothalamus cells were significantly higher in the green and purple LED treatment groups than in the other groups. These results suggested that red LEDs inhibit the sex maturation hormones, Kiss, GPR54, GTHs, and P450arom, and that GnIH plays a role in the negative regulation of reproductive function in goldfish.