A highly efficient OLED based on terbium complexes

A neutral ligand 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphineoxide)-carbazole (DPPOC) and its complex Tb(PMIP)(3)DPPOC (A, where PMIP stands for 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) were synthesized. DPPOC has a suitable lowest triplet energy level (24,691 cm(-1)) for the sensitization of Tb(Ill) (D-5(4): 20,400 cm(-1)) and a significantly higher thermal stability (glass transition temperature 137 degrees C) compared with the familiar ligand triphenylphosphine oxide (TPPO). Experiments revealed that the emission layer of the Tb(PMIP)(3)DPPOC film could be prepared by vacuum co-deposition of the complex Tb(PMIP)(3)(H2O)(2) (B) and DPPOC (molar ratio = 1:1). The electroluminescent (EL) device ITO/N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-diphenyl-4,4'-diamine (NPB; 10nm)/Tb(PMIP)(3) (20 nm)/co-deposited Tb(PMIP)(3)DPPOC (30 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP: 10nm)/tris(8-hydroxyquinoline) (AlQ; 20 nm)/Mg0.9Ag0.1 (200 nm)/Ag (80 nm) exhibited pure emission from terbium ions, even at the highest current density. The highest efficiency obtained was 16.1 lm W-1, 36.0 cd A(-1) at 6 V. At a practical brightness of 119 cd m(-2) (11V) the efficiency remained above 4.5 lm W-1, 15.7 cd A(-1). These values are a significant improvement over the previously reported Tb(PMIP)(3)(TPPO)(2) (C). (C) 2009 Elsevier B.V. All rights reserved.