• Korean Journal of Materials Research
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• v.16 no.10
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• pp.624-628
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• 2006

In this study, divalent europium-activated $NaCaPO_4$ green phosphor powders were prepared by the chemical synthetic method followed by heat treatment in reduced atmosphere, and the crystal structures, morphologies and photoluminescent properties of the powders were investigated by x-ray powder diffraction, scanning electron microscope and spectrometer for the first time. The effects of Ca/P and Na/Ca mole ratios on the final products were also investigated. The influences of input amount change of europium as the activator on the light emission intensity were studied, and the resulting concentration quenching phenomenon was observed. The optimized synthesis conditions obtained in this study were Ca/P mole ratio 1.2, Na/Ca mole ratio 3.0 and 4 mole%Eu. The peak wavelength was 505 nm for all the samples. The result of excitation spectrum measurement indicated that the excitation efficiency was high for the long-wavelength UV region. It was thus concluded that the samples prepared in this study can be successfully applied for the light-emitting devices such as LED excited with long-wavelength UV light sources.

• Korean Journal of Materials Research
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• v.12 no.7
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• pp.517-521
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• 2002

Europium-activated $Ga_2$$O_3$ phosphor powders were prepared by Pechini method from the mixed aqueous solutions of gallium(III) nitrate, europium(III) nitrate, ethylene glycol and citric acid. The phase formation process and particle shape of the powders obtained were investigated by means of TG/DTA, XRD and SEM. It was found that the powders were amorphous or ${\gamma}$-$Ga_2$$O_3$-like phase up to $500^{\circ}C$ and then transformed into $\beta$- $Ga_2$$O_3$ phase above $600 ^{\circ}C$. The powders calcined below $1000^{\circ}C$ were spherical and nanometer-sized. Photoluminescence spectra measured at room temperature showed that the highest luminescence intensity was obtained for the sample synthesized under the conditions of 2 mol% Eu concentration and heat treatment at $1000^{\circ}C$.

• Applied Chemistry
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• v.15 no.1
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• pp.25-28
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• 2011

A highly sensitive spectrofluorimetric method was developed for the determination of levodopa based on the formation of a ternary complex with Eu³⁺ in the presence of ethylenediaminetetraacetic acid. It was found that this complex manifests intense fluorescence at 591 and 613 nm with excitation at 372 nm and maximum intensity was obtained at 613 nm. Under the optimum conditions, the enhanced fluorescence intensity was proportional to the concentration of levodopa over the range of 3×10^-9-2.5×10^-7 mol L^-1 with limit of detection (LOD) of 4.37×10^-10 mol L^-1. The method offers higher sensitivity and selectivity which could be effectively applied for the determination of levodopa in pharmaceutical and biological samples.

• Journal of the Korean Applied Science and Technology
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• v.32 no.1
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• pp.31-39
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• 2015

The synergistic solvent extraction of rare earth elements such as europium and yttrium has been investigated by the extractant with crown ether as an additive. Macrocyclic ligand as host-guest compounds form more stable complexes with metal ions which have the similar size of the cavity of crown ether. In our previous study[14] founded that the extraction used fatty acid of the various alkyl chain length. Based on the results of the previous experiment, the synergistic separation effect of two metals investigated that the hexanoic acid had was the worst extraction effect which added a crown ether such as 18-crown-6 ether, 15-crown-5 ether, and 12-crown-4 ether. In this study, the concentrations of hexanoic acid have showed the separation effect, and then the concentrations and kind of crown ether are performed for synergistic extraction at the hexanoic acid concentration of the highest separation effect. As a results, the separation rate is the highest value of 1.72 at 0.05 M hexanoic acid, and 0.002M 15-crown-5 ether is the best value in other concentrations and kind of crown ether, it is about twice of using only hexanoic acid. Moreover, the extraction species of two metals has been founded $MLR_3{\cdot}3RH$ form when added the crown ether.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1510-1513
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• 2005

The luminescent properties of $Eu^{3+}$ and $Sm^{3+}$ doped potassium tungstate phosphor were investigated. The $K_{4-3x}(WO_4)_2:Eu_x$, $Sm_y$ phosphor was produced by firing the mixed precursors, followed by re-firing with a flux. The re-firing process provided the clean surface to the particles. The excitation spectra showed that the strong absorption in the region of ultra violet light occurred due to the high europium doping concentration. The incorporation of europium to potassium tungstate was easier, compared to other host materials. The excitation spectra could be controlled by the small addition of samarium. The increase of energy absorption around 405nm was assigned to the $Sm^{3+}$ ions. The comparison between real x-ray diffraction and simulated one revealed that the crystal structure of $K_{4-3x}(WO_4)_2:Eu_x,Sm_y$ phosphor is monoclinic with a space group, C2/c.

