• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4321-4326
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• 2011

A new series of heteroleptic cyclometalated iridium(III) complexes has been synthesized and characterized by absorption, emission and cyclic voltammetry studies: $(pqx)_2Ir(acac)$ (1), $(dmpqx)_2Ir(acac)$ (2) and $(dfpqx)_2Ir(acac)$ (3) where pqx=2-phenylquinoxalinate, dmpqx=2-(2,4-dimethoxyphenyl)quinoxalinate, dfpqx=2-(2,4-difluorophenyl) quinoxalinate and acac=acetylacetonate anion. The reaction of excess acetylacetone with ${\mu}$-chloride-bridged dimeric iridium complex, $[(C\^N)_2Ir({\mu}-Cl)]_2$, gives a complex 1 and an unusual hydridoiridium(III) complex, $(pqx)IrH(acac)_2$ (4). The complex 1, 2 and 3 show their emissions in an orangered region (${\lambda}_{PL,max}$ = 583-616 nm), and the emission maxima can be tuned by the change of substituent at phenyl ring of 2-phenylquinoxaline ligand. The phosphorescent line shape indicates that the emissions originate predominantly from $^3MLCT$ states with little admixture of ligand-based $^3({\pi}-{\pi}^*)$ excited states. The structures of complex 3 and 4 are additionally characterized by a single crystal X-ray diffraction method. The complex 3 shows a distorted octahedral geometry around iridium(III) metal ion. A strong trans influence of the phenyl ring is examined. In complex 4, there are two discrete molecules which are mirror images each other at the ratio of 1:1 in an unit cell. We propose that the phosphorescent complex 1, 2 and 3 are possible candidates for the phosphors in OLEDs applications.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.4
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• pp.145-151
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• 2005

Color enhancement of African rubies with dark red was carried out by the heat treatment and the hydrothermal treatment method respectively. The heat treatment method brought about an adverse effect causing the color to be deteriorated. However, the hydrothermal treatment method enhanced its color and clarity. The hydrothermal treatment conditions for color enhancement of them were as follows: solvent: 0.9M $Na_2CO_3-1M\;K_2CO_3$, temperature: $450^{\circ}C$, duration: 48 hrs, filling: $30\%$, pressure: 375 atm. As the results of characteristics for African rubies obtained under these conditions, it was known that the amount of $Cr^{3+},\;Fe^{3+},\;Ti^{4+}$ was reduced after the hydrothermal treatment from the ICP/MS and XRF analyses. Also, it was found that the red color from the colorimeter analyses was getting lighter. These results were consistent with the PL analysis showing that the intensity of the luminescence peak generated by the electron transition of $Cr^{3+}$ ion became lower after the hydrothermal treatment compared with the non-treated rubies.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.319-325
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• 2015

Submicron-sized $CeO_2:Er^{3+}/Yb^{3+}$ upconversion phosphor particles were synthesized by spray pyrolysis, and their luminescent properties were characterized by changing the concentration of $Er^{3+}$ and $Yb^{3+}$. $CeO_2:Er^{3+}/Yb^{3+}$ showed an intense green and red emission due to the $^4S_{3/2}$ or $^2H_{11/2}{\rightarrow}^4I_{15/2}$ and $^4F_{9/2}{\rightarrow}^4I_{15/2}$ transition of $Er^{3+}$ ions, respectively. In terms of the emission intensity, the optimal concentrations of Er and Yb were 1.0 % and 2.0%, respectively, and the concentration quenching was found to occur via the dipole-dipole interaction. Upconversion mechanism was discussed by using the dependency of emission intensities on pumping powers and considering the dominant depletion processes of intermediate energy levels for the red and green emission with changing the $Er^{3+}$ concentration. An energy transfer from $Yb^{3+}$ to $Er^{3+}$ in $CeO_2$ host was mainly involved in ground-state absorption (GSA), and non-radiative relaxation from $^4I_{11/2}$ to $^4I_{13/2}$ of $Er^{3+}$ was accelerated by the $Yb^{3+}$ co-doping. As a result, the $Yb^{3+}$ co-doping led to greatly enhance the upconversion intensity with increasing ratios of the red to green emission. Finally, it is revealed that the upconversion emission is achieved by two photon processes in which the linear decay dominates the depletion of intermediate energy levels for green and red emissions for $CeO_2:Er^{3+}/Yb^{3+}$ phosphor.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.4
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• pp.156-159
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• 2007

