• Journal of the Korea Furniture Society
• /
• v.26 no.4
• /
• pp.428-434
• /
• 2015

In this study, we received each wood plastic composites (WPC) from three manufacturers. These WPCs were evaluated regarding their physical and mechanical properties of both before and after accelerated weathering by ultraviolet (UV) irradiation. The total time of exposure of the WPCs to UV irradiation was 1800 h. The water absorption, volumetric swelling and shrinkage of WPCs did not affected by UV irradiation. Among the mechanical properties, there was no significant differences in bending strength and screw withdrawal resistance of UV treated WPCs compared with those of reference WPCs. However, surface hardness of WPCs showed decrease under UV irradiation. Stereoscopic microscopy observation revealed deterioration of the surface layer polymer in all weathered WPCs by UV. Exposure of the WPCs to UV irradiation caused decomposition and disappearance of the polymer layer. From this result, we can estimate that damage of polymer by UV led to a decrease in the surface hardness of the WPCs. The wood flours retained original shape after accelerated weathering by UV irradiation.

• Journal of the Korean Ceramic Society
• /
• v.41 no.8
• /
• pp.573-577
• /
• 2004

We have synthesized a Eu$^{2＋}$-activated Sr$_3$MgSi$_2$ $O_{8}$ blue phosphor and investigated an attempt to develop blue LEDs by combining it with a InGaN blue LED chip (Len=405 nm). The InGaN-based Sr$_3$MgSi$_2$ $O_{8}$：Eu LED Lamp shows two bands at 405 nm and 460 nm. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This 405 nm emission was used as an optical transition of the Sr$_3$MgSi$_2$ $O_{8}$：Eu phosphor. The 460 m emission band is ascribed to a radiative recombination of Eu$^{2＋}$ impurity ions in the Sr$_3$MgSi$_2$ $O_{8}$ host matrix. As a consequence of a preparation of W blue LED Lamp using the Sr$_3$MgSi$_2$ $O_{8}$：Eu blue phosphor, the highest luminescence efficiency was obtained at the ration of epoxy/blue phosphor(1/0,202). At this time, the CIE chromaticity was x=0.1417 and y=0.0683.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2008.10a
• /
• pp.97-99
• /
• 2008

본 논문은 고출력 LED를 이용하여 대한민국 경찰청 및 지방경찰청 과학수사에 사용하는 지문감식을 위한 효과적인 휴대용 교광원에 관한 연구이다. 최근 광반도체(光半導體) 관련 형광물질 등 원천기술의 획기적인 R&D가 진행 중에 있다. 따라서 본 논문에서는 산업체는 물론 생활주변에 사용되는 핸드폰 백라이트, LED 평면광원, 가로등용 LED광원, 오징어잡이에 사용되는 집어용 LED, OLED, CNT 광원 등에 적용되는 기술을 광학적 논리를 근거로 하여 고고학에 적용되는 문화재, 미술품의 진품감정, 지문현출을 통한 지문감식 등에 적용하기 위한 연구이다. 미국 유럽 남미 등에서 개발하여 과학수사에 사용하고 있는 교광원은 기동성 및 휴대하기에 매우 무겁고 고가이다. 이러한 문제점을 해결하기 위해 LED 신광원 UV 파장을 이용하여 지문현출 및 지문감식 등에 적용하면 소형경량화가 가능하여 무게와 부피를 급감할 수 있으며, 휴대가 간편하여 기동성이 뛰어나고 신속정확하게 매우 효과적으로 감정 및 감식이 가능하여 그 기대 효과가 매우 우수하다. 이러한 장점을 조명공학 및 광학적 이론을 근거로 지속적인 연구개발을 추진하여 국산화된 세계적인 신제품 개발을 위해 타당성을 검토 고찰하였다.

