• Journal of Sensor Science and Technology
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• v.32 no.6
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• pp.391-402
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• 2023

Low-dimensional (zero-dimensional (0-dim), 2-dimensional (2-dim)) nanoparticles, such as chalcogenide compound semiconductors, III-V semiconductors, transition metal dichalcogenides (TMDs), II-VI semiconductors, nanocarbons, hybrid quantum dots (QDs), and perovskite QDs (PQDs), for which blue light emission has been observed, are reviewed. Current synthesis and device fabrication technologies as well as their prospective applications on next-generation quantum-dot-based light-emitting diodes are discussed.

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.280-287
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• 2011

The heat temperature of a light emitting diode (LED) is investigated with the thermoelectric device (TED). The Peltier effect of the thermoelectric device is used to control the heat radiation and the junction temperature of high-power LEDs. For the typical specific current (350 mA) of high-power (1 W) LEDs, the LED temperature and the p-n junction temperature become $64.5^{\circ}C$ and $79.1^{\circ}C$, respectively. For 0.1~0.2 W driving power of TED, the LED temperature and the junction temperature are reduced to be $54.2^{\circ}C$ and $68.9^{\circ}C$, respectively. As the driving power of the TED increases over 0.2 W, the temperature of LED itself and the junction temperature are increased due to the heat reversed from the heat-sink to LED. As the difference of temperature between LED and the heat-sink is increased, the quantity of reversed heat becomes larger and it results to degrade the cooling capability of TED.

• Ocean and Polar Research
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• v.39 no.2
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• pp.107-114
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• 2017

In this study, we investigated the effects of light spectra on physiology stress and DNA damage in juvenile rock bream (Oplegnathus fasciatus) using light-emitting diodes (LEDs; green, 520 nm; red, 630 nm) at two intensities (0.25 and $0.5W/m^2$ ) with application of thermal stress (25 and $30^{\circ}C$). We measured the mRNA expression of heat shock protein 70 (HSP70) and the levels of plasma cortisol, glucose, aspartate aminotransferase (AspAT), and alanine aminotransferase (AlaAT). Additionally, DNA damage was measured using comet assays. Our findings showed that HSP70 mRNA expression and plasma cortisol, glucose, AspAT, and AlaAT levels were significantly higher after exposure to high temperatures and were significantly lower after exposure to green LED light. Thus, although high water temperatures induced stress in juvenile rock bream, green LED light inhibited stress. In particular, green LED light reduced stress and DNA damage to a greater degree than other light sources.

• Journal of Bio-Environment Control
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• v.21 no.3
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• pp.180-185
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• 2012

The objective of this study was carried out to elucidate the effect of LEDs (light emitting diodes) irradiation in relation to early growth and inorganic elements in leaf lettuce (Lactuca sativa L. 'Rollo Rosa'). In morphological changes of leaves, shoot elongation and hypocotyl length showed poor growth in red light irradiation, while the red + blue light irradiation induced shorter plant height and much greater leaf numbers resulting in increased fresh weight. In change of the Hunter's color and SPAD values, lettuce seedlings grown under in red + blue and fluorescent light irradiation had a higher $a^*$ value, otherwise SPAD values were not changed in these light irradiations. Interestingly, relative chlorophyll contents showed 1.8 times increased redness in the treatment of red + blue light irradiation. Inorganic element (N, Ca, Mg, Mn, and Fe) and ascorbic acid contents were increased in lettuce plants grown under LEDs light irradiation compared to those of lettuce grown under the fluorescent light which showed higher P and Mn contents. In conclusion, it is considered that red + blue light irradiation which stimulates growth and higher nutrient uptake in leaf lettuce could be employed in containers equipped with LEDs.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.6
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• pp.852-857
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• 2010

In this paper, we proposed and demonstrated an indoor visible-light communication system using an array of light-emitting diodes (LEDs). The main idea is based on that the LEDs can be used not only for lighting but also for free-space optical communications. Because LEDs offer advantageous properties such as high brightness, reliability, lower power consumption and long lifetime, the indoor visible-light communication systems are going to provide high quality of service by the high radiation power of the LED lighting. Prototype of simplex channel for audio and the full-duplex channel for text message were developed. Results indicates the viability of creating inexpensive free-space optical communication transceivers that might be embedded in commercial light products to supports indoor wireless networking.

