We propose an emitting assist (EA) dopant system for obtaining organic light-emitting diodes (OLEDs) with pure red emission. The EA dopant (rubrene) did not itself emit but assisted the energy transfer from the host (Alq3) to the red emitting dopant (DCM2). The cell structure used was {indium tin oxide/hole injection layer [(20 nm), CuPc/hole transport layer (50 nm), NPB/emitting layer (40 nm), Alq3+DCM2 (2%)+rubrene (5 wt %)]/MgIn}. (CuPc: Copper (II) phthalocyanine, NPB: N, N′-Di(naphthalen-1-yl)-N, N′-diphenyl-benzidine, DCM2: 4-Dicyanomethylene- 2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-8-yl)vinyl]-4H-pyran). A stable red emission (chromaticity coordinates: x=0.64, y=0.36) was obtained in this cell within the luminance range of 100–4000 cd/m2. When the cell was not doped with rubrene, the emission color changed from red to orange as the luminance increased. The EA dopant system is a promising method for obtaining red OLEDs.

Fluorescent metal complexes and dimers have been synthesized and used for organic light-emitting diodes. The metal complexes with conjugated molecular ligands have strong photoluminescence, and showed bright emission of over 10 000 cd m 22 in bilayer electroluminescent (EL) cells. The EL cell structure was [transparent anode/hole-transport layer/emitting layer/cathode]. The newly synthesized pyrazoline dimers are also highlȳ uorescent, and they have hole-transport tendency. Therefore, another type of structure [transparent anode/ emitting layer/electron-transport layer/cathode] was applied to get emission from the pyrazoline derivatives. As a result, one pyrazoline derivative showed bright blue EL of 1700 cd m 22 at the maximum when it was combined with an oxadiazole electron-transport material.

A gallium complex (GaMq2Cl) consisting of two 2-methyl-8-hydroxyquinolines (Mq) and a chlorine was synthesized and used for the fabrication of organic light-emitting diodes (OLEDs). The photoluminescent peak of GaMq2Cl at 492 nm was as strong in intensity as that of tris(8-hydroxyquinolinato)aluminum (Alq3). The OLED using GaMq2Cl as an emitting material showed blue-green luminance of 10 490 cd/m2. When it was used as an electron transport material in a rubrene doped cell, an OLED with a high luminance of 27 700 cd/m2 was obtained. We found that GaMq2Cl also was useful as a host material.

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We consider the polarization of unstable type-IIB D0-branes in the presence of a background five-form field strength. This phenomenon is studied from the point of view of the leading terms in the non-abelian Born Infeld action of the unstable D0-branes. The equations have SO(4) invariant solutions describing a non-commutative 3-sphere, which becomes a classical 3-sphere in the large-N limit. We discuss the interpretation of these solutions as spherical D3-branes. The tachyon plays a tantalizingly geometrical role in relating the fuzzy S 3 geometry to that of a fuzzy S 4 .