• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1133-1137
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• 2005

In this paper, a renovated approach in the fabrication of red organic light-emitting diodes (OLEDs) is described. The hard-to-control doping process required for dopant-based red OLEDs can be avoided due to the novel red fluorophores that are not concentration quenching in solid state. Doping is in general a must for phosphorescence OLEDs because of the triplet-triplet annihilation, a common problem for phosphorophore dopants. However, we have recently found that extraordinary red iridium complex showing relatively short emission lifetime render the non-doped phosphorescence red OLED possible.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.1007-1010
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• 2011

$Ir(dpq/dpqx)_2$(przl-R) complexes were prepared and their electrochemical properties were investigated, where dpq, dpqx and przl-R represent 2,3-diphenylquinoline, 2,3-diphenylquinoxaline and N-phenyl-R-pyrazolonate derivatives, respectively. The iridium complexes containing dpq and dpqx as main ligands were reported to show red phosphorescence, and involvement of a pyrazolonate ancillary ligand in the iridium complexes led to high luminous efficiency for organic light-emitting diodes. In this study, we synthesized red phosphorescent iridium complexes containing a new pyrazolonate ancillary ligand and investigated the HOMOs, LUMOs and resulting electrochemical gaps of $Ir(dpq/dpqx)_2$(przl-R) by cyclic voltammetry. The emission wavelengths of the complexes at 600 - 640 nm were consistent with the gaps of 1.95 - 2.03 eV measured from reduction and oxidation potentials of the complexes.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.461-464
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• 2008

We have developed low voltage driving red phosphorescent organic light-emitting devices using a new electron transport layer. $Ir(piq)_3$ and CBP were used as a phosphorescent dopant and an emission host, respectively. The device exhibits a luminance of $1000\;cd/m^2$ at a voltage of 2.8 V. This high luminance at low voltage results from a high electron conduction behavior of the new electron transport layer.

• Bulletin of the Korean Chemical Society
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• v.32 no.11
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• pp.4075-4078
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• 2011

• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.354-363
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• 2011

Quantum-chemistry study was explored to investigate the electronic structures, absorption and phosphorescence mechanism, as well as electroluminescence (EL) properties of three red-emitting Ir(III) complexes, $(fpmqx)_2Ir$(L) {fpmqx=2-(4-fluorophenyl)-3-methyl-quinoxaline; L=triazolylpyridine (trz) (1); L=picolinate (pic) (2) and L=acetylacetonate (acac) (3)}. The calculated results show that the HOMO distribution for 1 is mainly localized on trz moiety due to its stronger ${\pi}$-electron acceptor ability, and HOMO for 2 and 3 is the combination of Ir d- and phenyl ring ${\pi}$-orbital. The higher phosphorescence yields and differences among 1-3 are investigated in this paper. In addition, the reasons of higher EL efficiency of 2 than 1 and 3 have been rationalized.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.9
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• pp.802-807
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• 2007

We have developed red phosphorescent top emission organic light-emitting diodes with transparent metal cathodes deposited by using thermal evaporation technique. Phosphorescent guest molecule, BtpIr(acac), was doped in host CBP for the red phosphorescent emission, Ca/Ag, Ba/Ag, and Mg/Ag double layers were used as cathode materials of top emission devices, which were composed of glass/Ni/2TNATA(15 nm)/${\alpha}$-NPD(35 nm)/CBP:BtpIr(acac)(40 nm, 10%)/BCP(5 nm)/$Alq_3$(5 nm)/cathodes. The optical transparencies of these metal cathodes strongly depend on underlying Ca, Ba, and Mg layers. These layers also strongly affect the electrical conduction and emission properties of the red phosphorescent top emission devices.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.663-666
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• 2007

High-efficiency red phosphorescent OLEDs employing a novel red emitter and a multifunctional oligofluorene host are reported. With qazIr(acac) as the red phosphorescent dopant, a maximum external quantum efficiency of 19% and maximum power efficiency of 11 lm/W are achieved. In addition, single layer devices using such host and dopant materials have efficiencies up to 13%.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2309-2314
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• 2010

Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo[b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: [$(pqx)_2$Ir(biim)]Cl (1), [$(dmpqx)_2$Ir(biim)]Cl (2), [$(dfpqx)_2$Ir(biim)]Cl (3), [$(btp)_2$Ir(biim)]Cl (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 - 0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from -1.15 to -1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at -1.80 V.

• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.350-356
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• 2014

Recently, Chemical Vapor Deposition (CVD) synthetic diamonds have been introduced to the jewelry gem market, as CVD technology has been making considerable advances. Unfortunately, CVD diamonds are not distinguishable from natural diamonds when using the conventional gemological characterization method. Therefore, we need to develop a new identification method that is non-destructive, fast, and inexpensive. In our study, we employed optical microscopy and spectroscopy techniques, including Fourier transform infra-red (FT-IR), UV-VIS-NIR, photoluminescence (PL), micro Raman, and cathodoluminescent (CL) spectroscopy, to determine the differences between a natural diamond (0.30 cts) and a CVD diamond (0.43 cts). The identification of a CVD diamond was difficult when using standard gemological techniques, UV-VIS-NIR, or micro-Raman spectroscopy. However, a CVD diamond could be identified using a FT-IR by the Type II peaks. In addition, we identified a CVD diamond conclusively with the uneven UV fluorescent local bands, additional satellite PL peaks, longer phosphorescence life time, and uneven streaks in the CL images. Our results suggest that using FT-IR combined with UV fluorescent images, PL, and CL analysis might be an appropriate method for identifying CVD diamonds.

• Bulletin of the Korean Chemical Society
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• v.7 no.3
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• pp.196-200
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• 1986

The solvent change and salt do not affect the fluorescence quantum yield of 1,3-dimethylnaphtho[1,2-e]uracil indicating the considerable energy gap between the lowest singlet $({\pi},\;{\pi}^{\ast})\;and\;(n,\;{\pi}^{\ast})$ states in the compound. The results are consistent with the strong quenching of fluorescence by ethyl iodide. Fluorescence quantum yield is nearly independent of temperature, probably due to the relatively inefficient internal conversion. Unusual spectral difference is observed in isopentane and ethanol at 77K. The temperature dependence of emission in isopentane and in ethanol suggests that the increase of charge transfer character by the conformational change in isopentane leads to the structureless and red-shifted fluorescence, while in ethanol the decrease of the charge transfer character by the hydrogen bonding interaction results in the structured and blue-shifted fluorescence along with phosphorescence at the low temperature. Temperature dependence of emission in poly(methylmethacrylate) matrix indicates that $T_1{\to}S_0$ radiationless decay is an important process responsible for the strong temperature dependence of phosphorescence.