• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.189-196
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• 2014

Water dispersible ZnS based nanocrystals: ZnS (blue), ZnS:Cu (green) and ZnS:Mn (yellow-orange) were synthesized by capping the surface of the nanocrystals with a mercaptopropionic acid (MPA) molecule. The MPA capped ZnS based nanocrystal powders were characterized by using XRD, HR-TEM, EDXS, FT-IR, and FT-Raman spectroscopy. The optical properties of the colloidal nanocrystals were also measured by UV/Vis and photoluminescence (PL) spectroscopies in aqueous solvents. The PL spectra showed broad emission peaks at 440 nm (ZnS), 510 nm (ZnS:Cu) and 600 nm (ZnS:Mn), with relative PL efficiencies in the range of 4.38% to 7.20% compared to a reference organic dye. The measured average particle sizes from the HR-TEM images were in the range of 4.5 to 5.0 nm. White light emission was obtained by mixing these three nanocrystals at a molar ratio of 20 (ZnS):1 (ZnS:Cu):2 (ZnS:Mn) in water. The measured color coordinate of the white light was (0.31, 0.34) in the CIE chromaticity diagram, and the color temperature was 5527 K.

• Journal of the Korean institute of surface engineering
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• v.46 no.2
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• pp.93-97
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• 2013

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with co-doping and blue/co-doping emitting layer (EML) structures were fabricated using a host-dopant system. The total thickness of light-emitting layer was 25 nm and the dopant of blue and red was FIrpic and $Bt_2Ir(acac)$ in UGH3, respectively. In case of co-doping structure, applying micro lens array film showed efficiency improvement from the current efficiency 78.5 cd/A and power efficiency 40.4 lm/W to the current efficiency 131.1 cd/A and power efficiency 65 lm/W and blue / co-doping structure showed efficiency improvement from the current efficiency 43.8 cd/A and power efficiency 22 lm/W to the current efficiency 69 cd/A and power efficiency 32 lm/W.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1090-1092
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• 2006

There is provided white light illumination system including a radiation source, a first luminescent material having a peak emission wavelength of about 575 to about 620 nm, a second luminescent material having a peak emission wavelength of about 495 to about 550 nm, which is different from the first luminescent material and a third luminescent material having a peak emission wavelength of about 420 to about 480 nm, which is different from the first and second luminescent materials. The LED may be a UV LED and the luminescent materials may be a blend of three phosphors. A human observer perceives the combination of the blue, green and red phosphor emissions as white light.

• Rapid Communication in Photoscience
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• v.2 no.1
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• pp.34-37
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• 2013

Two novel antenna complexes of $Eu^{III}$ with 1-naphthoic acid (NA) as primary ligand and two aromatic N-donor ligands namely N-hexyl-N-(pyridin-2-yl) pyridin-2-amine (1) and 4-((dipyridin-2-ylamino)methyl)benzoic acid (2) have been synthesized and characterized by various spectroscopic techniques. The room-temperature (298 K) photoluminescence spectrum of $Eu^{III}$ complexes composed of typical line like emissions, assigned to transitions between the first excited state $^5D_0$ to the $^7F_J$ (J = 0-4), resulting in red emission along with the residual emission from the 1-naphthoic acid moiety in the blue region. The determined CIE color coordinate value for the complex 2 is (x = 0.36, y = 0.34), which is in white region.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.196-201
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• 2016

We studied white tandem organic light-emitting diodes using blue and red phosphorescent materials. Optimized white single phosphorescent OLED was fabricated using CBP : FIrpic (12 vol.%, 9 nm) / CBP : $Ir(mphmq)_2acac$ : $Ir(ppy)_3$ (1 vol.%, 1 vol.%, 1 nm) as emitting layer (EML). The single phosphorescent OLED showed maximum current efficiency of 22.5 cd/A, white emission with a Commission Internationale de l'Eclairage (CIE) coordinates of (0.342, 0.37) at $1,000cd/m^2$, and variation of CIE coordinates with ($0.339{\pm}0.008$, $0.371{\pm}0.001$) from 500 to $3,000cd/m^2$. Optimized white tandem phosphorescent OLED was fabricated using CBP : FIrpic (12 vol.%, 7 nm) / CBP : $Ir(mphmq)_2acac$ : $Ir(ppy)_3$ (1 vol.%, 1 vol.%, 3 nm) as EML. The tandem phosphorescent OLED showed maximum current efficiency of 49.2 cd/A, white emission with a CIE coordinates of (0.376, 0.366) at $1,000cd/m^2$, variation of CIE coordinates with ($0.375{\pm}0.004$, $0.367{\pm}0.002$) from 500 to $3,000cd/m^2$. Maximum current efficiency of tandem phosphorescent OLED was more twice as high as single phosphorescent OLED. Our results suggest that tandem phosphorescent OLED was possible to control CIE coordinates and produce excellent color stability.