The red emission properties of $Mn^{4+}$ doped $SrAl_{12}O_{19}$ prepared by the solid-state reaction was investigated, in order to verify its potential to act as the red emitting phosphor of white LEDs. The emission spectrum exhibits a narrow band between $600{\sim}700 nm $ with four sharp peaks occurring at about 643, 656, 666, 671 nm due to the $^2E\to^4A_2$ transition of $Mn^{4+}$. The excitation spectrum exhibits a broad band between $200{\sim}500 nm$ with three peaks occurring at about 338, 398 and 468 nm, respectively. Moreover, the relative emission intensity of $SrAl_{12}O_{19}:Mn^{4+}$ with or without $CaF_2$ and MgO fluxes measured at excitation source 390 nm. The relative emission intensity of $SrAl_{12}O_{19}:Mn^{4+}$ containing 0.67mol% MgO was approximately 30% higher than that of the base composition sample. Strontium hexa-aluminate measured at room temperature as a function of the substituted Mg concentration. MgO was added to replace part of the $Al_2O_3$. Also, the relative emission intensity of $SrAl_{12}O_{19}:Mn^{4+}$ containing 0.67 mol% MgO and 0.67 mol% $CaF_2$ was approximately about 48% higher than that of the base composition $SrAl_{12}O_{19}:Mn^{4+}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.1
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• pp.15-18
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• 2009

To enhance near UV-visible absorption region and to applied phosphor convert-white LEOs (PC-WLEDs), a red phosphor composed of ${Y_2}{SiO_5}:\;EU^{3+}$, $Bi^{3+}$ compounds was prepared by the conventional solid-state reaction. The photoluminescence (PL) shown that samples were excited by near UV light 395 nm for measurement of PL spectra. Emission spectra of samples have shown red emissions at 612 nm ($^5D_0{\to}^7F_2$). The enhanced near $UV{\sim}$ visible excitation spectrum with a broad band centered at 258 nm and 282 nm originated in the transitions toward the charge transfer state (CTS) due to the $Eu^{3+}-Bi^{3+}-O^{2-}$ interaction. The other excitation band at $350\;nm{\sim}480\;nm$, corresponding to the transitions $^7F_0{\to}^5L_9$ (364 nm), $^7F_0{\to}^5G_3$ (381 nm), $^7F_0{\to}^5L_6$ (395 nm), $^7F_0{\to}^5D_3$, (415 nm) and $^7F_0{\to}^5D_2$ (466 nm), occurred due to enhanced the f-f transition increasing $Bi^{3+}$ and $Eu^{3+}$ ions. The PL intensity increased with increased as concentration of $Bi^{3+}$ and the emission intensity becomes with a maximum at 0.125 mol.

• Korean Journal of Materials Research
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• v.19 no.3
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• pp.163-168
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• 2009

$Eu^{3+}$-doped $Y_2O_3$ red phosphor was synthesized in a flux method using the chemicals $Y_2O_3,\;Eu_2O_3,\;H_3BO_3$ and $BaCl_2{\cdot}2H_2O$. The effect of a flux addition on the preparation of $Y_2O_3:Eu_{3+}$ red phosphor used as a cold cathode fluorescence lamp was investigated. $H_3BO_3$ and $BaCl_2{\cdot}2H_2O$ fluxes were used due to their different melting points. The crystallinity, thermal properties, morphology, and emission characteristics were measured using XRD, TG-DTA, SEM, and a photo-excited spectrometer. Under UV excitation of 254 nm, $Eu_2O_3$ 3.7 mol% doped $Y_2O_3$ exhibited a strong narrow-band red emission, peaking at 612 nm. From this result, the phosphor synthesized by firing $Y_2O_3$ with 3.7 mol% of $Eu_2O_3$, 0.25 mol% of $H_3BO_3$ and 0.5 mol% of $BaCl_2{\cdot}2H_2O$ fluxes at $1400^{\circ}C$ for 2 hours had a larger particle size of $4{\mu}m$ on average compared to the phosphor of the $H_3BO_3$ flux alone. In addition, a phosphor synthesized by the two fluxes together had a rounder corner shape, which led to the maximum emission intensity.

