• Journal of Advanced Marine Engineering and Technology
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• v.39 no.1
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• pp.63-67
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• 2015

White light-emitting diode (WLED) is growing interest in using both illumination and communications. This paper reports visible light communication (VLC) composed of a super bright white light-emitting diode, low cost commercial photo-diode and a Fresnel lens. LED driver is consisted of the power MOSFET and MOSFET driver that switches the LED on and off. The modulation bandwidth of the LED used was determined to be 8 MHz. However, it was possible to communicate up to 1 Mbps under illumination of 500 lx because of the weak signal power and a low spectral sensitivity of the SHF213 as a PIN photodiode. In order to enhance the system bandwidth, the LED light was focused on the PIN photodiode by use of the Fresnel lens. As a result of that, visible light link was operated up to modulation bandwidth of the LED. The signal to noise ratio can be improved by 40 dB using an optical concentration at the receiver.

• Korean Chemical Engineering Research
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• v.49 no.3
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• pp.320-324
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• 2011

TOPO/TOP capped CdSe nanoparticles were synthesized via thermal-solvent method. The 540 nm green and 620 nm red emitting CdSe nanoparticles were obtained by controlling the reaction time and temperature. Phosphor conversion white LED was produced combining a 460 nm emitting InGaN LED chip as an excitation source with 540 and 620 nm CdSe nanoparticles as phosphors. The single or double phosphor layer was fabricated by mixing with epoxy, and investigated the effects on the luminous properties of the white LED. The single phosphor layer white LED showed 5.78 lm/W with CIE of (0.36, 0.45) in reddish white, and the double phosphor layer white LED showed 7.28 lm/W with that of (0.32, 0.34) in pure white at 20 mA. When the 400 nm near-UV LED was applied to optical pumping source, the luminous efficiency of white LED was enhanced to 8.76 lm/W.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.2
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• pp.309-314
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• 2012

In this paper, we present surface-to-underwater visible light communication systems using white LEDs. Pulse position modulation (PPM)-based analogue data communications and on-off keying-based digital data communications systems are developed. Inexpensive and commercial power-LEDs and photo-diodes are used to construct two types of systems. We report the experimental results obtained from the prototype systems to show the possibility of an optical underwater visible light transceiver as a basis for short range underwater wireless network. Their performance deteriorates more than the atmosphere's one because of attenuation and scattering of the light in water, but these results are promising for the potential to create more robust network interface that improve medium performance such as a LED modulation and a photo-detector demodulation.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.191.1-191.1
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• 2015

최근에 백색 발광다이오드를 개발하기 위한 고효율의 형광체 개발에 많은 연구가 집중되고 있다. 본 연구에서는 $La_2WO_6$ 모체 결정에 다양한 활성제 이온인 $Eu^{3+}$, $Dy^{3+}$, $Sm^{3+}$, $Tb^{3+}$를 각각 도핑하여 다양한 발광 파장을 갖는 고효율의 형광체를 제조하였다. 합성한 형광체 분말은 초기물질 $La_2O_3$, $WO_3$, 희토류 원소 ($Eu_2O_3$, $Dy_2O_3$, $Sm_2O_3$, $Tb_4O_7$)를 각각 화학양론적으로 준비하여 고상반응법으로 제조하였으며, 이때 하소 공정은 $400^{\circ}C$에서 3시간, 소결 공정은 $1050^{\circ}C$에서 5시간 유지하여 합성하였다. $La_2WO_6:Eu^{3+}$ 형광체 분말의 경우에 320, 395, 465 nm에서 강한 흡광 파장이 발생하였으며, 파장 320 nm로 여기 시켰을 때 최대 발광 세기는 618 nm에서 관측되었다. $Sm^{3+}$을 도핑한 형광체의 흡광 스펙트럼은 310, 375, 406, 475 nm에서 발생하였으며, 310 nm로 여기 시켰을 때 602 nm의 강한 주황색 발광 신호가 나타났다. $Dy^{3+}$가 도핑된 $La_2WO_6$ 형광체는 575 nm에 강한 발광 피크를 갖는 황색을 나타내었으며, 흡광 파장은 313 nm 이었다. $Tb^{3+}$를 도핑한 형광체의 주 흡광 스펙트럼은 316 nm에서 발생하였고, 발광 스펙트럼은 545 nm에 피크를 갖는 녹색 발광 신호가 나타났다. 활성제이온의 종류에 따른 형광체의 흡광과 발광, 결정 구조의 특성을 체계적으로 제시하고자 한다.

