• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.627-627
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• 2013

Recently, most studies concerning inorganic CdSe/ZnS quantum dot (QD)-polymer hybrid LEDs have been concentrated on the structure with multiple layers [1,2]. The QD LEDs used almost CdSe materials for color reproduction such as blue, green and red from the light source until current. However, since Cd is one of six substances banned by the Restriction on Hazardous Substances (RoHS) directive and classified into a hazardous substance for utilization and commercialization as well as for use in life, it was reported that the use of CdSe is not suitable to fabricate a photoelectronic device. In this work, we demonstrate a novel, simple and facile technique for the synthesis of ZnO-graphene quasi-core.shell quantum dots utilizing graphene nanodot in order to overcome Cd material including RoHS materials. Also, We investigate the optical and structural properties of the quantum dots using a number of techniques. In result, At the applied bias 10 V, the device produced bluish-white color of the maximum brightness 1118 cd/$m^2$ with CIE coordinates (0.31, 0.26) at the bias 10 V.

• Korean Journal of Organic Agriculture
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• v.19 no.spc
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• pp.203-205
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• 2011

Investigation on oriental melon was carried out for 30 minutes starting at 7 PM every day from March 21 to May 24 to find out the effect of light emitting diode on seedling quality, grafting, growth and flowering of oriental melon. According to the result of the investigation, plant height was longer in Blue, Infrared, Red+Blue and Red treatment and leaf number was higher in Blue, Red+Blue and Infrared treatment than those of control. No big difference was identified between control and Yellow, Green, Ultraviolet treatments. Grafting rate was high in Green, Red+Blue and Green treatment. The number of flower every week in control was nine, the number was almost 1 higher in White and Ultraviolet A treatments, but it was 1 to 4 lower in the rest of treatments. The number of female flowers of control was 10, however, it was 21 in Infrared treatment, 17 in White, 15 in Ultraviolet, 13 in Red+lnfrared, 12 in Blue and Red+Blue, 11 in Yellow and 8 in Green.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.565-568
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• 2008

In this study, a blue-emitting $Sr_2MgSi_2O_7:Eu^{2+}$ (SMS) phosphor for white light-emitting diodes is reported. Through transition of $4f{\rightarrow}5d$ in $Eu^{2+}$, SMS showed a strong blue emission under UV excitation. Additionally, the variation of emission wavelength of SMS is explained by crystal field effect and is supported by rietveld refinement.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.12
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• pp.174-182
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• 2015

In this paper, we developed the small size RGB sensor that recognizes a long distance using a low-cost color sensor. Light receiving portion of the sensor was used as a camera lens for far distance recognition, and illuminating unit was increased the strength of the light by using a high-power white LED and a lens mounted on the reflector. RGB color recognition algorithm consists of the learning process and the realtime recognition process. We obtain a normalized RGB color reference data in the learning process using the specimens painted with target colors, and classifies the three colors using the Mahalanobis distance in recognition process. We apply the developed the RGB color recognition sensor to a prototype of the part classification system and evaluate the performance of its.

• Current Applied Physics
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• v.18 no.11
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• pp.1225-1229
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• 2018

In this paper, we investigated the electronic structures and defect states of $SrLaMgTaO_6$ (SLMTO) double perovskite structures by using resonant inelastic x-ray scattering. Recently, $Eu^{3+}$ doped SLMTO red phosphors have been vigorously investigated due to their higher red emission efficiency compared to commercial white light emitting diodes (W-LED). However, a comprehensive understanding on the electronic structures and defect states of host SLMTO compounds, which are specifically related to the W-LED and photoluminescence (PL), is far from complete. Here, we found that the PL spectra of SLMTO powder compounds sintered at a higher temperature, $1400^{\circ}C$, were weaker in the blue emission regions (at around 400 nm) and became enhanced in near infrared (NIR) regions compared to those sintered at $1200^{\circ}C$. To elucidate the difference of the PL spectra, we performed resonant inelastic x-ray spectroscopy (RIXS) at Ta L-edge. Our RIXS result implies that the microscopic origin of different PL spectra is not relevant to the Ta-related defects and oxygen vacancies.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.424-424
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• 2013