• Journal of The Korean Astronomical Society
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• v.48 no.2
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• pp.105-112
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• 2015

The symbiotic star V1016 Cygni, a detached binary system consisting of a hot white dwarf and a mass-losing Mira variable, shows very broad emission features at around 6825 Å and 7082 Å, which are Raman scattered O vi λλ 1032, 1038 by atomic hydrogen. In the high resolution spectrum of V1016 Cyg obtained with the Bohyunsan Optical Echelle Spectrograph these broad features exhibit double peak profiles with the red peak stronger than the blue counterpart. However, their profiles differ in such a way that the blue peak of the 7082 feature is relatively weaker than the 6825 counterpart when the two Raman features are normalized to exhibit an equal red peak strength in the Doppler factor space. Assuming that an accretion flow around the white dwarf is responsible for the double peak profiles, we attribute this disparity in the profiles to the local variation of the flux ratio of O vi λλ 1032, 1038 in the accretion flow. A Monte Carlo technique is adopted to provide emissivity maps showing the local emissivity of O vi λ1032 and O vi λ1038 in the vicinity of the white dwarf. We also present a map indicating the differing flux ratios of O vi λλ 1032 and 1038. Our result shows that the flux ratio reaches its maximum of 2 in the emission region responsible for the central trough of the Raman feature and that the flux ratio in the inner red emission region is almost 1. The blue emission region and the outer red emission region exhibit an intermediate ratio around 1.5. We conclude that the disparity in the profiles of the two Raman O vi features strongly implies accretion flow around the white dwarf, which is azimuthally asymmetric.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1429-1432
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• 2007

We fabricated white organic light emitting diodes(WOLED) having two complementary and three primary colors with emission layers of DPVBi / MADN : DCM2-0.5% and DPVBi / $Alq_3$ / MADN : DCM2-1.5%, respectively. WOLED using three primary colors shows broad electroluminescence including green emission peak at 510nm while optical properties of the two complementary WOLED was higher current efficiency of 6.2 cd/A than 4.9 cd/A of three primary color WOLED. The maximum luminescence of WOLED with two complimentary color was $15200cd/m^2$ along with luminous efficiency 6.2cd/A, as achieving stable white color coordinates for both of WOLEDs at (0.33 , 0.33) almost.

• Transactions on Electrical and Electronic Materials
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• v.11 no.3
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• pp.145-148
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• 2010

White organic light emitting devices were fabricated to improve the stability through a structural change using the two peak emission method. The fabricated devices were composed of indium tin oxide (100 nm)/ $\alpha$-NPD (30 nm)/4,40-bis(2,20-diphenylvinyl)-1,10-biphenyl (DPVBi, d: variable)/DPVBi: Rubrene (40 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline(5 nm)/ $Alq_3$(5 nm)/ Al (100 nm). A DPVBi for blue emissions was used as the host material in the emitters. The doping concentration of the Rubrene was fixed at 2.0% (by weight). The white emission with Commission Internationale De L'Eclairage coordinates of (0.3342, 0.3439) occurred at 14 V with a thickness d of 1 nm. It was insensitive to the drive voltage, and the devices had a maximum luminance of $211\;cd/cm^2$. At 19 V, the current density and maximum external quantum efficiency were $173\;mAcm^2$ and 0.478%, respectively.

• Journal of the Korea Society of Computer and Information
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• v.10 no.1 s.33
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• pp.1-6
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• 2005

White light emission is very important for applying electroluminescent device to full display, backlight and illumination light source. In this letter, Multilayer molecular organic white-light-emitting device using thin nim of blue material nitro-DPVT with fluorescent dye Rubrene for an orange emission were fabricated. The basic structure of the fabricated device is a-NPD / nitro-DPVT / nitro- DPVT:Rubrene / BCP/ Alq3. Aluminum is used as the cathode material and ITO was anode material. The white light emission spectrum covers a wide range of the visible region and the Commission Internationale do I'E clairage (C.I.E.) coordinates of the emitted light was ((0.3347, 0.3515) at 14V. The turn voltage is as low as 2.5V and quantum efficiencies are $0.35\%$.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1294-1296
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• 2005

We have fabricated white organic light emitting diodes. To obtain balanced white emission and improve the efficiency of devices, thin electron blocking layer (TEBL) was inserted between the emitting layers. We showed that the effective injection of electrons through the optimization of TEBL (a - NPD) embodied the balance of spectra and had a possibility of getting white emission. In a device with 0.3 nm a-NPD, it had a maximum power efficiency of 3.80 lm/w at 250 $cd/m^2$, a luminance of 1200 $cd/m^2$ at 100 $mA/cm^2$ , and the CIE coordinates were (0.353, 0.357).