Blue electroluminescent devices made from a naphthyl-substituted benzidine derivative and rare earth metal chelates

Electroluminescent (EL) devices with a bi-layer structure were fabricated using N,N′-bis(1-naphthyl)-N,N′-diphenyl- 1,1′-biphenyl-4,4′-diamine (NPB) as a light-emitting and hole-transporting layer and a rare earth (RE) metal chelates (tris(acetylacetonato)-(monophenanthroline) RE(III) (RE(ACA)₃phen; where, RE is Y, La or Gd), as the electron-transporting layer. For the device using the Gd complex, blue EL emission with a maximum luminance of over 1000 cd/m² was achieved at approx. 22 V. The effects of using the yttrium and lanthanide complexes instead of the Gd complex on the EL emission spectra were discussed.