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AC driven inorganic electroluminescence (EL) of the carbon nanotube (CNT)-polymer/phosphor composite was fabricated to investigate the effect of the critical percolation threshold by CNT concentration on EL performance. In order to control the appropriate CNT condition in EL device, CNTs were shortened by cryogenic crushing and purified by thermal treatment. Among various CNT concentrations in the composite film, the critical percolation threshold can be found to be 0.0925 wt.% by fitting conductivity data of the composite film. Near the critical percolation threshold of a CNT concentration, the EL performances of the composite EL were greatly increased compared to the reference EL. The tunneling barrier thickness at the ZnS–CuxS contact could become thin to induce more charge carrier tunneling into ZnS host lattice by the local field enhancement of CNTs, resulting in increased electron–hole recombination to produce more light emission.

An alternating current driven electroluminescence (EL) device consisting of a phosphor dispersed in a polymer matrix device was fabricated as a tandem structure. This structure can be formed by duplicating the emitting and conducting layers. The EL device with the tandem structure, particularly the device with the triple emitting layer, was six times brighter than (1460 cd/m 2 at an alternating voltage application of 50 V) the structure with a single emitting layer. This tandem structure plays important roles by increasing the chance of electron–hole tunneling into the phosphor with leading to an increase in brightness by combining the light emitted from several emitting layers in a device. In addition, the adoption of a spin-coating method for the deposition of an emitting layer can allow the production of a dielectric part on the lower-lying emitting phosphor powder particles. The implementation of a dielectric part and emitting part by one spin-coating procedure simplifies the overall fabrication process, particularly for the tandem structure. The significant increase in brightness with each additional emitting layer as well as a facile fabrication process would help to make the EL device a competitive candidate in future displays and lightings.

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.

An inorganic electroluminescent (EL) device on a flexible polyethylene terephthalate (PET) substrate and its properties were investigated. The transparent conducting film (TCF) made from carbon nanotubes (CNTs) (CNT-TCF) was employed in the flexible EL device. CNT-TCF was formed by filtration of CNT solution and was transferred to the PET film. It was found that the brightness of the inorganic EL device was strongly dependent on the quality of the CNT composite films. After a 3-aminopropyltriethoxysilane treatment of the PET substrate, CNTs uniformly were dispersed and showed a good adhesion to the substrate, and the resulting EL device showed better performance. The flexible EL device showed the brightness of 96.8 cd/m2 at 28 kHz and 50 V.

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.

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.

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.

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.

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.

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.