• Journal of Radiation Industry
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• v.4 no.3
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• pp.221-226
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• 2010

Physical detection methods, photostimulated luminescence (PSL), thermoluminescence (TL) and electron spin resonance (ESR) were applied to detect electron beam-irradiated agricultural products, such as red pepper, black pepper, raisin, walnut, beef seasoning and pistachio. The absorbed irradiation doses for representative samples were controled at 0, 1, 3, 5 and 10 kGy. PSL values for non-irradiated samples were <700 counts/60s (lower threshold, $T_1$) except beef seasoning, whereas those of irradiated samples were more than 5,000 photon counts, upper threshold ($T_2$) in black pepper, raisin, and beef seasoning and intermediates values of $T_1-T_2$ in red pepper, walnut, and pistachio. Minerals seperated from the samples for TL measurement showed that non-irradiated samples except pistachio (TL ratio, 0.12) were characterized by no glow curves situated at temperature range of $50{\sim}400^{\circ}C$ with TL ratio (0.01~0.08), while irradiated samples except pistachio at only 1 kGy (TL ratio, 0.08) indicated glow curve at about $150{\sim}250^{\circ}C$ with TL ratio (0.28~3.10). ESR measurements of irradiated samples showed any specific signals to irradiation. The samples of both red pepper and pistachio were produced specific signals derived from cellulose radicals as well as single line signals for black pepper and walnut, and multiple signals derived from crystalline sugar radicals for raisin and beef seasoning. In conclusion, The ESR methods can apply for detection of pistachio exposed to electron beam but PSL and TL are not suitable methods. Furthermore, TL and ESR suggeted that both techniques were more useful detection method than PSL to confirm whether red pepper, walnut and beef seasoning samples have been exposed to electron beam.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.359-359
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• 2012

Trivalent rare-earth ($RE^{3+}=Eu^{3+}\;and\;Tb^{3+}$) ions activated $CaGd_4O_7$ phosphors were synthesized by a sol-gel process. After annealing at $1,500^{\circ}C$, the XRD patterns of the phosphor confirmed their monoclinic structure. The photoluminescence excitation spectra of $Eu^{3+}$ and $Tb^{3+}$ doped $CaGd_4O_7$ phosphor shows the broad-band excitations in the shorter wavelength region due to charge transfer band of completely filled $O^{2-}$ to the partially filled $Eu^{3+}$ ions and f-d transitions of $Tb^{3+}$ ions, respectively. The photoluminescence spectra show that the reddish-orange ions and green emission for $Eu^{3+}$ and $Tb^{3+}$ ions, respectively. Owing to the importance of thermal quenching property in the technological parameters, the temperature-dependent luminescence properties of these phosphors were measured for examing the suitability of their applications in the development of light emitting diodes (LEDs). In addition to those measurements, the cathodoluminescence properties were examined by changing the acceleration voltage and filament current. The calculated chromaticity coordinates of these phosphors were close proximity to those of commercially available phosphors for LED and field emission display devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.420.2-420.2
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• 2016

Various fields have been paid attention to upconversion nanoparticles (UCNPs) because of its unique optical properties. Moreover, to use the UC luminescent techniques through cell images for identified apoptosis/necrosis of cancer cells have been performed. They have been studied for a versatile biomedical application such as a biosensing tool, or delivery of active forms of medicines inside living cells. UCNPs have distinctive characteristics such as photoluminescence, special emission, low background fluorescence signal and good colloidal stability, which have many advantages compared with the organic dyes and quantum dots. UCNPs have not only a great potential for imaging (UC luminescence) but also therapies (photo-thermal therapy, PTT and photo-dynamic therapy, PDT) in cancer diagnostics. Therefore, we report the enhancement of upconversion red emission in NaYF4:Yb3+,Er3+ nanoparticles, synthesized via solid-state method with the thermal decomposition of trifluoroacetate as precursors and organic solvent at a high boiling point. The UCNPs have an emission in the field of near infrared wavelength, cubic shape and nano-size in length. In this study, we will further investigate it for cancer therapy with NIR optical detection onto the solid substrate.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.5
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• pp.1-6
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• 2000

We prepared organic light-emitting-diodes (LEDs) with a squarylium(Sq)-doped aluminum quinoline(Alq3) emission layer by the vapor deposition method. We discussed their electro-luminescence(EL) and electrical properties. The EL from Sq had a peak wavelength of 670nm and a half-width of 30nm. Only the EL from So(purely red) could be observed at the doping concentration of over 15mol%, but the luminance were low (0.21cd/$m^2$, 0.1cd/$m^2$) and EL efficiency was under the $10^{-2}$W. Although Sq molecules seemed to act as trap site in Alq3 molecules, they acted as carrier drafts site at doping concentration of over 5mol%.