Tris(dibenzoylmethane)(monophenanthroline)europium(III) based red emittingorganic light emitting diodes

The concept of a blue light emitting diode containing a hole blocking layer (HBL) is generalized to efficiently excite dye molecules introduced in the form of an emission layer on the hole transporting side. The concept allow s the excitation of an emitting molecule even if the molecule does not act primarily as a recombination center. On the basis of this concept pure red emitting organic light emitting diodes were produced utilizing tris(dibenzo ylmethane)(monophenanthroline)europium(III) [Eu(dbm)(3)phen] as the emittin g layer in an Al/LiF/Aluminum tris(8-hydroxyquinoline) (Alq(3))/HBL/Eu(dbm) (3)phen/N,N-'-di(1-naphthyl)-N,N-'-diphenylbenzidine (alpha -NPD)/copper-ph thalo- cyanine (CuPc)/indium tin oxide structure. Additionally, the luminan ce output of such a device was improved by partially adding a hole transpor t material to the emitting layer in order to increase the penetration of ho les into the emission region. A maximum luminance output of 200 cd/m(2) at 15 V was achieved without optimizing the layer thickness. Furthermore, the effect of saturation of the Eu3+ emission is studied and discussed. The bas ic device architecture presented here is expected to work with other transp ort and emitting materials also. (C) 2001 American Institute of Physics.