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Your search keyword '"Jhun, Chul-Gyu"' showing total 176 results
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176 results on '"Jhun, Chul-Gyu"'

20. Spectroscopic study of white organic light-emitting devices with various thicknesses of emissive layer.

Author

Young Kim, Woo, Kim, You-Hyun, Jhun, Chul-Gyu, Wood, R., Mascher, P., and Moon, C.-B.

Subjects
ORGANIC light emitting diodes, OPTICAL properties, CURRENT density (Electromagnetism), EXPONENTIAL functions, ELECTRIC conductivity, POTENTIAL barrier, ELECTRODES, GAUSSIAN distribution
Abstract

White light-emitting devices based on a donor-acceptor structure were fabricated in order to investigate the dependence of the optical properties of white light emission on the thickness variance (15, 20, 25, and 30 nm) of the emissive layer. The emissive layer has a donor-acceptor system with the host 4,4′,4′′-tris(carbasol-l-nyl)triphenylamine molecule doped with 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) and 5,6,11,12-tetraphenylnaphtacene (Rubrene) molecules for blue and yellowish-green light activators, respectively. The characteristics of current density were analyzed by using a power function of applied field, J=σlEl+1 and the characteristic exponential function, J=J0(e(V-Vd)/V0-1). Through spectroscopic analysis, we obtained three physical quantities governing the device performance: 1) an effective conductivity, 2) a threshold potential, and 3) a characteristic potential barrier, which are associated with the trap-charge limited concentration in the bulk layer, the energy gap of the organic materials, and the barrier energy at the contact of electrodes, respectively. The electroluminescent spectra were studied quantitatively using a multi-peak fit with a Gaussian distribution for each electromagnetic transition. By this approach, we deduced the energy levels of the BCzVBi and Rubrene molecules that give leading information on the light emission mechanism and the energy transfer in the host-dopant system. [ABSTRACT FROM AUTHOR]

Published
2012
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21. Dual mode operation of bistable chiral splay nematic liquid crystal cell using horizontal switching for dynamic operation.

Author

Lee, Seong Ryong, Lee, Joong Ha, Jhun, Chul Gyu, Kwon, Soon-Bum, Yoon, Tae-Hoon, and Kim, Jae Chang

Subjects
LIQUID crystal displays, OPTICAL bistability, ELECTRIC fields, SUBSTRATES (Materials science), ELECTRODES
Abstract

We propose a dual mode liquid crystal display (LCD), which can realize dynamic and memory operating LCD modes in a display panel. Horizontal switching and bistable chiral splay nematic LCD modes are used for the dynamic and memory operations, respectively. As the horizontal switching is applied to the dynamic operation, it is possible to use the same LC texture of splay for realizing dark states of both the dynamic and memory operations. Because, for each operation, pixel division is not required in the proposed dual mode LCD, there is no decrease in aperture ratio and resolution. In order to obtain superior display performance for both operations, a wideband half-wave configuration is employed to the proposed dual mode LCD. Due to the wideband configuration, very low light leakages at the dark state and good dispersion characteristics for the entire visible range are obtained. As a result, the proposed dual mode LCD shows a high contrast ratio of over 100:1 for both the dynamic and memory operations. [ABSTRACT FROM AUTHOR]

Published
2009
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23. Alignment of liquid crystal on a polyimide surface exposed to an Ar ion beam

Author

Gwag, Jin Seog, Jhun, Chul Gyu, Kim, Jae Chang, Yoon, Tae-Hoon, Lee, Gi-Dong, and Cho, Seong Jin

Subjects
Argon -- Properties, Argon -- Research, Polyimides -- Properties, Polyimides -- Research, Liquid crystals -- Properties, Liquid crystals -- Research, Physics
Abstract

Properties of nematic liquid crystals aligned on polyimide surfaces exposed to a low-energy Ar ion beam are investigated. The study revealed that there are few ions or radicals induced by broken bonds on polyimide surfaces bombarded with Ar ion beams.

Published
2004

28. Simple method for measuring the high pretilt angle of nematic liquid crystals.

Author

Gwag, Jin Seog, Lee, Seo Hern, Park, Kyoung-Ho, Park, Won Sang, Han, Kwan-Young, Jhun, Chul Gyu, Yoon, Tae-Hoon, Kim, Jae Chang, Song, Dong-mee, and Shin, Dong-myung

Subjects
LIQUID crystals, POLARIZERS (Light)
Abstract

Pretilt angle measurable by using the conventional crystal rotation method is limited to about 0°-20° and 700-90°. We propose a method by which we can measure the pretilt angle by using the crystal rotation method even if the pretilt angle is between 20° and 70°. In this method, the determination of a pretilt angle is achieved by finding the rotation angles where transmittances are maximum and minimum in the periodic transmittance characteristics obtained with the variation of rotation angle. [ABSTRACT FROM AUTHOR]

Published
2003
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