Katsuro Okuyama

White light‐emitting organic electroluminescent devices using the poly(N‐vinylcarbazole) emitter layer doped with three fluorescent dyes

White light‐emitting electroluminescent devices were fabricated using poly(N‐vinylcarbazole) (PVK) as a hole‐transporting emitter layer and a double layer of 1,2,4‐triazole derivative (TAZ) and tris(8‐quinolinolato)aluminum(III) complex (Alq) as an electron transport layer. The PVK layer was doped with fluorescent dyes such as blue‐emitting 1,1,4,4‐tetraphenyl‐1,3‐butadiene, green‐emitting coumarin 6, and orange‐emitting DCM 1. A cell structure of glass substrate/indium‐tin‐oxide/doped PVK/TAZ/Alq/Mg:Ag was employed. White emission covering a wide range of the visible region and a high luminance of 3400 cd/m2 were obtained at a drive voltage of 14 V.

BRIGHT RED LIGHT-EMITTING ORGANIC ELECTROLUMINESCENT DEVICES HAVING A EUROPIUM COMPLEX AS AN EMITTER

Organic electroluminescent (EL) devices with a trivalent europium (Eu) complex as an emitter were fabricated. Triple‐layer‐type cells with a structure of glass substrate/indium‐tin oxide/ triphenyldiamine derivative (TPD)/Eu complex: 1,3,4‐oxadiazole derivative (PBD)/aluminum complex (Alq)/Mg:Ag exhibit bright red luminescence upon applying dc voltage. The EL spectrum consists of extremely sharp emission bands, which is a typical luminescence spectrum of the Eu complex. Luminance of 460 cd/m2 with an emission peak at 614 nm is achieved at a drive voltage of 16 V. This is the highest luminance so far obtained for the EL cells having a Eu complex as an emitter.

Bright blue electroluminescence from poly(N‐vinylcarbazole)

Electroluminescent devices were fabricated using poly(N‐vinylcarbazole) (PVK) as a hole‐transporting emitter layer and a double layer of 1,2,4‐triazole derivative (TAZ) and tris(8‐quinolinolato)aluminum(III) complex (Alq) as an electron transport layer. A cell structure of glass substrate/indium‐tin‐oxide/PVK/TAZ/Alq/Mg:Ag was employed. In this cell structure, carrier injection from the electrodes to the PVK layer and concomitant electroluminescence from PVK were observed. Blue emission peaking at 410 nm and a luminance of 700 cd/m2 were achieved at a drive voltage of 14 V.

1,2,4-Triazole Derivative as an Electron Transport Layer in Organic Electroluminescent Devices

Organic electroluminescent devices with multilayer structures were fabricated using a 1,2,4-triazole derivative as the carrier transport layer. 3-(4-Biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ) was found to be electron-transporting, and a cell with a structure of glass substrate/indium-tin oxide/triphenylamine derivative (TPD)/TAZ/Alq/Mg:Ag exhibited bright blue electroluminescence from the TPD layer. A luminance of 3700 cd/m2 with an emission peak at 464 nm was achieved at a drive voltage of 16 V.

Organic electroluminescent devices based on molecularly doped polymers

Electroluminescent devices were fabricated using poly(methyl methacrylate) (PMMA) molecularly doped with triphenyldiamine derivative and tris(8‐quinolinolato)aluminum(III) complex (Alq). A cell structure of glass substrate/indium–tin–oxide/doped PMMA/Mg:Ag was employed. Carrier injection from the electrodes to the doped PMMA layer through the dopants and concomitant electroluminescence from Alq were observed. Green emission with luminance of 920 cd/m2 was achieved at a drive voltage of 17 V.

Hydrogen Gas Sensing Using a Pd-Coated Cantilever

A cantilever consisting of a thin glass plate coated with an evaporated Pd thin film can be utilized as a hydrogen gas sensor because the Pd film expands upon absorption of hydrogen, resulting in the bending of the free end of the cantilever. A comparison has been made between the response obtained experimentally from 100–1000-nm-thick Pd-coated glass plate cantilevers in the presence of 0.1–600 Torr hydrogen and the response calculated from the data of the Pd lattice expansion due to hydrogen absorption and the elasticity theory. It is shown that the Pd-coated cantilever can detect hydrogen at least from 0.1 to 10 Torr with good reproducibility. The use of a Pd–Ag alloy film instead of a pure Pd film was found to be effective both in enhancing the hydrogen sensitivity at low hydrogen pressures and in extending the hydrogen responsivity up to 600 Torr.

Molecularly Doped Polymers for Organic Electroluminescent Devices

Abstract Electroluminescent devices were fabricated using poly(methyl methacrylate) (PMMA) molecularly doped with triphenyldiamine derivative and tris(8-quinolinolato)aluminum(III) complex (Alq). A cell structure of glass substrate/indium-tin-oxide/doped PMMA/Mg: Ag was employed. Green emission with luminance of 920 cd/m2 was achieved at a drive voltage of 17 V. The EL color was tuned to blue-green and yellow-orange by further doping the PMMA layer with suitable organic dyes.

Molecularly Doped Polymers as a Hole Transport Layer in Organic Electroluminescent Devices

Electroluminescent devices were fabricated using polycarbonate or poly(methyl methacrylate) molecularly doped with triphenyldiamine derivative as the hole transport layer and tris(8-quinolinolato)aluminum(III) complex (Alq) as the emitting layer, respectively. A cell structure of glass substrate/indium-tin-oxide/doped polymer/Alq/Mg:Ag was employed. Hole injection from the electrode through the doped polymer layer and concomitant efficient electroluminescence from the Alq layer were observed. Bright green emission with a luminance of 7700 cd/m2 was observed at a drive voltage of 14 V from the cell with the doped polycarbonate layer.

Origin of modulated structure for high-Tc Bi2212 superconductor

Abstract The high-Tc superconductor Bi2Sr2CaCu2Oy is known to have modulated structure. We have systematically investigated modulation period, lattice mismatch, oxygen content and Bi valence and made clear the origin of modulation. The lattice mismatch between the CuO2 plane and the BiO block is relaxed by expanding the BiO block. The expansion is brought about by both insertion of oxygen into the BiO block and a change in Bi valence. The insertion of oxygen leads to formation of the modulation. The decrease in Bi valence leads to the increase in the ionic radius of the Bi.

Hall Mobility of Evaporated Tellurium Films

The Hall mobility of evaporated tellurium films was measured as a function of the temperature ranging from 77 to 300 K, and was compared with the theoretical values based on bulk single crystal theories. The measured Hall mobility was about one-tenth of the theoretical value. This deviation was accounted for by considering the potential barrier scattering model due to the grain boundaries of the polycrystalline films proposed by Petritz.