Shang Hyeun Park

Paper as a Substrate for Inorganic Powder Electroluminescence Devices

Alternating-current-type inorganic powder electroluminescence (PEL) devices were successfully fabricated on four kinds of paper substrates, i.e., glossy paper, sticker paper, magazine paper, and newspaper. To protect the paper from wet chemical and heating processes during the formation of the PEL device, the paper substrate was coated with a spin-on-glass layer that served as a buffer layer. In spite of the fragility of paper, quite satisfactory results were obtained-the performance of paper-based PEL devices was almost equivalent to that of PEL devices on a plastic substrate. Extension of a substrate to paper, even to flimsy daily newspaper, will widen the opportunity of PEL devices as one of flexible and disposable displays.

Carbon nanotube induced enhancement of electroluminescence of phosphor

Electroluminescence(EL) was observed on conventional cathodoluminescent (CL)phosphor with the incorporation of carbon nanotube(CNT) at ambient air. The role of CNT can be understood as enhancing the local electrical field, which allows electron injection to the active center of phosphor at relatively low operating voltages. In this EL device, the brightness of CLphosphor was significantly improved from no light emission in the case of no addition of CNT to 35 cd / m 2 with 1 wt % CNT at 10 kHz of ac 300 V.

A chlorinated barium titanate-filled polymer composite with a high dielectric constant and its application to electroluminescent devices

We have studied the effect of chlorination on the dielectric performance of a barium titanate (BTO)–polymer film. Functionalization of BTO powder particles with chlorine (Cl) atoms and/or Cl-containing functional groups was achieved by a simple treatment using chlorinated solvents. The chlorinated BTO (Cl-BTO) particles were incorporated into a cyanoethyl-based polymer and the mixture was spin-coated to produce a composite film. The dielectric constant of the composite film with Cl-BTO was as high as 208 at a frequency of 10 Hz, showing a 2.5-fold increase in dielectric constant compared to composites composed of the neat BTO and the cyanoethyl-based polymer at a frequency of 10 Hz. The observed dramatic increase in dielectric constant would be caused by the interfacial polarization due to the p-type doping effect resulting from the presence of strong electronegative Cl atoms. Given a relatively high dielectric constant, composite films with Cl-BTO were further exploited as a dielectric layer in an inorganic electroluminescence (EL) device. The luminance of the EL device with Cl-BTO was 4090 cd m−2 at a frequency of 1 kHz, showing a 2.03-fold increase in luminance compared to that with the untreated BTO. The improved performance of the EL device is attributed to a high dielectric constant of the composite films that allow for efficient charge carrier tunneling into the phosphor and therefore enhanced luminance and efficiency.

High electroluminescence of the ZnS:Mn nanoparticle/cyanoethyl-resin polymer/single-walled carbon nanotube composite using the tandem structure

The EL performance of the tandem structured phosphor/polymer/SWCNT composite was greatly increased by structural and material effects, which led to increased tunneling charge carriers into phosphor, resulting in improved luminance. The tandem structured composite EL device exhibited a 1570% increase in the luminance compared to the raw phosphor EL device.

Field-Enhancement Effect of Short Carbon Nanotubes Using an Electrical Aging Treatment on Inorganic Electroluminescence

AC inorganic electroluminescence (EL) devices were fabricated using the emitting layer composed of phosphor-single-walled carbon nanotubes (SWCNTs) composite (PSC) to utilize the local field enhancement of SWCNTs. In order to enhance the electric field in an emitting layer with minimized current paths, bare long SWCNTs were shortened by cryogenic crushing method. After electrical aging treatment of the PSC device, partly formed short SWCNT networks in the emitting layer were effectively removed during the electrical aging treatment. High performance of 60% and 43% increase in efficiency and luminance, respectively, was achieved. This PSC device with short SWCNTs could lead to high brightness due to increased electron tunneling into phosphor. The PSC device reveals the importance of high electric field by SWCNTs leading to high EL performance.

Correlation of the optical gap of (Ba,Sr)yTiO2+y thin films with film composition

A series of 26 (Ba1−xSrx)yTiO2+y thin films with 0.22≤y≤1.01 and x<0.07 were grown by metalorganic chemical vapor deposition. Most of the films with 0.22≤y≤0.37 were fully amorphous, whereas the films with 0.43≤y<1 were composed of crystalline (Ba,Sr)TiO3 and a Ti-rich amorphous phase. Transmission spectra were measured and analyzed to determine the optical constants of the films, including the optical gap, which was found to decrease as y increased. An effective medium model was used to estimate the volume fraction of amorphous material in the two-phase films from the transmission spectra, by assuming that the two phases each had a fixed optical gap.

Enhanced Optical and Electrical Properties of Inorganic Electroluminescent Devices Using the Top-Emission Structure

Alternating current inorganic powder electroluminescence (EL) devices with a top-emission structure were fabricated on glass substrates to investigate the structural dependence on EL. The EL performance was examined by comparing the top-emission structure with the conventional EL device, i.e., the bottom-emission structure. High performance, such as 50 and 40% increases in efficiency and brightness, respectively, was achieved. This enhanced EL performance was attributed to the structural change in the EL device, leading to reduced optical loss and enhanced electric field applied to the phosphor.

Improvement of the dielectric properties of BaTiO 3 powder-polymer composite using molten salt treatment

The dielectric films consisted of the barium titanate (BaTiO3) powder particle and the polymer were fabricated using the sodium chloride (NaCl)-flux treatment to investigate the effect of the molten salt on the dielectric properties of the BaTiO3 particles. The BaTiO3 particles for the NaCl-flux treatment were prepared by calcining the mixture of the BaTiO3 and the NaCl at the various temperatures. The NaCl-flux treated BaTiO3 particles showed the smooth surface and high crystallinity compared to the non-treated BaTiO3 particles, because the BaTiO3 particles were recrystallized by NaCl-flux treatment. In addition, high dielectric performances of a 20% increase in the dielectric constant, a 40% decrease in the dielectric loss, and a 280% increase in the dielectric strength were achieved. The dielectric films of the NaCl-flux treated BaTiO3 particles could induce the high dielectric performances due to the improvement of the crystallinity with highly packing density.

Controlled Vacuum Breakdown in Carbon Nanotube Field Emission

We report a physical mechanism of controlling vacuum breakdown in field emission from carbon nanotubes (CNTs). The thermal evaporation or runaway of CNT emitters is considered to be responsible for destructive vacuum breakdowns due to an overcurrent through electronically shorted circuits, where misaligned or irregularly long CNT emitters were found. The occurrence of the destructive breakdown, however, could be under control after an electrical treatment using soft breakdowns. Significant improvements of field emission stability and uniformity were achieved by optimally controlled soft breakdowns, which eliminated the short circuits and recovered the field emission with no destruction of electrodes.

P‐108: High Performances of the Powder Electroluminescence Device using the Carbon Nanotubes

The display characteristics of AC powder electroluminescence (EL) devices were improved by adopting nanomaterials, here single walled carbon nanotubes (CNTs). CNTs were shortened by the cryo-crushing method in order to reduce unnecessary current bypath networks which might be formed by long pristine CNTs. Two approaches utilizing CNTs were investigated—a CNT layer was inserted between an emitting layer and a dielectric layer, and CNT-phosphor composite was used as an emitting layer. Both methods improved the brightness and current density of EL devices (20% brighter and 10% less current density than the reference device). This might be caused by the characteristics of nanomaterials, i.e., high local electric field near the end of nanomaterials and high surface to volume ratio.