• Proceedings of the Optical Society of Korea Conference
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• 2004.07a
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• pp.296-297
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• 2004

시분할 형광 분석법은 발광하는 형광을 통해 시료내의 미량의 물질을 분석 할 수 있는 분석법으로 생화학, 면역학 등 여러 분야에서 응용되고 있으며 새로운 응용 분야에 대한 연구가 활발하게 진행되고 있다. 본 연구에서는 유러피엄(Europium) 화합물을 면역학적 검출기로 사용한 측방유동 시료(lateral flow assay)를 시분할 형광 분석법으로 측정한 결과를 소개한다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.609-612
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• 1999

Organic electroluminescent(EL) devices have received a great deal of attention due to their potential application as full-color displays. They are attractive because of their capability of multicolor emission, ease of fabrication, and operation at a low driving voltage. In this study, single and multiple quantum-well structures consisting of Eu(TTA)$_3$(bpy) complex well layer sandwiched between triphenyldiamine derivative (TPD) layers were fabricated and their photoluminescent electroluminescent characteristics were also investigated. Sharp emission at 616 nm has been observed from the Eu complex in multilayer, single and multiple quantum-well structures. Details on the explanation of electrical properties of these structures will be discussed.

• Journal of the Korean Applied Science and Technology
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• v.18 no.1
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• pp.12-19
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• 2001

Eu(III) exhibits one electron-transfer reduction at $E_{1/2}$ = -0.564 V(vs. Ag/AgCl) and the hypersensitive peak at 615 ㎚ corresponding to $^{5}D_{0}{\rightarrow}^{7}F_{2}$ transition in 0.1 M $LiClO_{4}$ aqueous solution. Upon the addition of 2,6-pyridine dicarboxylic acid(PDA) to the Eu(III) aqueous soultion, the reduction potential shifts negatively and the PDA, and the Eu(III)-PDA complex emits great fluorescence than free-Eu(III) ion at 615 nm. The results are interpreted in term of the electrochemical and spectrofluorometric studies.

• Bulletin of the Korean Chemical Society
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• v.22 no.2
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• pp.199-204
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• 2001

A Cryptate (221) having a short alcohol pendant (2) was metallated with europium(Ⅲ) in anhydrous condition, and its hydrolytic activity for phosphate esters at neutral pH was examined. While the activity for the phosphate diester and monoester is comparable to that of the parent metal complex [1Eu]3+, its hydrolytic activity towards a phosphate triester is significantly suppressed. Potentiometric titration and luminescence spectroscopic studies for the equilibrium behavior of the complex in solution suggest that a dimer formation through the metal hydroxides as well as the pendant alcohol is likely to happen. The low hydrolytic activity for the triester seems to be associated with the dimer formation.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.3055-3060
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• 2012

A simple, rapid and sensitive spectrofluorometric method was developed for the determination of folic acid (FA), based on its quenching effect on the fluorescence intensity of enoxacin (ENX)-europium ($Eu^{3+}$) complex as a fluorescent probe. Fluorometric interaction between ENX-$Eu^{3+}$ complex and FA was studied using UV-visible and fluorescence spectroscopy. The quenched fluorescence intensity at an emission wavelength of 614 nm was proportional to the concentration of FA. Optimum conditions for the determination of FA were investigated. Under optimal conditions, the reduced fluorescence intensity at 614 nm was responded linearly with the concentration of FA. The linearity was maintained in the range of $1.25{\times}10^{-9}$ to $1.50{\times}10^{-7}$ M (R = 0.9986) with the limit of detection ($3S_b/m$) (where $S_b$ is the standard deviation of blank and m is the slop of linear calibration curve) of $6.94{\times}10^{-10}$ M. The relative standard deviation (RSD) for 9 repeated measurements of $1.0{\times}10^{-9}$ M FA was 1.42%. This method was simple, cost effective, and relatively free of interference from coexisting substances. Successful determinations of FA in pharmaceutical formulation and biological samples with the developed method were demonstrated.