• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.3
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• pp.221-226
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• 2013

The water soluble quantum dots (QDs) are synthesized by the phase transfer and silica coating reaction. The photoluminescence intensity of silica-coated QDs are mainly affected by the amount of phase transfer agent, SDS (sodium dodecyl sulfate), and the maximum value is obtained at the cmc (critical micell concentration) concentration of SDS in the phase transfer reaction. Based on fluorescence spectra and field emission transmission electron microscope (FETEM), the energy transfer rate by forster resonance energy transfer (FRET) is increasing with the thickness of the silica shell coated on CdSe/ZnS QDs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.413-416
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• 2004

In this study, zinc oxide(ZnO) having large misfit(18.2%) with sapphire was tried to be grown on very thin nitride buffer layers. For the creation of various kinds of nitride buffer layer, sapphire surface was modified by an irradiation of nitrogen ion beam with low energy generated from stationary plasma thruster(SPT) at room temperature. After the irradiation of ion beam, Al-N and Al-O-N bonding was identified to be formed as nitride buffet layers. Surface morphology was measured by AFM and then ZnO growth was followed by pulsed laser deposition(PLD). Their properties are analyzed by XRD, AFM, TEM, and PL. We observed that surface morphology was improved and deep level emission related to defects was almost vanished in PL spectra from the ZnO grown on nitride buffer layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.6
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• pp.501-505
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• 2009

$TiO_2$ nano-particle paste was prepared by ethyl cellulose, $\alpha$-terpineol and bis(2-ethylhexyl) phthalate (dioxcyl phthalate) for dye-sensitized solar cells (DSSCs). Dispersion and absorbance of $TiO_2$ photoanode films was controlled by adding different amount of ethyl cellulose and $\alpha$-terpineol. The morphology of prepared $TiO_2$ films was studied by field emission scanning electron microscopy (FE-SEM) and the optical properties of $TiO_2$ films were measured by UV/vis spectra. Photovoltaic-current density was observed to determine the electrochemical response of DSSCs. Energy conversion efficiency was obtained about 7.1% at ethyl cellulose and $\alpha$-terpineol at optimal mixed ratio (as ethyl cellulose: 0.1 g; $\alpha$-terpineol: 1.5 ml) under illumination with AM 1.5($100\;Wcm^{-2}$) simulated sunlight.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.7
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• pp.550-553
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• 2010

The enhancement of quantum efficiency using a surface modified Ag anode in top-emitting organic light emitting diodes (TEOLEDs) is reported. The operation voltage at the current density of $1\;mA/cm^2$ of TEOLEDs decreased from 9.3 V to 4.3 V as the surface of anode coated with $CuO_x$ layer. The work function of these structures were quantitatively determined using synchrotron radiation photoemission spectroscopy. Secondary electron emission spectra revealed that the work function of the Ag/$CuO_x$ structure is higher by 0.6 eV than that of Ag. Thus, the $CuO_x$ structure acts as a role in reducing the hole injection barrier by about 0.6 eV, resulting in a decrease of the turn-on voltage of top-emitting light emitting diodes.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.338-342
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• 2020

Tin oxide (SnO₂) nanocrystals are synthesized by a thermal evaporation method using a mixture of SnO₂ and Mg powders. The synthesis process is performed in air at atmospheric pressure, which makes the process very simple. Nanocrystals with a belt shape start to form at 900 ℃ lower than the melting point of SnO₂. As the synthesis temperature increases to 1,100 ℃, the quantity of nanocrystals increases. The size of the nanocrystals did not change with increasing temperature. When SnO₂ powder without Mg powder is used as the source material, no nanocrystals are synthesized even at 1,100 ℃, indicating that Mg plays an important role in the formation of the SnO₂ nanocrystals at temperatures as low as 900 ℃. X-ray diffraction analysis shows that the SnO₂ nanocrystals have a rutile crystal structure. The belt-shaped SnO₂ nanocrystals have a width of 300~800 nm, a thickness of 50 nm, and a length of several tens of micrometers. A strong blue emission peak centered at 410 nm is observed in the cathodoluminescence spectra of the belt-shaped SnO₂ nanocrystals.

