Light-emitting diodes and lasers based on polymer films doped with small organic molecules and rare-earth complexes

Abstract

We investigated the lasing properties of optically pumped polymer films. Amplified spontaneous emission (ASE) around 400 nm was observed in polymer films of polystyrene (PS) and poly(N-vinylcarbazole) (PVK) doped up to 20% with the hole-transporting organic molecule N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD). Thus, TPD-based films are candidates for blue-emitting organic diode lasers. Films containing several semiconducting organic molecules and polymers and rare-earth complexes were also investigated. Energy transfer was observed in PVK films doped with various europium and samarium complexes. PS films containing the electron-transporting organic molecule 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and small amounts of TPD also showed energy transfer to the europium complexes, but not to the samarium ones. None of these films demonstrated ASE; therefore, they are not appropriate for lasing purposes. However, because rare-earth ions have very sharp emission spectra, these materials are candidates for very monochromatic light-emitting diodes.