• Journal of Sensor Science and Technology
• /
• v.16 no.1
• /
• pp.7-10
• /
• 2007

A thick film catalytic gas sensors which can be operated at $142^{\circ}C$ in presence of ultra violet-light emitting diode has been developed to measure hydrogen concentration in 0-5 % range. The sensing material as a combustion catalyst consists of $TiO_{2}$ (5 wt%) and Pd/Pt (20 wt%) supported on $Al_{2}O_{3}$ powder and the reference material to compensate the heat capacity of it in a bridge circuit was an catalyst free $Al_{2}O_{3}$ powder. Platinum heater and sensor materials were formed on the alumina plate by screen printing method and heat treatment. The effect of UV radiation in the presence of photo catalyst $TiO_{2}$ on the sensor sensitivity, response and recovery time has been investigated. The reduction of operating temperature from $192^{\circ}C$ to $142^{\circ}C$ for hydrogen gas sensing property in presence of UV radiation is attributed to the hydroxy radical and superoxide which was formed at the surface of $TiO_{2}$ under UV radiation.

• Journal of Bio-Environment Control
• /
• v.20 no.3
• /
• pp.182-188
• /
• 2011

This research was conducted to evaluate the effect of supplemental light-emitting diode (LED) light on growth characteristics and phytochemical content of pepper (Capsicum annuum L.) seedling using LED blue (470 nm, B), red (660 nm, R), blue + red (BR), far red (740 nm, FR) and UV-B (300 nm) light treatment, and without artificial light. Photon flux of LED light was 49, 16, 40, 5.0 and $0.82{\mu}mol\;m^{-2}s^{-1}$ for B, R, BR, FR, and UV-B light, respectively, during experiment. Supplemental LED light duration was $16hr\;day^{-1}$ and UV-B light duration was 10 min. per day after sunset up to 15 days (12 days after germination) of plants age. In our research, growth characteristics and phytochemical content of pepper seedlings were greatly influenced by supplemental LED light compare to control treatment. Red light increased the number of leaves, number of nodes, leaf width and plant fresh weight by 34%, 27%, 50% and 40%, respectively. Blue light increased the leaf length by 13%, and stem length and length of inter node were increased by 17% and 34%, respectively under grown far red light. After 15 days of light treatments phytochemical concentrations of pepper plants were significantly changed. Blue light enhanced the total anthocyanin and chlorophyll concentration by 6 times and 2 times, respectively. Red light increased the total phenolic compound at least two folds meanwhile far red light reduced the ascorbic acid and antioxidant activity 31% and 66%, respectively compared to control treatment.

• Journal of the Korean Chemical Society
• /
• v.50 no.3
• /
• pp.237-242
• /
• 2006

Nowadays, LEDs has been applied to the luminescent devices of various fields because of the invention of high efficient blue chip. Recently, especially, the white LEDs composed of InGaN blue chips and a yellow phosphor (YAG:Ce3+) have been investigated extensively. With the exception of YAG:Ce3+ phosphor, however, there are no reports on yellow phosphor that has significant emission in the 450~470 nm excitation range and this LED system is the rather low color rendering index due to their using two wavelength. Hence, we have attempted to synthesize thiogallate phosphors that efficiently under the long wavelength excitation range in the present case. Among those phosphors, we have synthesized Sr2Ga2S5:Eu2+ phosphor by change the host material of SrGa2S4:Eu2+ which is well known phosphor and we investigated the luminescent properties. In order to obtain the harmlessness and simplification of the synthesis process, sulfide materials and mixture gas of 5 % H2/95 % N2 were used instead of the CS2 or H2S gas. The prepared phosphor shows the yellow color peaking at the 550 nm wavelength and it possible to emit efficiently under the broad excitation band in the range of 300~500 nm. And this phosphor shows high luminescent intensity more than 110 % in comparison with commercial YAG:Ce3+ phosphor and it can be applied for UV LED due to excitation property in UV region.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.32 no.1
• /
• pp.86-92
• /
• 2019

