Exciplex or electroplex emissions from the interface between aromatic diamine and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline?

Organic light-emitting diodes (OLEDs) have been fabricated which consist of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) (TPD), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and tris(8-hydroxyquinoline) aluminum (Alq3). Four emission peaks located at about 401 nm, 425 nm, 452 nm and 480 nm have been obtained in the electroluminescence (EL) spectra of these devices. The former two emissions originate from the exciton emission of TPD molecular. The last two emissions could be attributed to local (LOC) exiplex emission and charge transfer (CT) exiplex emission at the interface between TPD and BCP layers, respectively.