• Journal of information and communication convergence engineering
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• v.19 no.4
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• pp.269-275
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• 2021

Light-emitting diodes (LEDs) are modulated using a square wave pulse sequence for flicker prevention and dimming control in visible light communication (VLC). In a VLC transmitter, the high and low bits of the non-return-to-zero (NRZ) data are converted to two square waves of different frequencies, which continue for a finite time defined by the fill ratio in an NRZ bit time. As the average optical power was kept constant and independent of data transmission, the LED was flicker-free. Dimming control is carried out by changing the fill ratio of the square wave in the NRZ bit time. In the experiments, the illumination of the LED light was controlled in the range of approximately 19.2% to 96.2% of the continuous square wave modulated LED light. In the VLC receiver, a high-pass filter combined with a latch circuit was used to recover the transmitted signal while preventing noise interference from adjacent lighting lamps.

• Horticultural Science & Technology
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• v.30 no.1
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• pp.6-12
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• 2012

Early growth, pigmentation, protein content, and phenylalanine ammonia-lyase (PAL) activity of red curly lettuces (Lactuca sativa L.) grown under different lighting conditions were investigated. Fluorescent lamps (control), blue, red, and blue plus red light-emitting diodes (LEDs) were used as light sources for 10 days. An equal proportion (1:1) of blue and red LEDs was used in the mixed radiation condition. Compared with the control, monochromic red or blue lighting increased fresh and dry weights of 'Ttuksum' and 'Jaju' lettuces. Anthocyanin synthesis was also significantly promoted by the mixed radiation of blue and red LEDs. The mixed radiation also increased the protein content and PAL enzyme activity of 'Ttuksum' leaves by about 200% compared to other treatments. Anthocyanin content was the highest in lettuces subjected to the mixture radiation of blue and red light treatment, while anthocyanin synthesis was inhibited by monochromic red light. The results of the present study indicate that growth and pigment synthesis in lettuces are significantly enhanced by exposure to mixed radiation from blue and red LEDs.

• Current Optics and Photonics
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• v.1 no.4
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• pp.289-294
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• 2017

A high-performance time-division multiplexing (TDM) -based multiuser (MU) multiple-input multipleoutput (MIMO) system for efficient indoor visible-light communication (VLC) is presented. In this work, a MIMO technique based on RGB light-emitting diodes (LEDs) with selection combining (SC) is utilized for data transmission. That is, the proposed scheme employs RGB LEDs for parallel transmission of user data and transmits MU data in predefined slots of a time frame with a simple and efficient design, to schedule the transmission times for multiple users. Simulation results demonstrate that the proposed scheme offers an approximately 6 dB gain in signal-to-noise ratio (SNR) at a bit error rate (BER) of $3{\times}10^{-5}$, as compared to conventional MU single-input single-output (SISO) systems. Moreover, a data rate of 66.7 Mbps/user at a BER of $10^{-3}$ is achieved for 10 users in indoor VLC environments.

• Journal of the Optical Society of Korea
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• v.19 no.3
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• pp.311-316
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• 2015

We investigate the temperature dependence of the phosphor conversion efficiency (PCE) of the phosphor material used in a white light-emitting diode (LED) consisting of a blue LED chip and yellow phosphor. The temperature dependence of the wall-plug efficiency (WPE) of the blue LED chip and the PCE of phosphor are separately determined by analyzing the measured spectrum of the white LED sample. As the ambient temperature increases from 20 to $80^{\circ}C$, WPE and PCE decrease by about 4.5% and 6%, respectively, which means that the contribution of the phosphor to the thermal characteristics of white LEDs can be more important than that of the blue LED chip. When PCE is decomposed into the Stokes-shift efficiency and the phosphor quantum efficiency (QE), it is found that the Stokes-shift efficiency is only weakly dependent on temperature, while the QE decreases rapidly with temperature. From 20 to $80^{\circ}C$ the phosphor QE decreases by about 7% while the Stokes-shift efficiency changes by less than 1%.

• Ceramist
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• v.21 no.1
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• pp.24-43
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• 2018

Organic-inorganic halide perovskite materials have attracted significant attention during the last few years because of their superior properties for electronic and optoelectronic devices, such as their long charge carrier diffusion lengths and high photoluminescence quantum yields of up to 100% with tunable bandgaps over the entire visible spectral range. In addition to solar cells, light emitting diodes (LEDs) represent a fascinating application for halide perovskite materials. In this study, we review the recent progress in halide perovskite LEDs. The current strategies for improving the performance of halide LEDs, focusing on morphological engineering, dimensional engineering, compositional engineering, surface passivation, interfacial engineering, and the plasmonic effect are discussed. The challenges and perspectives for the future development of halide perovskite LEDs are also considered.