Observation of near infrared and enhanced visible emissions from electroluminescent devices with organo samarium(III) complex

Samarium (dibenzoylmethanato)₃ bathophenanthroline (Sm(DBM) ₃ bath) was employed as an emitting and electron transport layer in organic light emitting diodes (OLEDs), and narrow electroluminescent (EL) emissions of a Sm³⁺ ion were observed in the visible and near infrared (NIR) region, differing from those of the same devices with Eu ³⁺- or Tb³⁺-complex EL devices with the same structure. The EL emissions of the Sm³⁺-devices originate from transitions from ⁴G_5/2 to the lower respective levels of Sm³⁺ ions. A maximum luminance of 490 cd m^-2 at 15 V and an EL efficiency of 0.6% at 0.17 mA cm^-2 were obtained in the visible region, and the improved efficiency should be attributed to introducing a transitional layer between the N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′- diphenyl-4,4′-diamine (TPD) film and the Sm(DBM)₃ bath film and the avoidance of interfacial exciplex emission in devices. Sharp emissions of Sm³⁺ ions in the NIR region were also observed under a lower threshold value less than 4.5 V. © 2006 IOP Publishing Ltd.