Yoon Ho Seo

Enhanced out-coupling factor of microcavity organic light-emitting devices with irregular microlens array

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.

Characteristics of diode perveance and vircator output under various anode-cathode gap distances

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//spl mu/s 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.

Enhanced light emission from one-layered organic light-emitting devices doped with organic salt by simultaneous thermal and electrical annealing

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.

Double interfacial layers for highly efficient organic light-emitting devices

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 ∼60cd∕A with a current density of 1.6mA∕cm2 and a luminance of 1000cd∕m2 at 6.5V, which is higher than that of a control device with a single CsF interfacial layer.

Highly efficient green phosphorescent single-layered organic light-emitting devices

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 48cd∕A and power efficiency (ηp) of 45lm∕W at a current density of 0.02mA∕cm2. Even at 1000cd∕m2 (2mA∕cm2), high ηc of 50cd∕A and ηp of 22lm∕W were obtained.

Analysis of Striations in a Coplanar Discharge

Striations are observed only in coplanar or wedge-shaped planar AC-type discharges. On the basis of the observation results, striations are analyzed and discovered to be related to the ion waves generated by the self-sustained perturbations during the force-balancing process between ion and electron wall charge clouds accumulated on the dielectric layer over the metal electrodes.

Comparison between Grazing and Off-Grazing Resonance Emissions of Stimulated Superradiance in an Undulator Channel

The effect of bunch slippage in stimulated superradiance emitted from short electron bunches in an undulator channel at the off-grazing resonance is discussed. Comparison between off-grazing and grazing resonance emissions shows that the emitted power in the early radiation-build-up stage significantly decreases owing to the bandwidth restriction caused by slippage. The influence of bunch-pulse detachment due to the slippage seems to be minimized by the proper positioning of the excited pulse.

One-dimensional birefringent photonic crystal laser

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.

Influence of anode-cathode gap distance on output characteristics of high power microwave from coaxial virtual cathode oscillator

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.

P-158: Highly Efficient Ionic p-i-n Phosphorescent OLEDs Made by Solution Processing

We report efficient light-emission from solution-processed single-layered phosphorescent organic light-emitting diodes that were doped with ionic salt and treated with simultaneous electrical and thermal annealing. The simultaneous annealing induced proper formation of an ionic p-i-n structure. As experimental results, brightness and efficiency were improved over 35,000 cd/m2 and 40 lm/W.