Photoluminescence characteristics of Ir(ppy)3 and PtOEP doped in TPD host material

Thin films of triphenylamine dimer, N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-benzidine (TPD), fac tris(2-phenylpyridine) iridium (Ir(ppy)3) doped TPD, and platinum octaethyl porphine (PtOEP) doped TPD have been characterized by photoluminescence measurements at several excitation wavelengths in the temperature range from 10 K to room temperature. The investigated doped films are phosphorescent OLED materials whereby TPD acts as triplet reservoir for Ir(ppy)3 (endothermic transfer system) and as pathway intermediate for PtOEP (exothermic transfer system). At low temperature, phosphorescence of TPD was observed. At short-wavelength excitation, where TPD is absorbing, Förster-type energy transfer to Ir(ppy)3 and PtOEP was resolved. The temperature-dependent phosphorescence studies revealed Dexter-type triplet–triplet forth and back excitation transfer between Ir(ppy)3 and TPD and are compatible with Dexter-type triplet–triplet forward excitation transfer from TPD to PtOEP.