• Applied Chemistry for Engineering
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• v.16 no.6
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• pp.755-759
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• 2005

This study was based on organic electroluminescence display. Especially, DPAVBi, AVBi and DPVBi for the emitting materials were synthesized by Wittig, Wittig-Horner reaction. This reaction was conducted between phosphorous ylide and 4-(diphenylamino)benzaldehyde, 9-anthraldehyde and benzophenone. The structural property of reaction products were analyzed by FT-IR, $^1H-NMR$ spectroscopy and thermal stability, reactivity and PL property were analyzed by melting point, yield and emission spectrum, respectvely. The photoluminescence spectra of a pure DPAVBi, AVBi and DPVBi were observed at approximately 445nm, 484nm and 450nm, respectively. In this study, it was known that DPAVBi, AVBi, DPVBi had a different reaction properties according to stability of ${\alpha}$-position carbonyl group of the aldehyde, ketone.

• Journal of the Korean Magnetic Resonance Society
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• v.9 no.2
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• pp.103-109
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• 2005

New PVC plasticizer, 2,2,4-trimethyl-1,3-pentanediol-1-butyrate-3-isobutyrate was synthesized via simple esterification with butyric acid and Texanol(a trademark of Eastman Chemicals), the mixture of 2,2,4-trimethyl-1,3-pentanediol-3-isobutyrate and 2,2,4-trimethyl-1,3-pentanediol-1-isobutyrate. The analysis of $^1H-1D,\;^{13}C-1D$ NMR and HMBC spectra identified internal-ester-transfer of 2,2,4-trimethyl-1,3-pentanediol-1-isobutyrate during the reaction. 2,2,4-trimethyl-1,3-pentanediol-1-butyrate-3-isobutyrate gave better properties in PVC than 2,2,4-trimethyl-1,3-pentanediol diisobutyrate(TXIB, a trademark of Eastman Chemicals) such as lower viscosity, higher tensile strength and better elongation. In particular, remarkably reduced migration compared with TXIB suggested a reduced emission of VOC(volatile organic compound) from PVC.

• Journal of Magnetics
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• v.16 no.1
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• pp.27-30
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• 2011

Nano-sized manganese ferrite powders and films, $MnFe_2O_4$, were fabricated by the sol-gel method, and the effects of annealing temperature on the crystallographic and magnetic properties were studied by using X-ray diffractometry, field emission scanning electron microscopy, M$\"{o}$ssbauer spectroscopy, and vibrating sample magnetometry. X-ray diffraction spectroscopy of powder samples annealed above 523 K indicated the presence of spinel structure, and the film samples annealed above 773 K also had spinel structure. The particle size increased with the annealing temperature. For the powder samples, the Mossbauer spectra annealed above 573 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of $Fe^{3+}$ ions. Using the M$\"{o}$ssbauer subspectrum area ratio the cation distribution could be written as ($Mn_{0.52}Fe_{0.48}$) $[Mn_{0.48}Fe_{1.52}]$ $O_4$. However the spectrum annealed at 523 K only showed as a doublet due to a superparamagnetic phase. As the annealing temperature was increased, the saturation magnetization and the corecivity of the powder samples increased, as did the coercivity of film samples.

• Journal of the Korean Wood Science and Technology
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• v.47 no.2
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• pp.200-209
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• 2019

To improve the water resistance of melamine-urea-formaldehyde (MUF) resins, different levels of blocked polymeric 4,4 diphenyl methane diisocyanate (B-pMDI) were blended with MUF resins to prepare B-pMDI/MUF hybrid adhesives, and their adhesion performances were evaluated for the surface lamination of fancy veneer on plywood. FT-IR spectra showed that the de-blocked -NCO groups reacted with the -OH of hydroxymethyl groups of the MUF resins to form urethane bonds at 2% B-pMDI/MUF, which was detected before and after their hydrolysis. The mass loss after the hydrolysis consistently decreased as the B-pMDI level increased, indicating an improvement in the water resistance. As the B-pMDI level increased, the activation energy of hybrid adhesives decreased, which improved the reactivity of the hybrid adhesives. Additionally, the water resistance improvement of the hybrid adhesives increased the tensile shear strength of the surface laminated plywood in semi-water proof and water-proof by 23 % and 8 %, respectively, at 2% B-pMDI level. This was likely due to the urethane linkages in the hybrid adhesives. However, the formaldehyde emission from plywood panels bonded with the hybrid adhesives increased in the dry state, indicating incomplete curing of the hybrid adhesives.

• 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.