Electrophosphorescence emission in organic light-emitting diodes based on (Sm plus Eu) complexes

In this work, we reported the preparation and the characterization of triple-layer electroluminescent organic devices using different blends of the samarium and europium beta-diketonate complexes [SmxEuy(TTA)(3)(TPPO)(2)] (x=0.7, 0.9; y=0.3, 0.1) as emitting layer. The organic light-emitting diode (OLED) devices contained 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1'-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline) aluminum (Alq(3)) as electron transporting layer. The electroluminescence (EL) spectra present emission narrow bands characteristic of the Sm3+ and Eu3+ ions overlapped with a broad band attributed to the molecular electrophosphorescence (EP) from the triplet-singlet (T-1-->S-0) transition from the TTA ligand. The intensity ratio of the peaks is determined by the bias voltage applied to the OLED and this fact, together with the ligand electrophosphorescence, allows fabrication of a voltage-tunable color light source. (C) 2004 Elsevier B.V. All rights reserved.