• Journal of the Korean GEO-environmental Society
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• v.13 no.10
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• pp.63-68
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• 2012

This study was performed to determine optimum conditions of batch type cultivation of Isochrysis galbana cultivated under various wavelengths of light emitting dioes (LEDs). Among LEDs used in the cultivation, white LED was found to be the most effective light source, and light intensity of 3,000Lux resulted in the most effective for the cultivation of Isochyrysis galbana. Comparison with common light source, fluorescent light, showed less effective than that with white LED. Four different air flow rates were tested to overcome shading effects due to denser cell concentration in the solution. In results, cell growth rates and maximum cell concentrations were similar regardless of air flow rates. Three times greater cell concentrations, however, were observed when air was applied.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1343-1346
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• 2008

$KSrPO_4$ and $Sr_3(Al_2O_5)Cl_2$ phosphors doped with $Eu^{2+}$ emit a blue and orange-yellow luminescence under ultraviolet (UV) excitation at ~ 400 nm, respectivel, which can be used for making white light emitting diodes.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.289-290
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• 2007

We have theoretically derived a electrical model and extracted a parasitic parameters of leakage current in InGaN/GaN light emitting diodes (LEDs). The parasitic parameters of our LED are $R_p=10^{10}{\Omega}$, $I_{0,2}=10^{-17}A$ and $n_2=3.6$, which provide information of leakage current.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.93-94
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• 2008

In order to suppress the current crowding in light emitting diodes (LEDs) grown on sapphire substrate, the effect of nonuniform contact resistivity between TME layer and p-GaN layer on the LED surface was theoretically investigated. The analysis results showed that current crowding occurring around p-electrode could be considerably improved, which in turn would be helpful to improve the electrostatic discharge (ESD) characteristic.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.537-546
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• 2023

Intrinsically stretchable light-emitting diodes, composed of stretchable electrodes, charge transport layers, and luminescent materials, have garnered significant interest for enhancing human well-being and advancing the field of deformable electronics. Various luminescent materials, such as perovskites and organics, have been integrated with stretchable elastomers to function as the stretchable emissive layers in these intrinsically stretchable LEDs. Stretchable conductors including Ag nanowire based percolating structures and conducting polymers have been utilized as stretchable transparent electrode. Despite this progress, their performances in terms of efficiency and stability remain challenging compared to their structurally stretchable and rigid LED counterparts. This review offers a comprehensive overview of recent advancements in intrinsically stretchable LEDs, focusing on material innovations.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.54-55
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• 2001

Recently, there has been much interests in InGaN/GaN multiple-quantum-well (MQW) structures due to their applicability as optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes [1]. Their ultrafast and physical properties are also of significant interests. Anomalously large acoustic phonon oscillations have been observed using ultrafast lasers in InGaN MQWs [2]. In this study, we have peformed femtosecond pump-probe experiments in the reflection geometry on 5 periods InGaN/GaN MQW LED structure with well width of 20$\AA$ and barrier width of 100$\AA$ at room temperature. (omitted)

• Korean Journal of Medicinal Crop Science
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• v.17 no.1
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• pp.39-45
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• 2009

The effects of red, blue, and far-red light by illumination of light emitting diodes (LEDs) on growth, morphogenesis and eleutheroside contents of in vitro plantlets of Eleutherococcus senticosus were examined. As a control, plantlets were grown under a broad spectrum white fluorescent lamp (16/8 h illumination). The length of plantlets grown under the red/blue LEDs was taller than those under fluorescent lamps. Leaf area, root length and fresh weight of plantlets were highest under blue light compared to other kinds of light sources. Chlorophyll contents in plantlets grown under fluorescent lamps were higher than those in plantlets grown under LED illumination. Production of eleuthroside B and E in plantlets was highest under blue LED. However, production of eleuthroside E1 was highest under fluorescent lamps. These results suggest that plant growth and eleuthroside accumulation can be controlled by wave length of light under LED illumination system.

• Current Optics and Photonics
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• v.6 no.3
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• pp.332-336
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• 2022

Given a cubic space, it is easy to uniformly illuminate the floor with light sources placed on top. However, little has been reported about uniform illumination on walls with the same configuration of light sources. Here we present a luminaire consisting of nine light-emitting diodes (LEDs) with perfect Lambertian distribution, placed on the top as a 3 × 3 rectangular LED array. The distances between LEDs and tilt angles of each individual LED are adjustable and optimized by an annealing algorithm. After optimization, the array produces a rectangular illumination pattern on one wall with a uniformity of about 89%. Analysis shows that the tilt angles of individual LEDs are key parameters for uniform side illumination. In a scenario that is more practical, the tilt angles of all the LEDs are set to be the same, only decreasing the uniformity to 83%.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.171-171
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• 2012

In this study, we fabricated the high-brightness AlGaInP-based red light emitting diodes (LED)s using by direct printing technique and inductive coupled plasma (ICP) reactive ion etching (RIE). In general, surface roughening was fabricated by wet etching process to improve the light extraction efficiency of AlGaInP-based red LED. However, a structure of the surface roughening, which was fabricated by wet etching, was tiled cone-shape after wet etching process due to crystal structure of AlGaInP materials, which was used as top-layer of red LED. This tilted cone-shape of surface roughening can improve the light extraction of LED, but it caused a loss of the light extraction efficiency of LED. So, in this study, we fabricated perfectly cone shaped pattern using direct printing and dry etching process to maximize the light extraction efficiency of LED. Both submicron pattern and micron pattern was formed on the surface of red LED to compare the enhancement effect of light extraction efficiency of LEDs according to the diameter of sapphire patterns.After patterning process using direct printing and ICP-RIE proceeded on the red LED, light output was enhanced up to 10 % than that of red LED with wet etched structure. This enhancement of light extraction of red LED was maintained after packaging process. And as a result of analyze of current-voltage characteristic, there is no electrical degradation of LED.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.46-49
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• 2011

Bi co-doped ZnS:Mn,Bi yellow phosphors for white light emitting diodes were prepared by the conventional solidstate reaction method. The optical and structural properties of ZnS:Mn,Bi phosphors were investigated by x-ray diffraction, scanning electro microscopy and photoluminescence. ZnS:Mn,Bi phosphors showed XRD patterns of hexagonal structure. The photoluminescence of ZnS:Mn,Bi phosphors showed spectra extending from 480 to 700 nm, peaking at 580 nm. The photoluminescence of 580 nm in the ZnS:Mn,Bi phosphors was associated with the 4T1 ${\rightarrow}$ 6A1 transition of the Mn2+ ions. The highest photoluminescent intensity of the phosphors under 405 nm and 450 nm excitation was obtained at Bi concentration of 7mol%. The optimum mixing conditions with epoxy and yellow phosphor for white light emitting diodes were observed in a ratio of epoxy:yellow phosphor of 1:3.5. The CIE chromaticity of the white LED at the 1:3.5 ratio was X = 0.3454 and Y = 0.2449.