• Current Optics and Photonics
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• v.7 no.5
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• pp.496-503
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• 2023

We present a detailed analysis of the light extraction efficiency (LEE) of a core-shell nanorod light emitting diode (LED) using finite-difference time-domain (FDTD) simulations. We found that the LEE has a deep dependence on source positions and polarization directions based on the calculated LEE results for every x and z position inside the core-shell nanorod structure. The LEEs are different for the upper part (pyramid) and the lower part (sidewall) of the core-shell nanorod owing to total internal reflection (TIR) and the generated optical modes in the structure. As a result, the LEE of sidewall is much larger than that of pyramid. The averaged LEE of the core-shell nanorod LED is also investigated with variable p-GaN thickness, n-GaN thickness, and height for the design guidelines for the optimized LEE of core-shell nanorod LEDs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.16-16
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• 2010

GaN-based light-emitting diodes (LEDs) are attracting great interest as candidates for next-generation solid-state lighting, because of their long lifetime, small size, high efficacy, and low energy consumption. However, for general illumination applications, the external quantum efficiency of LEDs, determined by the internal quantum efficiency (IQE) and the light extraction efficiency, must be further increased. The IQE is determined by crystal quality and epitaxial layer structure and high value of IQE more than 70% for blue LEDs have been already reported. However, there is much room for improvement of light extraction efficiency because most of the generated photons from active layer remain inside LEDs by total internal reflection at the interface of semiconductor with air due to the high refractive index difference between LEDs epilayer (for GaN, n=2.5) and air (n=1). The light confining in LEDs will be reabsorbed by the metal electrode or active layer, reducing the efficacy of LEDs. Here, we present the first demonstration of enhanced light extraction by forming a MgO nano-pyramids structure on the surface of vertical-LEDs. The MgO nano-pyramids structure was successfully fabricated at room temperature using conventional electron-beam evaporation without any additional process. The nano-sized pyramids of MgO are formed on the surface during growth due to anisotropic characteristics between (111) and (200) plane of MgO. The ZnO layer with quarter-wavelength in thickness is inserted between GaN and MgO layers to increase the critical angle for total internal reflection, because the refractive index of ZnO (n=1.94) could be matched between GaN (n=2.5) and MgO (n=1.73). The MgO nano-pyramids structure and ZnO refractive-index modulation layer enhanced the light extraction efficiency ofV-LEDs with by 49%, comparing with the V-LEDs with a flat n-GaN surface. The angular-dependent emission intensity shows the enhanced light extraction through the side walls of V-LEDs as well as through the top surface of the n-GaN, because of the increase in critical angle for total internal reflection as well as light scattering at the MgO nano-pyramids surface.

• Journal of Applied Biological Chemistry
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• v.64 no.3
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• pp.197-203
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• 2021

Saponarin is a crucial component of barley sprout, and the production and quantitative analysis are issued to date. In this study, the optimal saponarin extraction conditions were presented on the subject of acetonitrile, ethanol, methanol, and water for the quantitative analysis in barley sprout through the extraction efficiency compared with the solvent concentration and extraction time using the reaction surface methodology. The optimal extraction time and solvent condition for saponarin were 3.9 h and 53.7% of aqueous methanol, respectively. In addition, the effect of LED artificial light on the saponarin production in barley sprouts was evaluated by the light cycle, light quantity, and light quality. The optimal cultivation conditions under artificial light for the growth of barley sprout and saponarin production were most effectively achieved on 220-320 μmol m^-2 s^-1 of the light quantity with 8 h day^-1 of a daylight cycle under 6500K LED combined with red light. Furthermore, blue light was evaluated as the main factor in the biosynthesis of saponarin.

• Journal of IKEEE
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• v.24 no.1
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• pp.140-146
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• 2020

We investigated light extraction film based on polymer dispersed liquid crystal (PDLC) for application in organic light emitting diodes (OLEDs). At least 30 seconds of direct UV irradiation process for curing PDLC film on a bottom-emitting OLEDs was successfully achieved without damage on the intrinsic properties of the OLED. We demonstrated that high haze and transmittance can be tuned simultaneously by controlling the UV curing time. By adding PDLC as an external layer without any additional treatment, the light scattering and extraction is increased. Consequently, a PDLC scattering film with 89.8% and 59.9 of total transmittance and haze respectively, achieved about 16% of light intensity enhancement from integrating sphere measurement.

