• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.478-481
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• 2006

Energy is vital to global prosperity, yet dependence on fossil fuels as our primary energy source contributes to global climate change environmental degradation, and health problems. Hydrogen $(H_2)$ offers tremendous potential as a clean renewable energy currency. Hydrogen has the highest gravimetric energy density of any known fuel and is compatible with electrochemical and combustion processes for energy conversion without producing carbon-based emission that contribute to environmental pollution and climate change. Numerous methodologies have been developed for effective hydrogen production. Among them, the biological hydrogen production has gained attention, because hydrogen can be produced by cellular metabolismunder the presence of water and sunlight. The green alga Chlamydomonas reinhardtii is capable of sustained $H_2$ photoproduction when grown under sulfur deprived condition. Under sulfur deprived conditions, PSII and photosynthetic $O_2$ evolution are inactivated, resulting in shift from aerobic to anaerobic condition in the culture. After anaerobiosis, sulfur deprived algal cells induce a reversible hydrogenase and start to evolve $H_2$ gas in the light. According to above principle, we investigated the effect of induction parameters such as cell age, cell density. light intensity, and sulfate concentration under sulfur deprived condition We also developed continuous hydrogen production system by sulfate re-addition under sulfur deprived condition.

• Journal of Institute of Convergence Technology
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• v.4 no.1
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• pp.21-27
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• 2014

White LEDs (light-emitting diodes) are promising new-generation light sources which can replace conventional lamps due to their high reliability, low energy consumption and eco-friendly effects. This paper briefly reviews recent progress of oxy/nitride host phosphor and quantum dot materials with broad excitation band characteristics for phosphor-converted white LEDs. Among oxy/nitride host materials, $M_2Si_5N_8:Eu^{2+}$, $MAlSiN_3:Eu^{2+}$ M-SiON(M=Ca, Sr, Ba), ${\alpha}/{\beta}-SiAlON:Eu^{2+}$ are excellent phosphors for white LED using blue-emitting chip. They have very broad excitation bands in the range of 440-460 nm and exhibit emission from green to red. In this paper, In this review we focus on recent developments in the crystal structure, luminescence and applications of the oxy/nitride phosphors for white LEDs. In addition, the application prospects and current trends of research and development of quantum dot phosphors are also discussed.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.861-866
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• 2010

Tetrapod-shaped ZnO crystals were synthesized through a simple oxidation of metallic Zn powder in air without the presence of any catalysts or substrates. X-ray diffraction data revealed that the ZnO crystals had wurtzite structure. It is supposed that the growth of the tetrapod proceeded in a vapor-solid growth mechanism. As the amount of the source powder increased, the size of the tetrapod decreased. The tip morphology of the tetrapod changed from a needle-like shape to a spherical shape with the oxidation time. ZnO crystals with rod shape were fabricated via the oxidation of Zn and Sn mixture. Sn played an important role in the formation of ZnO crystals with different morphology by affecting the growth mode of ZnO crystals. The cathodoluminescent properties were measured for the samples. The strongest green emission was observed for the rod-shaped ZnO crystals, suggesting that the crystals had the high density of oxygen vacancies.

• Journal of the Semiconductor & Display Technology
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• v.17 no.4
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• pp.37-41
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• 2018

$Y_3A_{l5}O_{12}:Ce^{3+},Pr^{3+}$ single crystal phosphor was prepared by floating zone method. single crystal was confirmed to have a Ia-3d (230) space group of cubic structure and showed regular morphology. The optical properties, single crystal exhibited a emission band from green, yellow wide wavelength and 610nm, 640nm red wavelength vicinity. The luminance maintenance rate was decreased by phonon with increasing temperature, but high luminance is maintained more than powder phosphor. In addition, $Y_3A_{l5}O_{12}:Ce^{3+},Pr^{3+}$ single crystal phosphor was applied to a high power blue laser diode, we implemented high power white laser lightings. and it was confirmed that thermal properties over time, due to the effective heat transfer of complete crystal structure. We confirmed that excellent radiant heat properties than powder phosphor was applied to a high power white laser diode.

• Journal of the Semiconductor & Display Technology
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• v.16 no.4
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• pp.11-15
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• 2017

Red phosphors, $Sr_2Si_5N_8:Eu^{2+}$, were synthesized as a single-phase crystal structure by optimizing carbon and $Eu^{2+}$ contents in a carbothermal reduction nitridation method. With increasing $Eu^{2+}$ contents, the photoluminescence spectra were red-shifted from 600 nm peak for 1 mol% for to 700 nm for 7 mol%. It was suggested that this red shift is attributed to the energy transfer from one low-energy sited $Eu^{2+}$ (1) to other high-energy sited $Eu^{2+}$ (2). Finally, the best red sample (620 nm emission peak and 80 nm half width for 3 mole% of $Eu^{2+}$) was packaged on a Blue LED together with two additional green and yellow phosphors, the fabricated White LED showed a high color-rendering index of 90 and white color coordinates of x= 0.321 and y = 0.305.

• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1364-1371
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• 2018

An extensive investigation of photon interaction properties has been made for $Zn_xTe_{100-x}$ alloys (where x = 5, 20, 30, 40, 50) to explore its possible use in sensing and shielding gamma radiations. The results show better and stable response of ZnTe alloys for various photon interaction properties over the wide energy range, with an additional benefit of ease in fabrication due to lower melting points of Zn and Te. Mass attenuation coefficient values show strong dependence on photon energy as well as composition. Effective atomic number has maximum value for $Zn_5Te_{95}$ and lowest for $Zn_{50}Te_{50}$ in the entire energy region. The alloy sample with maximum $Z_{eff}$ shows minimal value of $N_e$ and vice versa. Mean free path follows inverse trend as observed for mass attenuation coefficient. The exposure and energy absorption buildup factors depend upon photon energy, penetration thickness and composition (effective atomic number) of $Zn_xTe_{100-x}$ alloys. It finds its application for sensing and shielding from highly energetic and highly penetrating photons at sites where radioactive materials were used and visibility of material is not a big constraint. Further, energy down conversion property of ZnTe alloys with subsequent emission in green band suggests its potential use in sensing gamma photons.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.1
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• pp.93-97
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• 2022

We report highly efficient quantum dot light-emitting diodes (QLEDs) with TiO₂ nanoparticles (NPs) as an alternative electron transport layer (ETL) and poly (methyl methacrylate) (PMMA) as an insulating layer. TiO₂ NPs were applied as ETLs of inverted structured QLEDs and the effect of the addition of PMMA between ETL and emission layer (EML) on device characteristics was studied in detail. A thin PMMA layer supported to make the charge balance in the EML of QLEDs due to its insulating property, which limits electron injection effectively. Green QLEDs with a PMMA layer produced the maximum luminance of 112,488 cd/m² and a current efficiency of 25.92 cd/A. We expect the extended application of TiO₂ NPs as the electron transport layer in inverted structured QLEDs device in the near future.

• The Journal of Industrial Distribution & Business
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• v.13 no.10
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• pp.31-39
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• 2022

Purpose: Smart city has been observed to benefit most urban areas in different nations. Despite its advantages in the promotion of environmental sustainability and improving business competency in the current context, various literature review papers should be introduced to analyze its drawbacks. The present research aims to provide valuable suggestions for sustainable smart cities development. Research design, data and methodology: Using the qualitative content analysis (QCA), the current author could understand the target audience's motivations and habits by gathering data. This implies that the author may predict the kinds of future initiatives. As a result, the current researcher could ensure developed pertinent research questions and a well-planned method for analyzing the replies. Results: The implementation of green city development suggests encouraging the greening of public spaces and reducing heat from the atmosphere caused by the emission of gases from vehicles and companies. Smart cities are offering a new industrial paradigm that is based on the convergence of information technology. Conclusions: The projection illustrates that most people are migrating to the cities, which calls for an immediate transformation to overcome the immense pressure of making the city accessible, sustainable, prosperous, and safer. Therefore, implementing smart cities within the current world promotes efficiency and increases business sustainability.

• New & Renewable Energy
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• v.19 no.2
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• pp.13-22
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• 2023

With the increased interest in renewable energy, various hydrogen production technologies have been developed. Hydrogen production can be classified into green, blue, gray, and pink hydrogen depending on the production method; each method has different technical performance, costs, and CO₂ emission characteristics. Hence, selecting the technology priorities that meet the company strategy is essential to develop technologically and economically feasible projects and achieve the national carbon neutrality targets. In addition, in early development technologies, analyzing the technology investment priorities based on the company's strategy and establishing investment decisions such as budget and human resources allocation is important. This study proposes a method of selecting priorities for various hydrogen production technologies as a specific implementation plan to achieve the national carbon neutrality goal. In particular, we analyze key performance indicators for technology, economic feasibility, and environmental performance by various candidate technologies and suggest ways to score them. As a result of the analysis using the aforementioned method, the priority of steam methane reforming (SMR) technology combined with carbon capture & storage (CCS) was established to be high in terms of achieving the national carbon neutrality goal.

• Journal of Ceramic Processing Research
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• v.18 no.11
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• pp.810-814
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• 2017

Proton exchange membrane fuel cells (PEMFCs) are some of the most efficient electrochemical energy sources for transportation applications because of their clean, green, and high efficiency characteristics. The optimization of catalyst layer morphology is considered a feasible approach to achieve high performance of PEMFC membrane electrode assembly (MEA). In this work, we studied the effect of the solvent on the catalyst layer of PEMFC MEAs fabricated using the electrostatic spray deposition method. The catalyst ink comprised of Pt/C, a Nafion ionomer, and a solvent. Two types of solvent were used: isopropyl alcohol (IPA) and dimethylformamide (DMF). Compared with the catalyst layer prepared using IPA-based ink, the catalyst layer prepared with DMF-based ink had a dense structure because the DMF dispersed the Pt/C-Nafion agglomerates smaller and more homogeneously. The size distribution of the agglomerates in catalyst ink was confirmed through Dynamic Light Scattering (DLS) and the microstructure of the catalyst layer was compared using field emission scanning electron microscopy (FE-SEM). In addition, the electrochemical investigation was performed to evaluate the solvent effect on the fuel cell performance. The catalyst layer prepared with DMF-based ink significantly enhanced the cell performance (1.2 A cm-2 at 0.5 V) compared with that fabricated using IPA-based ink (0.5 A cm-2 at 0.5 V) due to the better dispersion and uniform agglomeration on the catalyst layer.