Chung Sock Choi

Improved light extraction efficiency in organic light emitting diodes with a perforated WO3 hole injection layer fabricated by use of colloidal lithography.

We present an organic light emitting diode with a perforated WO3 hole injection layer to improve the light extraction efficiency. The two-dimensionally perforated WO3 layer was fabricated by use of colloidal lithography. The light extraction efficiency was improved due to Bragg scattering of waveguide modes and surface plasmon polaritons, and the operating voltage was also decreased. As a result, the external quantum efficiency and the power efficiency were increased as compared with those of conventional organic light emitting diodes without WO3 layer. The angular dependence of emission characteristics was investigated by measuring radiant intensity profiles for emission angles and azimuthal angles.

Surface plasmonic controllable enhanced emission from the intrachain and interchain excitons of a conjugated polymer

We demonstrate selectively enhanced emission by controlling the intrachain and interchain excitons of a conjugated polymer through adjusting surface plasmons. Enhanced light emission from the intrachain excitons was observed by coupling the localized surface plasmon resonance with the intrachain band of the conjugated polymer using Ag nanoparticles. Light emission from the interchain excitons was enhanced by exploiting both the increased strength of the interchain dipole due to the image dipole and the coupling between excitons and surface plasmon polaritons (SPPs). As the Ag nanostructures become complete films, light emission from the interchain excitons increased.

Extracting optical modes of organic light-emitting diodes using quasi-periodic WO 3 nanoislands

Quasi-periodic WO(3) nanoislands are introduced to extract two optical modes in organic light-emitting diodes. The nano-scaled and size-tunable WO(3) islands were fabricated by use of wet-etching with self-aggregated Ag mask. The improvement of light extraction efficiency originates to the recovery of light losses which are surface plasmon mode and waveguide mode. As a result, external quantum efficiency and power efficiency were increased. No changes in emission spectrum and CIE color coordinates with WO(3) nanoislands at various observation angles are desirable if this device is to be utilized in optical system. Furthermore, cost-effective fabrication makes it possible to adopt this system in large area fabrication.

Study on Pulse Waveforms for Improving Voltage Margin and Luminous Efficacy in an AC Plasma Display Panel Having Auxiliary Electrodes

New pulse waveforms applied to an alternating-current plasma display panel (ac PDP) with an auxiliary electrode are investigated for the purpose of improving the panels operating voltage margin and luminous efficacy. In the proposed pulse waveforms with reciprocal sustain pulses, a pair of positive and negative sustain pulses is applied to the sustain electrodes simultaneously and alternately. A positive auxiliary pulse is applied to the auxiliary electrode immediately after reciprocal sustain pulses. The voltage margin becomes wider, and the luminous efficacy is improved because of the suppression of the discharge toward the address electrode. In the another proposed pulse waveforms with reciprocal sustain and auxiliary pulses, a negative pulse, which is the same as the negative pulse of reciprocal sustain pulses, is additionally applied to the auxiliary electrode when reciprocal sustain pulses are applied. This negative auxiliary pulse can maintain a high level of luminous efficacy because it supports the effect of the auxiliary pulses. The measurement results show that the operating voltage margin is about twice wider than that of the typical pulse waveforms for an ac PDP with an auxiliary electrode; furthermore, the maximum luminous efficacy is able to reach 3.14 lm/W in terms of the measurement of the discharge in a 50-in XGA resolution (0.27 mm × 0.81 mm) panel with a white cell and a gas mixture of Ne+20%Xe.

Advanced discharge modes in an ac plasma display with an auxiliary electrode

The characteristics of advanced discharge modes were investigated through measurements of spatiotemporal infrared emission, discharge current, infrared intensity, and luminous efficacy in an ac plasma display panel with an auxiliary electrode located between scan and common electrodes. Pulse waveforms that included auxiliary pulses applied to the auxiliary electrode after every sustain pulse were used. The proposed advanced discharge modes are as follows: In mode 1, strong discharges are generated by the sustain pulses only, whereas strong discharges are generated by the sustain pulses and a weak discharge is generated by the auxiliary pulse applied after the scan pulse in mode 2. In mode 3-1, strong discharges are generated by the sustain pulses and weak discharges are generated by the auxiliary pulses applied after the scan and common pulses, while all sustain and auxiliary pulses generate discharges having similar intensities in mode 3-2. Mode 1 and mode 2 are efficient modes; the luminous efficacy was...