Ce3+, Sm3+, Eu3+, Tb3+ 등 희토류를 도핑한 여러 종류의 형광체는 백색 LED (white light-emitting diode), 전계방출표시소자(field emission display), 플라즈마디스플레이패널(plasma display panel), 약물 운송(drug delivery) 등 다양한 분야에서 응용되고 있다. 최근에는 졸-겔 방법(sol-gel method)을 이용하여Y2SiO5, Y3-XGdxAl5O12, SrAl2O4 등 여러 종류의 호스트 물질을 합성하여 형광체의 특성을 분석하는 연구가 활발히 진행되고 있다. 이러한 졸-겔 방법은 비교적 낮은 온도에서 간단한 공정으로 좋은 균질성과 높은 생산성을 갖도록 형광체를 제작할 수 있는 장점을 가지고 있다. 이에 본 연구에서는 졸-겔 방법을 이용하여 BaGd2TiO13구조를 제작하였고, 이러한 구조적, 광학적 특성을 분석하기 위하여 열분석기(thermal analyzer), 전계방출형주사전자현미경(field emission scanning electron microscopy), 투과전자현미경(field emission transmission electron microscopy)을 이용하였다. 이러한 졸-겔 방법을 이용하여 제작한 BaGd2TiO13 구조의 형광체 적용 연구를 통한 디스플레이 및 백색 LED 응용에 유용할 것으로 기대된다.

• Journal of Applied Reliability
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• v.12 no.4
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• pp.275-285
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• 2012

This paper presents a changes of luminescence property for converted white LEDs with the commercially available silicate phosphor. If silicate phosphor's quantity increase step by step. luminescence property will be changing. we analyze luminescence property for these change and carry out the high temperature aging test for 7,000 hours, the high temperature and humidity aging test for 7,000 hours for reliability. LED degradation not only results in reduced light output but also in color changes. so we monitor correlated color temperature (CCT), chromaticity coordinates(x, y) and spectrum intensity. Those results suggest that humidity factor more bad effect in color changes than temperature factor and Lighting quality is related with quantity of phosphor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.9
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• pp.577-582
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• 2017

The white light of a hybrid LED is obtained by using red and green organic fluorescent layers made of polymethylmethacrylate (PMMA) films, which function as color down-conversion layers of blue light-emitting diodes. In this research, we studied the fluorescence properties of a red organic fluorophore, employing perylene bisimide derivatives applicable to hybrid LEDs. The solubility, thermal stability, and luminous efficiency are important characteristics of organic fluorophores for use in hybrid LEDs. The perylene fluorescent compounds (1A and 1B) were prepared by the reaction of 4-bromophenol and 4-iodophenol with N,N'-bis(4-bromo-2,6-diisopropylphenyl)-1, 6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxyl diimide (1) in the presence of dimethyl formaldehyde (DMF) at $70^{\circ}C$. The synthesized derivatives were characterized by using $^1H-NMR$, FT-IR, UV/Vis absorption and PL spectra, and TGA analysis. Compounds 1A and 1B showed absorption and emission at 570 nm and 604 nm in the UV/Vis spectrum. We also documented favorable solubility and thermal stability characteristics of the perylene fluorophores in our work. Perylene fluorophore 1, with the 4-bromophenol substituent 1A, exhibited particularly good thermal stability and solubility in organic solvents.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.11-14
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• 2007

