Ki Wan Park

Formation of large-volume, high-pressure plasmas in microhollow cathode discharges

We have developed two electrode configurations that employ one primary supply circuit with a variable resistor for large-volume, high-pressure glow discharges without glow-to-arc transitions, and have investigated their electrical and the photoimages in microhollow cathode sustained discharges. The applied voltage and the discharge current between electrodes were controlled by changing the resistance of a variable resistor, which could replace the secondary supply circuit in microhollow cathode sustained discharges for the formation of secondary discharge. The electrical and the optical measurements showed that the discharge passed through three distinct stages: no discharges, microhollow cathode discharges, and microhollow cathode sustained discharges. Compared with the two-supply circuit system that has a primary and a secondary supply circuit, this electrode configuration is very simple and inexpensive process in generating large-volume plasmas at high pressures.

Highly efficient organic light-emitting diodes with a quantum dot interfacial layer

Advanced organic light-emitting diodes (OLEDs), based on a multiple structure, were achieved in combination with a quantum dot (QD) interfacial layer. The authors used core/shell CdSe/ZnS QDs passivated with trioctylphosphine oxide (TOPO) and TOPO-free QDs as interlayers. Multiple-structure OLEDs (MOLEDs) with TOPO-free QDs showed higher device efficiency because of a well-defined interfacial monolayer formation. Additionally, the three-unit MOLED showed high performance for device efficiency with double-structured QD interfacial layers due to the enhanced charge balance and recombination probability.

Dielectric barrier hollow cathode discharge and its enhanced performance for light source

We invented the dielectric barrier hollow cathode discharge (DBHCD) configuration as a novel light source and studied on the physical properties of discharge and the possibility of the parallel operation of many holes of the DBHCD without additional impedances such as inductance or capacitance. The electrical characteristics and the photo images of discharges sustained in cavity were investigated. The experimental result showed that the surface discharge mode was transformed into a hollow cathode mode according to a decrease of the pD (operating pressure times hole diameter). The parallel operation of the 13 arrays of DBHCD was also possible without additional impedances for limiting current. We measured the relative IR emission efficiency of the coplanar dielectric barrier discharge (CDBD) and DBHCD to evaluate the enhanced performance as light sources. According to the experiment, the 25 arrays of DBHCD result in 30%-enhanced performance in IR emission efficiency compared with CDBD.

Self-expanded microcapillary positive column for highly efficient vacuum ultraviolet sources

We adopted the self-expanded microcapillary positive column from single microhollow cathode discharge as a high efficient vacuum ultraviolet (vuv) sources, employing one power supply circuit with a resistor for easily starting without an additional power supplier and investigated their electrical characteristics and the vuv radiant efficiency, varying the input power. The electrical measurements showed that the discharge passed through two distinct stages: the microhollow cathode discharges stage and the self-expanded microcapillary positive column stage. As a result, the vuv radiant efficiency of the self-expanded microcapillary positive column is about 17 times as high as that of the microhollow cathode discharges at the input power 1.2W.

Improvement of the vacuum ultraviolet efficiency of low pressure Xe discharge by nitrogen admixture

We investigated Xe–N2 gas discharge primarily as a source of vacuum ultraviolet for florescent lamps. The discharge performances of Xe based nitrogen admixture gas are improved when compared with the results of pure Xe discharge. The experimental results come from investigating the Xe positive column and were determined by measuring the infrared radiation during the discharge operation. These results suggest that the integrated infrared area is increased by about 40% under optimal conditions. This efficiency increase occurs because low energy electrons contribute to the production of exited nitrogen, which can excite Xe gas.

Formation of stable direct current microhollow cathode discharge by venturi gas flow system for remote plasma source in atmosphere

We introduce a microhollow cathode configuration with venturi gas flow to ambient air in order to obtain glow discharge at atmospheric pressure. Stable microhollow cathode discharge was formed in a 200μm diameter at 9mA and the optimum value of gas velocity×diameter for hollow cathode effect was obtained in our system. In order to confirm hollow cathode effect, we measured the enhancement of E∕N strength for 200μm (0.31m2∕s) and 500μm (0.78m2∕s) air discharge at 8mA under the velocity of 156m∕s. As a result, an increase of 46.7% in E∕N strength of the discharge of 200μm hole was obtained compare to that of 500μm.

A study on double hollow electrode discharge and the enhanced performance for electric discharge lamps

We invented a double hollow electrode lamp (DHEL), applied an electron oscillation effect and measured its I?V curve in dc driving to evaluate the electrical characteristics. The volume discharge of this lamp showed an abnormal glow characteristic. Based on these results, we made a 9-channel flat panel lamp and confirmed the possibility of a parallel operation. In order to evaluate the enhanced performance of the DHEL, we compared it with a single hollow triode lamp and a diode lamp (DL). We measured the breakdown voltage, tube current and IR intensity of these three types of lamps. The DHEL showed the lowest breakdown voltage among the three lamps and a higher tube current than that of the DL. The IR intensity of the DHEL was more efficient than that of the DL; the enhanced quantity of efficiency was 11.8% at 0.922?W.

I-P relationship and effective capacitance in external electrode fluorescent lamp

The authors derived an analytical relationship between rms tube current and input power for various capacitances of the external electrode part and measured their effective capacitances in an external electrode fluorescent lamp. From the fitting derived relation in the measured data, the reliability of the authors’ derivation was certain and effective capacitances were measured. Consequently, it is confirmed that the derived relationship is very useful in estimating the effective capacitance of the external electrode part for any shape of glass tube and electrodes during the lamp operation.

Application of microholes in sustain electrode to improving UV efficiency in macroscopic plasma display panel cells

A front-panel structure with microholes in its sustain electrode for use as a macroscopic plasma display panel to achieve high UV radiation efficiency through the micro-hollow effect is proposed. When the Xe/Ne/Ar (4/76/20) pressure is 50 Torr and the driving frequency is AC 20 kH, compared with a conventional structure, the electrode with a microholes produces a high IR intensity and low a electron energy. The excitation energy measured by optical emission spectroscope is 1.4 eV. The IR intensity of the structure with microholes is about 20% higher than that of conventional plasma display panel cells.

Lowering the ignition voltage by the dual microhollow cathode configuration for multichannel flat panel lamp

We have developed a dual microhollow cathode configuration, employing one power supply circuit with a resistor that is suitable for lamp starting without additional power supplier. We also investigated their electrical characteristics and photo images, varying the applied voltage. The electrical and optical measurements showed that the discharge passed through four distinct stages: no discharges, the first microhollow cathode discharges, the both of the first and second microhollow cathode discharges, and finally the main discharge. As a result, the Vs and Es∕p of a dual microhollow configuration were lower by a factor of about 2 than those of a diode at 40Torr. We have also observed that the parallel operation can be possible with a single resistor in nine channels flat panel lamp.