Bright red electroluminescent devices using novel second-ligand-contained europium complexes as emitting layers

With two novel second ligands, 2-(2-pyridyl)benzimidazole (HPBM) and 1-ethyl-2-(2-pyridyl)benzimidazole (EPBM), two europium complexes, Eu(DBM)3HPBM and Eu(DBM)3EPBM (DBM = dibenzoylmethanato), were prepared and used as emitting materials in organic electroluminescent (EL) devices. The devices with the structures ITO/TPD/Eu(DBM)3HPBM (or Eu(DBM)3EPBM)/Al and ITO/TPD/Eu(DBM)3EPBM/AlQ/Al emit red light originating from the europium complexes. The EL luminance of Eu(DBM)3EPBM is much higher than that of Eu(DBM)3HPBM. A maximum luminance of 180 cd m−2 in the triple layered device of Eu(DBM)3EPBM was achieved at 18 V.