Although perylene bisimide derivatives have advantages such as excellent thermal stability and high luminance efficiency, they have poor solubility characteristics in organic solvents. In this research, in order to improve the solubility characteristics, we prepared perylene bisimide derivatives (1C) and (2C) with swallow-tail substituted imide, which is known to lead to excellent solubility. The structures and properties of swallow-tail perylene bisimide (1C) and (2C) were analyzed by $^1H-NMR$, FT-IR, UV/Vis spectroscopy, and thermogravimetric analysis (TGA). The maximum absorption wavelengths of (1C) and (2C) in the UV/Vis spectrum were 558 nm and 556 nm, respectively, and the maximum emission wavelengths were 602 nm and 600 nm, respectively. In the TGA, (1C) demonstrated good thermal stability with less than 5 wt% weight loss up to $242^{\circ}C$. In the solubility test, (1C) and (2C) exhibited solubilities of more than 5 wt% in chloroform, ethyl acetate, and dimethylformamide, but not in methanol. When the compounds (1C) and (2C) were mixed with PMMA (polymethyl methacrylate), thin films showed peaks at 679 nm and 677 nm, respectively, in the photoluminescence spectra. (1C) was found to be a possible candidate as red organic phosphor for hybrid LEDs.

• Journal of Food Hygiene and Safety
• /
• v.36 no.5
• /
• pp.447-453
• /
• 2021

In this study, the effectiveness of physical control technology, a combined light sterilization (LED, UV) and hot water treatment in reducing Aspergillus ochraceus for food production environment was investigated. In brief, 1 mL aliquot of A. ochraceus spore suspension (10^7-8 spore/mL) was inoculated onto stainless steel chips, which was then dried at 37℃, and each was subjected to different physical treatment. Treatments were performed for 0.5, 1, 2, 5, 8, and 11 hours to reduce the strains using a light-emitting diode, but no significant difference was confirmed among the treatments. However, a significant reduction was observed on the chips treated with UV-C exposure and hot water immersion. After being treated solely with 360 kJ/m² of UV-C on stainless steel chip, the fungi were significantly reduced to 1.27 log CFU/cm². Concerning the hot water treatment, the initial inoculum amount of 6.49 log CFU/cm² was entirely killed by immersion in 83℃ water for 5 minutes. Maintaining a high temperature for 5 minutes at the site is difficult. Thus, considering economic feasibility and usability, we attempted to confirm the appropriate A. ochraceus reduction conditions by combining a relatively low temperature of 60℃ and UV rays. With the combined treatments, even in lukewarm water, A. ochraceus decreased significantly through the increases in the immersion time and the amount of UV-C irradiation, and the yield was below the detection limit. Based on these results, if work tools are immersed in 60℃ lukewarm water for 3 minutes and then placed in a UV sterilization device for more than 10 minutes, the possibility of A. ochraceus cross-contamination during work is expected to be reduced.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.26 no.2
• /
• pp.45-54
• /
• 2008

We have manufactured a photoresist which has excellent dispersity and good applying property due to 330 cps of viscosity for environment-friendly and economical maskless screen plate making. And the photoresist applied on the screen stretched was exposed with mask by UV-LED light source so we could manufacture the photoresist which proper for the UV light source. And it was developed by air spray with $1.7\;kgf/cm^2$ of injection pressure. Because of the excellence of power and resolution of the UV-LED light sourse, the pencil hardness and solvent resistance of curing photoresist film were excellent as those of conventional photoresist film. Moreover the $100{\mu}m$-width stripe image which has sharp edges was formed. So we confirmed a possibility of dry development process by air spray method.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.28 no.1
• /
• pp.65-75
• /
• 2010

Environmentally friendly, stencil and screen printing for cost-effective for maskless. In this study, UV -LED light source for the dispersion characteristics and high competence photoresist coating was prepared. Wavelength of 365nm UV-LED exposure device using the maskless lithography, 1.7kgf/$cm^2$ $2600mmH_2O$ the injection pressure and the suction pressure by using a dry photoconductor symptoms were dry emulsion on the market as a result, curing properties and adhesion, hardness, solvent resistance and excellent reproduction of fine patterns and ecological stencil technology was available and could be confirmed as a possibility.