현재, 새로운 조명광원으로서 백색 LED가 기대되고 있으며, 이를 이용하는 조명이 확대되어 실용화 될 것으로 예상된다. LED 광원을 이용하여 조명기구를 제작하고 이것을 실내조명으로 사용할 때 조명기구에 의한 글레어가 편안함을 주는지 불편함을 주는지에 대한 평가가 요구된다. 실내 조명환경에 대한 불쾌글레어를 평가하기 위해 UGR(Unified Glare Rating)을 추천하고 있다. 그러나 균일한 글레어 광원의 평균휘도를 이용하여 계산된 종래의 불쾌글레어 평가법들은 불균일한 휘도를 갖는 LED 조명기구에 대해서는 적용하기 어렵게 될 것으로 판단된다. 그래서 UGR를 이용하였을 경우, 균일한 휘도를 갖는 조명기구와 불균일한 휘도를 갖는 조명기구에 대해서 어떠한 차이가 있는지 다음의 불쾌글레어의 주관평가 실험을 수행하였다. 평균휘도가 같고 최대 휘도와 최소 휘도가 다른 조명기구(균일한 휘도를 갖는 조명기구 1종과 불균일한 휘도를 갖는 조명기구 2종)를 글레어 광원으로 사용하였다. 입체각(${\omega}$)과 위치지수(Position Index)를 고정시키고 배경휘도($L_b$)와 광원휘도($L_s$)를 임의로 변화시켰다. 주어진 환경에서 피험자로 하여금 얼마나 편안하진 또는 불편한지에 대한 느낌을 값으로 평가하도록 하였다. 우선, UGR과 주관평가 사이에 차이가 나타났으며, 이는 동 서양에 따른 문화적 및 생리적 차이에 기인한다고 생각된다. 다음으로 균일한 휘도를 갖는 조명기구보다 불균일한 휘도를 갖는 LED 조명기구가 더 높은 값을 할당 받아 LED 조명기구가 불쾌감을 더 유발시키는 것으로 나타났다. 또한 LED 소자 간격에 따른 영향은 글레어 광원의 휘도가 높아질수록 크게 나타났으며, 배경휘도에 대해서도 광원의 휘도가 높아질수록 LED 소자 간격의 차이에 의한 영향이 나타났다. 따라서 UGR식은 균일한 휘도를 갖는 조명기구에 적용하기에는 적합하지만, 불균일한 휘도를 갖는 조명기구에 적용하기에는 부적합하다고 판단된다.

• Korean Journal of Environmental Agriculture
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• v.32 no.2
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• pp.123-127
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• 2013

BACKGROUND: The incandescent bulb and compact fluorescent lamp are widely using as a light sources for daylength extension of chrysanthemum. But, these light sources consume a lot of electricity and have short longevity. A light-emitting diode (LED) is a semi conductor light source. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime. In this study, we investigated the intensity of red light to control flowering of chrysanthemum (Dendranthema grandiflorum cv. "Shinma") by using LEDs. METHODS AND RESULTS: The red (660 nm) and far-red (730 nm) light were irradiated subsequently to investigate photo-reversible flowering responses of chrysanthemum. The flowering of chrysanthemum was inhibited by night interruption with red light but subsequently irradiated far-red light induced the flowering of chrysanthemum. This photoreversibility, reversion of the inductive effect of a brief red light pulse by a subsequent far-red light pulse, is a property of photo responses regulated by the plant photoreceptor phytochrome B. Four different intensity of red light of 0.7, 1.4, 2.1, and $2.8{\mu}mol/m^2/s$ (PAR) were irradiated at growth room in order to determine the threshold for floral inhibition of chrysanthemum. Over $1.4{\mu}mol/m^2/s$ of the red lights irradiated chrysanthemums were not flowered. The plant length, fresh weight, number of leaves, and leaf area of chrysanthemum irradiated with red light were increased by 17%, 36%, 11%, and 48%, respectively, compared to those of compact fluorescent lamp. CONCLUSION(S): The red light and subsequential far-red light showed that the photoreversibility on flowering of chrysanthemum. The red light ($1.4{\mu}mol/m^2/s$ of red LEDs) and white light (50 Lux of compact fluorescent lamp) have the same effect on inhibition of flowering in chrysanthemum. Additionally, the red light increased the plant height and dry weight of chrysanthemum.