• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.177-182
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• 2010

To synthesize $Gd_2O_3:Eu^{3+}$ phosphor, gadolinium-europium oxalate precursors were prepared from oxalic acid, NaOH or aqueous ammonia via coprecipitation method. The obtained precursors were heat-treated and then characterized by XRD, SEM and PL. The kinds and amounts of coprecipitant (NaOH or aqueous ammonia) were found to affect the powder morphology and properties of gadolinium-europium oxalate precursors. Two crystalline precursors and one amorphous precursor were synthesized. The nanometer-sized amorphous gadolinium-europium oxalate precursor was first prepared using the oxalate coprecipitation technique. The calcined powders obtained from the amorphous precursor were nearly spherical in shape, and a narrow size distribution was obtained. The NaOH coprecipitant was more effective in the preparation of nanometer-sized spherical powders. A thermal decomposition process was conducted for the three kinds of precursors. The photoluminescence property was also measured as a function of europium content, and concentration quenching occurred for samples with europium concentrations of over 10 mol%.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1355-1359
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• 2006

Due to its efficient red emission, $Eu^{3+}$ ion has been doped in various host materials. $GdCa_4B_3O_{10}:Eu^{3+}$ phosphor for red emission has been prepared by solid state reaction. Photoluminescence properties for the phosphor under UV and VUV excitation were investigated. The $GdCa_4B_3O_{10}:Eu^{3+}$ phosphor under both excitation conditions shows typical red emission spectrum centered at 611 nm with several weak peaks due to energy transfer from $^5D_O\;to\;^7F_J(J=1,2,3,4)$ of $Eu^{3+}$ ion. On the other hand, the activator content exhibiting the concentration quenching under UV and VUV irradiation is 10 mole% and 2.5 mole%, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.826-829
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• 2003

Metal/chalcogenide glass semiconductor(CGS) thin film devices were produced in the vacuum evaporator by the methode of vacuum thermal evaporation. We investigated the influence of the correlations of thickness of metal and CGS upon the concentration of Metal in a CGS thin film. It has shown that M/CGS thin film devices were very sensitive to temperature.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.155-158
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• 2003

New porphyrin square (1) was prepared by reaction of porphyrin containing pyridine and Re$(CO)_5Cl$ in THF/toluene solvent. 2-(Methylene15-crown-5)-nicotinoly ester(2) was synthesized by reaction of 2-(Hydroxymethyl-15-crown-5 and nicotinoly chloride in $CH_2Cl_2$. In fluorescence quenching studies luminescence was quenched by addition of the guest(2) into host(l). In the host-guest system we could obtain binding constant (K= $1.13{\times}10^{7}M^{-1}$) at decreasing concentration of (2). But the luminescence was dramatically increased after $Na^{+}$ was added into the host-guest system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.133-136
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• 2003

New porphyrin square (1) was prepared by reaction of porphyrin containing pyridine and $Re(CO)_5Cl$ in THF/toluene solvent. 2-(Methylenel5-crown-5)-nicotinoly ester(2) was synthesized by reaction of 2-(Hydroxymethyl-15-crown-5 and nicotinoly chloride in $CH_2Cl_2$. In fluorescence quenching studies luminescence was quenched by addition of the guest(2) into host(l). In the host-guest system we could obtain binding constant (K=$1.13{\times}10^7M^{-1}$) at decreasing concentration of (2). But the luminescence was dramatically increased after $Na^+$ was added into the host-guest system.

• Corrosion Science and Technology
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• v.8 no.4
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• pp.157-161
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• 2009

The corrosion resistance of reinforcing bar was studied to endure the marine environment during shipment. The red rust on the surface did not damage the adherence in the concrete structures, especially in highly alkaline environment, but made the consumer doubt of the quality. The passivation process by alkalization of the quenching water in the tempcore process failed to endure the long shipping period. The ceramic coating by sol-gel process improved the corrosion resistance without damaging the mechanical properties and adherence between concrete and reinfiorcing bar. Optimal concentration of the coating solution and coating temperature were tested. No additional energy was necessary for the coating process by spraying during cooling process, resulting simplified process and low cost. Salt spray test, cyclic corrosion test and atmospheric test were employed to confirm the resistance. The corrosion rates were presented by rating number and polarization resistance. The coating layer was examined by FIB, XRD and SEM etc.

