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Advanced Materials 12/2008; 21(7):771 - 775. · 13.88 Impact Factor
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ABSTRACT: We studied the polarized laser emission from an anisotropic one-dimensional (1D) birefringent photonic crystal (PC) laser. An active medium layer, which consisted of an epoxy resin doped with fluorescent dye, was sandwiched between two anisotropic 1D PC films. It was shown that efficient laser emissions were generated by optical pumping at relatively low lasing thresholds. The wavelengths of the emitted lasers were 611 and 618 nm, which correspond to the two split eigenmodes at the low-energy band edges that are due to the anisotropy of the PCs. We also demonstrated that the polarization of the lasing emission can be controlled by adjusting the birefringence of the anisotropic PCs.
Journal of Applied Physics 02/2008; 103(3):033103-033103-5. · 2.17 Impact Factor
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Jin Ho Park,
Seung Seok Oh,
Sun Woong Kim,
Eun Ha Choi,
Byoung Hee Hong, Yoon Ho Seo,
Guang Sup Cho,
Byoungchoo Park,
Jongsun Lim,
Sung Cheol Yoon,
Changjin Lee
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ABSTRACT: The authors report on a highly efficient phosphorescent organic light-emitting device (PHOLED) achieved by introducing nanoscale double interfacial layers, made by ultrathin surfactant and low work-function metal layers. It is shown that double interfacial layers play multiple roles in the enhancement of device performance: increasing electron injection, hole blocking, and reducing surface roughness of electroluminescent layer. With double interfacial layers, a PHOLED has shown efficiency as high as ∼ 60 cd/A with a current density of 1.6 mA/cm2 and a luminance of 1000 cd/m2 at 6.5 V, which is higher than that of a control device with a single CsF interfacial layer.
Applied Physics Letters 04/2007; 90(15):153508-153508-3. · 3.84 Impact Factor
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Sun Woong Kim,
Jin Ho Park,
Seung Seok Oh,
Doo Youp Kim,
Eun Ha Choi,
Guang Sup Cho, Yoon Ho Seo,
Seung Oun Kang,
Byoungchoo Park,
Yuki Saito,
Nobuhiro Watanabe,
Hideo Takezoe,
Junji Watanabe
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ABSTRACT: The authors studied the highly efficient green electrophosphorescent light-emission from single-layered organic light-emitting devices made by a simple wet process with a composite solution. The solution was prepared by predissolving organic charge transport, host compounds with green phosphorescent guest iridium complex, and a copolymer of oxadiazole units. The fabricated devices show excellent performances, i.e., operation at relatively low voltages, resulting in a high peak current efficiency (ηc) of 48 cd/A and power efficiency (ηp) of 45 lm/W at a current density of 0.02 mA/cm2. Even at 1000 cd/m2 (2 mA/cm2), high ηc of 50 cd/A and ηp of 22 lm/W were obtained.
Applied Physics Letters 11/2006; 89(21):213511-213511-3. · 3.84 Impact Factor
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Youn Chan Yim,
Jin Ho Park,
Sun Woong Kim,
Eun Ha Choi,
Guang Sup Cho, Yoon Ho Seo,
Seung Oun Kang,
Byoungchoo Park,
Sang Hee Cho,
In Tae Kim,
S. H. Han,
Jongsun Lim,
Hideo Takezoe
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ABSTRACT: The authors studied the effect of thermal and electrical annealing on light emission of fluorescent one-layered organic light-emitting devices (OLEDs) doped with organic salts. From the annealed OLEDs, we clearly observed homogeneous and enhanced electroluminescent (EL) emission over the whole active area with fast responses. Moreover, improved efficiency was also observed from annealed phosphorescent OLEDs. These improved EL characteristics indicate that simultaneous annealing can induce proper adsorption of charged salt ions at the electrode surfaces, leading to enhanced electroluminescence of one-layered OLEDs due to increased and balanced injection of carriers.
Applied Physics Letters 10/2006; · 3.84 Impact Factor
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Jongsun Lim,
Seung Seok Oh,
Doo Youp Kim,
Sang Hee Cho,
In Tae Kim,
S H Han,
Hideo Takezoe,
Eun Ha Choi,
Guang Sup Cho, Yoon Ho Seo,
Seung Oun Kang,
Byoungchoo Park
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ABSTRACT: We studied microcavity organic light-emitting devices with a microlens system. A microcavity for organic light-emitting devices (OLED) was fabricated by stacks of SiO(2) and SiN(x) layers and a metal cathode together with the microlens array. Electroluminescence of the devices showed that color variation under the viewing angle due to the microcavity is suppressed remarkably by microlens arrays, which makes the use of devices acceptable in many applications. It was also demonstrated that the external out-coupling factor of the devise increases by a factor of ~1.8 with wide viewing angles compared to conventional OLEDs.
Optics Express 08/2006; 14(14):6564-71. · 3.59 Impact Factor
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ABSTRACT: When an electron beam is generated from a cathode, an electron sheath plasma is also generated so that perveance of the diode is varied and changes the diode output characteristics. In our pulse power system "Chundoong" (Max 600 kV, 88 kA, 60 ns), the perveance value have been experimentally investigated and estimated from diode voltage and diode current. In this experiment, the anode- cathode (A-K) gap distance d has been varied from 4 mm to 10 mm. It is noted in this experiment that the diode perveance characteristics could be described as 7.0×10<sup>-9</sup>/d<sup>1.82</sup>. The sheath plasma expansion speed has also been estimated from the experiment, which is to be about 7 cm/us under A-K gap distance 4 mm.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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ABSTRACT: We have investigated an influence of anode-cathode (A-K) gap distance on output characteristics of high power microwave from coaxial virtual cathode oscillator (vircator). This high power microwave generator is powered by the 'Chundoong' (Max 600 kV, 88 kA, 60 ns), which is an intense relativistic electron beam-pulse generator. In this experiment, we observed that the microwave power has been dependent upon the A-K gap distance, where A-K gap has been varied from 4 mm to 10 mm. The maximum microwave power is observed to be 240 MW, whose efficiency is about 3.45%, at the AK gap distance of 4 mm. Also the microwave frequencies are measured to be 5.7 GHz from combination of coupled line band pass filter with 1 GHz band-gap and dispersive delay line. It is noted that and this measured frequency is in good agreement with that of simulation. It is also found that the dominant mode of output microwave is a TM01 mode from both results of experiment and simulation.
Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
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Eun Ha Choi,
Myung Chull Choi,
Sung Hyuk Choi,
Kie Back Song,
Yoon Jung, Yoon Ho Seo,
Hee Myung Shin,
Han Sup Uhm,
Dong Woo Lim,
Chun Ho Kim,
Jae Min Lee,
Jae Woon Ahn
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ABSTRACT: When an electron beam is generated from a cathode, an electrode sheath plasma is also generated. Hence, the perveance of the diode is varied and changes the diode output characteristics. In our pulsed-power system "Chundoong," the perveance characteristics have been experimentally investigated, from which the sheath-plasma expansion speed has been measured to be about 3 cm/μs inside the diode. It is shown that the sheath-plasma expansion inside the diode gives the influence on the electron-beam current density. The vircator microwave output has been shown to be sensitively dependent on the anode-cathode (A-K) gap distance. The highest microwave power occurs at the initial A-K gap distance d=4 mm with peak power of 200 MW and a frequency of about 5.5 GHz in this experiment.
IEEE Transactions on Plasma Science 11/2002; · 1.17 Impact Factor
