Virginia TechZenz, C.Cerullo, G.Lanzani, G.Graupner, W.Meghdadi, F.Leising, G.De Silvestri, S.2014-05-072014-05-071999-06Zenz, C.; Cerullo, G.; Lanzani, G.; Graupner, W.; Meghdadi, F.; Leising, G.; De Silvestri, S., "Ultrafast photogeneration mechanisms of triplet states in para-hexaphenyl," Phys. Rev. B 59, 14336 DOI: http://dx.doi.org/10.1103/PhysRevB.59.143360163-1829http://hdl.handle.net/10919/47905We present femtosecond pump-probe measurements, both conventional and electric field-assisted, on organic light-emitting devices based on para-hexaphenyl. The dominant triplet excition generation mechanism is assigned to nongeminate bimolecular recombination of photogenerated, spin-1/2 polarons. This process is active within a few hundred femtoseconds after photoexcitation and involves about 20% of the initially excited states. At higher photoexcitation densities, we observe an additional triplet generation mechanism, which occurs in the 10-ps time domain, due to fusion of singlet excitons and subsequent fission into correlated triplet pairs. The latter decay on the 10(2)-ps time scale by geminate recombination.application/pdfenIn Copyrightfield-induced dissociationconjugated polymerspoly(p-phenylene)oligomersdynamicselectroluminescencefilmspoly(para-phenylene)photoexcitationstransitionsgenerationphysics, condensed matterArticle - Refereedhttp://journals.aps.org/prb/abstract/10.1103/PhysRevB.59.14336https://doi.org/10.1103/PhysRevB.59.14336