• Journal of the Korean GEO-environmental Society
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• v.12 no.12
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• pp.31-35
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• 2011

The purpose of this study was to determine optimum condition for the cultivation of Chlorella sp. FC-21, which is a freshwater microalgae, using light emitting diodes (LEDs). Specific growth rate and cell concentration were measured for the reactors at the illumination of different wavelengths of LEDs. Among various types of LEDs, red LEDs were the most effective light source, and also greatest increases of specific growth rate and cell concentrations were obtained when light intensity of red LEDs increased. From this study, we found that red LEDs were the most appropriate light source for the cultivation of Chlorella sp. FC-21.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.5
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• pp.204-209
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• 2007

We synthesized a series of $CaS_{1-x}Se_x:Eu$ red-emitting phosphors for application in phosphor-converted three-band white light emitting diode(LED). The photoluminescence and structural properties of $CaS_{1-x}Se_x:Eu$ were examined. The $CaS_{1-x}Se_x:Eu$ phosphors have a strong absorption at 455 nm, which is the emission wavelength of a blue LED. CaS:Eu has a red omission peak at 651 nm due to the $4f^65d^1(T_{2g}){\rightarrow}4f^7(^8S_{7/2})$ transition of the $Eu^{2+}$. The emission peak of $CaS_{1-x}Se_x:Eu$ is shifted from 651 to 598 nm with increasing Se content. $CaS_{1-x}Se_x:Eu$ can be used as wavelength-tunable red-emitting phosphors pumped by a blue LED. We also fabricated a three-band white LED by doping $SrGa_2S_4:Eu$ and $CaS_{0.50}Se_{0.50}:Eu$ phosphors onto a blue LED chip.

• 기계와재료
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• v.21 no.2
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• pp.110-118
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• 2009

최근 유력한 차세대 광원으로 떠오르고 있는 발광 다이오드(LED, light emitting diode)는 화합물 반도체의 특성을 이용해 전기를 자외선, 가시광선, 적외선 등으로 전환시키는 반도체 소자로 에너지 효율이 매우 높고, 수명이 길어 교체 비용이 적으며, 진동이나 충격에도 강하고, 수은 등 유독물질의 사용이 불필요하기 때문에 에너지 절약, 환경보호, 비용절감 차원에서 매우 유리하다. 현재 LED 분야에 있어 주로 연구개발이 진행되고 있는 분야는 조명용 백색 LED 분야 및 디스플레이 소자 분야이다. LED를 이용한 백색 조명 및 디스플레이 기기의 개발을 위해서는 그 응용 분야에 맞는 효율이 우수한 형광체의 개발이 필수적이다. 본고에서는 현재 조명용 백색 LED 및 디스플레이 분야에 응용되는 형광체의 개발 현황을 위해 주로 연구동향을 분석하였다.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.216-220
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• 2014

We have synthesized a $CaMgSi_2O_6:Eu^{2+}$ blue phosphor via a solid-state reaction method. The $CaMgSi_2O_6:Eu^{2+}$ phosphor has monoclinic structure with a space group of C2/c (15), and an emission band peaking at 450 nm (blue) due to the $4f^7-4f^65d$ transition of the $Eu^{2+}ion$. The emission intensity at $100^{\circ}C$ is 54% of the value at room temperature. A white LED was fabricated by integrating a UV LED (400 nm) with our blue phosphor plus two commercial green and red phosphors. The white LED shows a color temperature of 3500 K with a color rendering index of 87 (x = 0.3936, y = 0.3605), and a luminous efficiency of 18 lm/W. The white LED shows a luminance maintenance of 97% after operation at 350 mA for 400 hours at $85^{\circ}C$.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.459-465
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• 2012

We had synthesized a green dopant material based on the binaphthyl group, 7,7'-(2,2'dimethoxy-1,1'-binaphthyl-3,3'-diyl) bis(4-(thiophen -2-yl) benzo[e][1,2,5] thiadiazole (TBT). We also fabricated the white organic light emitting diode (OLED) with a phosphorescent blue emitter : iridium(III)bis[(4,6-di-fluoropheny)-pyridinato -N,C2]picolinate (FIrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) of hole transport type host material and both TBT and bis(2-phenylquinolinato)- acetylacetonate iridium(III) (Ir(pq)2acac) doped in 1,3,5-tris(N-phenylbenzimidazole -2-yl)benzene (TPBi) of electron transport type host material. As a result, the property of white OLED using TBT, which demonstrated a maximum luminous efficiency and external quantum efficiency of 5.94 cd/A and 3.23 %, respectively. It also showed the pure white emission with Commission Internationale de I'Eclairage (CIE) coordinates of (0.34, 0.36) at 1000 nit.

• Proceedings of the Korean Vacuum Society Conference
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• 2006.02a
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• pp.139-139
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• 2006