ELECTRONIC EXCITATIONS IN LUMINESCENT CONJUGATED POLYMERS

We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layer in electroluminescent diodes, L EDs. Photoluminescence efficiencies above 60% for solid films of PPV a re now achieved and single-layer EL diodes achieve luminous efficienci es above 2 Lumen W-1 and peak brightnesses up to 90 000 cd m(-2). We d iscuss measurements of photoconductivity, photovoltaic response, photo luminescence excitation spectra and stimulated emission in films of PP V. We consider that the photoexcited state in these films of PPV is th e intrachain singlet exciton. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments and can be used as the active lasing medium when incorporated in suitable microcavity structures. (C) 1997 Elsevier Science Ltd.