An alternative method for producing efficient white light-emitting polymer diodes based on a blend of two polymers is reported. The white light emission is composed of a broad blue emission of laddertype (polyparaphenylene) (m-LPPP) and a red-orange emission of a new polymer, poly(perylene-co-diethynylbenzene) (PPDB). The red-orange electroluminescence emission is promoted by an excitation energy and charge transfer from m-LPPP to the PPDB. A concentration of 0.05% PPDB in the polymer blend is required in order to obtain white light emission. By inserting an insulating material in the blend, so that a maximum external quantum efficiency of 1.2% is obtained.

Blue electroluminescent devices with high quantum efficiency from alkoxysubstituted poly(paraphenylene vinylene)trimers in a polystyrene matrix

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The emission color of polymer-light-emitting diodes ͑PLED's͒ can be tuned by doping the active polymer layer with certain dyes or other fluorescent polymers. We demonstrate the realization of red-orange PLED's by doping a blue-light-emitting ladder-type poly͑paraphenylene͒ ͑m-LPPP͒ with a new red-light-emitting polymer poly͑perylene-co-diethynylbenzene͒ ͑PPDB͒. For PPDB concentrations far below 1 wt % the photo-͑PL͒ and the electroluminescence ͑EL͒ spectrum of the m-LPPP/PPDB blend is already dominated by the PPDB emission because of an excitation energy transfer from m-LPPP to PPDB. The reason for this efficient energy transfer can be explained by the energetic position of the highest occupied and lowest unoccupied states in PPDB relative to the corresponding levels in m-LPPP. Besides the change in the emission color by doping PPDB into m-LPPP, a significant increase in the PL quantum efficiency ͑up to 41%͒ and even a more pronounced improvement of the external EL quantum efficiency of these PLED's ͑up to 1.6%͒ is observed.