HIGHLY EFFICIENT PHOSPHORESCENT EMISSION FROM ORGANIC ELECTROLUMINESCENT DEVICES

The efficiency of electroluminescent organic light-emitting devices(1, 2) can be improved by the introduction(3) of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the s inglet spin states induce fluorescent emission; these represent a smal l fraction (about 25%) of the total excited-state population (the rema inder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may re sult from both singlet and triplet states. Here we report high-efficie ncy (greater than or similar to 90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP ). Our doped electroluminescent devices generate saturated red emissio n with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphoresc ent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behav iour and energy transfer in organic solid-state systems.