• Journal of the Korean Ceramic Society
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• v.48 no.3
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• pp.251-256
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• 2011

The luminescence properties of polycrystalline ZnO annealed in reducing ambience ($H_2/N_2$) have been studied. An effective quenching of green luminescence with enhanced UV emission from polycrystalline ZnO is observed for the reduced ZnO. The variations of the UV and green luminescence band upon reduction treatment are investigated as a function of temperature in the range between 20 and 300 K. Upon annealing treatment in reducing ambience, the optical quality of polycrystalline ZnO is improved. The UV to green intensity ratio of sintered ZnO approaches close to zero (~0.05). However, this ratio reaches more than 13 at room temperature for polycrystalline ZnO annealed at $800^{\circ}C$ in reducing ambience. Furthermore, the full width at half maximum (FWHM) of the UV band of polycrystalline ZnO is reduced compared to unannealed polycrystalline ZnO. Electron paramagnetic resonance (EPR) measurements clearly show that there is no direct correlation between the green luminescence and oxygen vacancy concentration for reduced polycrystalline ZnO.

• Bulletin of the Korean Chemical Society
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• v.25 no.6
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• pp.869-872
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• 2004

Newly synthesized 8-hydroxyquinoline based benzothiazole derivative 2 showed a distinctive $Hg^{2+}$-selectivity over other transition metal ions in aqueous solution. The fluorescence emission at 455 nm of 2 was completely quenched upon interaction with $Hg^{2+}$ ions in dioxane-$H_2O$ system (9 : 1, v/v). The selectivity was decreased in the order of $Hg^{2+}\;>>\;Cu^{2+}\;>\;Cd^{2+}\;>\;Pb^{2+}\;{\thickapprox}\;Zn^{2+}\;{\thickapprox}\;Ni^{2+},\;and\;Hg^{2+}$ concentration dependent fluorescence quenching profile was observed in the presence of common interfering metal ions as background. The fluorescence behavior of 2 suggests that the prepared compound could be used as a fluorescent signaling subunit for the construction of new $Hg^{2+}$-sensitive ON-OFF type supramolecular switching systems.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.801-806
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• 1998

$Eu^{3+}$ -doped $Y_2$$O_3$ phosphors has been prepared by a polymerized complex method and investigated their powder and luminescence properties. They were compared with phosphors prepared by a solid state reac-thion method. The phosphors synthesized have been characterized by X-ray diffraction low-voltage lu-minescent emission spectroscopy etc. Under low-voltage electron excitation $Eu^{3+}$-doped $Y_2$$O_3$ exhibited a strong narrow-band red emission peaking at 612nm. On the other hand the critical value for concentration quenching of sample prepared by the polymerized complex method fired at $1400^{\circ}C$ is x=0.05 for $(Y_{1-x}Eu_x__2O_3$ The emission intensity of phosphors prepared by the polymerized complex method was higher than that of phosphors prepared by the solid state reaction method.

• Journal of the Korean Ceramic Society
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• v.52 no.2
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• pp.146-149
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• 2015

Silicate glasses with different $Nd_2O_3$ concentrations were prepared through conventional melt-quenching methods while PbS quantum dots (QDs) were precipitated through heat treatment. The peak wavelengths of absorption and the photoluminescence of PbS QDs shifted to the short-wavelength side as the concentration of $Nd_2O_3$ increased. The electron energy loss spectroscopy (EELS) indicated that $Nd^{3+}$ ions were preferentially distributed inside the PbS QDs instead of the glass matrix. In addition, there was no significant change in the lifetimes of the $Nd^{3+}:^4F_{3/2}$ fluorescence between the as-prepared glass ($607{\mu}s$) and the heat-treated glass($576{\mu}s$). $Nd^{3+}$ ions were surrounded by oxygen instead of sulfur and the Nd-O clusters probably acted as nucleating centers for the formation of PbS QDs inside the glasses.