Synthesis, Structure, Photoluminescence, and Electroluminescence of Four Europium Complexes: Fabrication of Pure Red Organic Light-Emitting Diodes from Europium Complexes

چکیده مقاله

Four novel europium complexes were prepared by reacting europium(III) thenoyltrifluoroacetonate trihydrate with new tridentate ligands based on dipyrazolyl triazine and utilized as emitting materials in electroluminescent devices. The complexes were characterized by elemental analysis, FT-IR spectroscopy, UV-vis spectrophotometery, and 1H NMR spectroscopy. The coordinated ligands serve as light-harvesting chromophores in the complexes with absorption maxima in the range of 334-402 nm [ε= (8.9-81.4) × 103 M-1 cm-1]. The ligands efficiently sensitize europium luminescence with maximum quantum yield 〖(Ԛ〗_L^Eu) and observed lifetime (τobs) values of 34% and 600 µs in the solid state and 35% and 528 µs in toluene, respectively. The radiative lifetimes of Eu (5D0) are in the range of 1170-1281 µs and the ligand-to-metal energy transfer efficiency (ηsens) is in the range of 71-92% for those complexes in the solid state and 68-97% for those in solution state. Additionally, organic light emitting diodes (OLEDs) with europium(III) complexes, which exhibited pure red emission, were fabricated. It is shown that by modifying the [Eu(tta)3.3H2O] molecule with ancillary ligands, one can change and control its electroluminescence (EL) spectra along with its electrical properties, such as the current-voltage (J-V) characteristics of OLED devices based on [Eu(tta)3(L)]. The best OLED presented a maximum luminance of 3156 cd/m2 and a maximum efficiency of 0.7 cd/A at an applied voltage of 8 V.