Effects of Various Sustain Electrode Gaps on the Discharge Characteristics of an AC PDP With an Auxiliary Electrode

The effects of sustain electrode gap variation on discharge characteristics were investigated in an ac plasma display panel (PDP) with an auxiliary electrode. In this experiment, the following variations were used for the sustain electrode gap of the PDP with an auxiliary electrode: 120, 140, 170, and 200 mum. Static margin, IR intensity, luminance, and power density were measured and investigated in relation to the sustain electrode gap variation. In all the various sustain electrode gaps, when a proper pulse is applied to an auxiliary electrode, luminous efficacy exceeds the levels achieved in the case of a floated auxiliary electrode. In the case of the shorter sustain electrode gaps of 120 and 140 mum, the improved luminous efficacy is mostly due to an increase in luminance. In the case of the longer sustain electrode gaps of 170 and 200 mum, the improved luminous efficacy is mostly due to a decrease in power density. As the sustain electrode gap increases, the operating sustain voltage becomes higher. On the other hand, the luminous efficacy increases when a proper pulse is applied to the auxiliary electrode.

P‐91: AC Plasma Display Panel with Gold Nano‐particles Inserted into an MgO Protective Layer

A modified MgO structure incorporating gold nano-particles is proposed in this work. By inserting gold nano-particles into the MgO protective layer, dozens of nanometer-scale bumps are created on its surface. The change in the morphology due to these bumps induces a higher secondary electron emission rate, which both increases the luminous efficacy and causes a 20 V reduction of the driving voltage.

Effects of Auxiliary Electrode Width in AC Plasma Display Panels With Auxiliary Electrodes

We investigated the effects of changing the width of the auxiliary electrode in an ac plasma display panel including centrally located auxiliary electrodes between the sustain electrodes, based on analyses of the discharge mode. A panel with auxiliary electrodes was driven by pulse waveforms that included auxiliary pulses applied to the auxiliary electrode immediately after every sustain pulse. The discharge modes are changed consecutively from mode 1 to mode 3-2 when the sustain or auxiliary pulse voltages are increased, which can be characterized as follows: 1) only the sustain pulse discharges are generated in mode 1; 2) one of a pair of the auxiliary pulse discharges is additionally generated in mode 2; and 3) the other auxiliary pulse discharge is also generated in mode 3-1 and mode 3-2. Distribution of the discharge mode changes in accordance with the width of the auxiliary electrode (the focus is on modes 1 and 2 because these modes are effective modes); as the auxiliary electrode is narrowed, the range of mode 1 becomes wide and the range of mode 2 becomes narrow. The wide range of mode 1 is attributed to the fact that the discharge of the auxiliary pulse is suppressed due to a longer gap between the sustain and auxiliary electrodes. The narrow range of mode 2 is caused by the discharge of the auxiliary pulse less affecting the discharge of the sustain pulse. Since the auxiliary electrode provides less of a decrease in the number of wall charges on the sustain electrodes, the voltage margin is improved for the case of the narrow auxiliary electrode. The luminous efficacy is mostly improved in mode 1 for the case of the narrow auxiliary electrode due to the auxiliary pulse with a higher voltage generating a larger number of space charges, as well as in mode 2 for the case of the wide auxiliary electrode due to a short electrode gap rendering a great number of wall charges decreasing.

P‐134: Dependency of Auxiliary Pulse Width on Luminous Efficacy in AC Plasma Display Panel

The width of the pulse applied to an auxiliary electrode was varied to investigate the characteristics of luminous efficacy of an AC plasma display with an auxiliary electrode in accordance with the frequency and duty factor of the sustain pulse. The auxiliary voltage margin increased with an increase in the sustain pulse width and a decrease in the auxiliary pulse width. In addition, the luminous efficacy increased with a decrease in the sustain pulse width and an increase in the auxiliary pulse width, except when the time interval between the auxiliary pulse and the subsequent sustain pulse is zero.

P‐129: The Effect of Front Dielectric Thickness on Luminous Efficacy in AC PDP with Auxiliary Electrode

The dependence of front dielectric thickness on input power density, luminance, and luminous efficacy according to the voltage of the auxiliary pulse in an AC PDP with an auxiliary electrode was investigated. It was found that two important factors influencing the luminous efficacy due to variation of the front dielectric thickness. One is the range of the voltage of the auxiliary pulse within which the power density decreases, but the luminance slightly increases, which improve the luminous efficacy. The other is the transmittance reducing the luminance as front dielectric thickness increased, leading to a decrease in the luminous efficacy. In this work, considering these two factors, the luminous efficacy is maximized at a front dielectric layer thickness of 40μm.