• Resources Recycling
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• v.26 no.2
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• pp.3-10
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• 2017

Rare earth elements with high purity are demanded for the manufacture of advanced materials. Light rare earth elements are contained in domestic monazite and Ni-MH batteries. In this paper, solvent extraction to separate the light rare earth elements from hydrochloric acid leaching solutions of these resources was discussed. A mixture of cationic and tertiary amine shows synergistic effect on the extraction of LREEs and the extent of pH decrease during extraction is reduced. The effect of solution pH on the extraction and synergism was reviewed. Acquisition of the operation data with mixer-settler on the separation of LREEs by this mixture is necessary to develop a process.

• Journal of Environmental Health Sciences
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• v.24 no.2
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• pp.74-79
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• 1998

This study was conducted to evaluate the surfactant solutions which influence solvent extraction from light hydrocarbon contaminated soils. Nine characteristic compounds were studied: benzene, toluene, ethylbenzene, o-xylene, mxylene, p-xylene, n-propylbenzene, 1,2,4-trimethylbenzene, and n-butylbenzene which were found in gasoline. Adsee-799 and Witbreak DRA-22 showed some extractive capacity for light hydrocarbons from soil. There was no added advantage obtained by using other surfactants in this study. No removal of contaminants from soil was observed when the surfactant concentration was 0.5 percent or below. When the surfactant concentration was 4 percent, the average recovery for some hydrocarbons was 10.8 percent, which was the best obtained at these levels. There was 10 percent surfactant contribution for methanol extraction from soil with the Witbreak DPG-482 and Witbreak DRA-22. This study provided a useful screening technique for procedures that can be used to remediate soils contaminated with light hydrocarbons.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.7
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• pp.446-449
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• 2015

An improvement of light-extraction efficiency of organic light-emitting diodes was studied by using random-textured films (RTF). Device was made in a structure of RTF/glass/ITO/TPD/$Alq_3$/LiF/Al. RTF mold was made by spreading PDMS solution on a sandpaper. By pressing this mold on the glass substrate pre-coated with ZPU material, the RTF was obtained. From this study, there was an improvement of external quantum efficiency by about 30% in the device with the random-textured film (RTF 40) compared to that of the reference one.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.705-708
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• 2014

We demonstrate the blue InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) with an embedded air-gap photonic crystal (PC) which was fabricated by the lateral epitaxial overgrowth of GaN layer on the tungsten (W) nano-masks. The periodic air-gap PC was formed by the chemical reaction of hydrogen with GaN on the W nano-mask. The optical output power of LEDs with an air-gap PC was increased by 26% compared to LEDs without an air-gap PC. The enhanced optical output power was attributed to the improvement in internal quantum efficiency and light extraction efficiency by the air-gap PC embedded in GaN layer.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.211-214
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• 2008

GaN-based light-emitting diodes (LEDs) of a 405 nm wavelength have been fabricated on a sapphire substrate by metal organic chemical vapor deposition (MOCVD). In order to reflect the photons, which are generated in the InGaN active region and emitted to the backside, to the front surface, a reflection layer was deposited onto the back of the substrate. Aluminum was used as the reflection layer and Al was deposited on the sample followed by Ti evaporation for firm adhesion of the reflection layer to the substrate. The light extraction efficiency was enhanced 52 % by adoption of the Ti-Al reflection layer.

• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.122-129
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• 2003

In the case of a AIGalnP/GaP system rectangular parallelepiped high brightness LED which has side walls etched to be slanted off the vertical direction, we have studied the effects of lossy electrodes and material absorption and etching depth and angle of side walls on its light extraction efficiency. If LEDs have no electrodes, in order to obtain an 80％ light extraction efficiency of a TIP (truncated inverted pyramid) LED, the side-etched LEDs should have an etching angle of 22$^{\circ}$~45$^{\circ}$ and an etching depth of 8~17% of a dice height and an absorption coefficient less than 1 $cm^{-1}$ / In case of etching depth of 16~39% of a dice height, we can obtain a 90% light extraction efficiency of a TIP LED. But when LEDs have two electrodes and no absorption loss, in order to obtain an 80％ light extraction efficiency of a TIP LEBs, the side-etched LEDs should have an etching angle of 25$^{\circ}$-45$^{\circ}$ and an etching depth of 30～36% of a dice height. In case of etching depth of 57~71％ of a dice height, we can obtain a 90％ light extraction efficiency of a TIP LED.