Voltage-dependent recombination region movement in organic light-emitting diodes (OLEDs) based on a europium complex-doped polymer

The europium complex Eu (bphse)(3)(ClO4)(3) was dissolved in chloroform and doped into poly(N-vinylcarbazole) (PVK). The doped polymer was sandwiched between a hole transport layer of poly(p-phenylene vinylene) (PPV) and an e lectron transport layer tris (8-hydroxy quinoline) aluminium (Alq(3)) by sp in coating, to form a three-layer organic light-emitting device. The observ ed electroluminescence of the devices varied from green to orange with appl ied voltage and the different electroluminescence (EL) spectra were recorde d. The results of our experiments indicate that the recombination region of holes and electrons in the devices moves from the Alq(3) layer towards the PVK :Eu layer with increasing applied electric field. (C) 2000 Elsevier Sc ience B.V. All rights reserved.