Synthesis, photoluminescence features with intramolecular energy transfer and Judd–Ofelt analysis of highly efficient europium(III) complexes

The luminescent binary and ternary europium(III) complexes were prepared by employing ethyl-(3-fluorobenzoyl) acetate (m-EFBA) as primary ligand and neocuproine (neo), bathophenanthroline (batho), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy) as secondary ligands. The synthesized complexes Eu(m-EFBA)₃·(H₂O)₂ (C1), Eu(m-EFBA)₃·neo (C2), Eu(m-EFBA)₃·batho (C3), Eu(m-EFBA)₃·phen (C4), Eu(m-EFBA)₃·bipy (C5) were characterized by the means of elemental analysis (C, H and N), nuclear magnetic resonance spectroscopy (¹H-NMR), infrared spectroscopy (IR), thermogravimetric analysis (TG/DTG), UV–visible and photoluminescence (PL) spectroscopy. The photoluminescence spectra of complexes exhibit the characteristic emission band at 613 nm assigned to hypersensitive ⁵D₀ → ⁷F₂ transition, responsible for the red color emission of complexes. The higher photoluminescence intensity of ternary europium(III) complexes C2–C5 as compared to binary complex C1, suggest that ancillary ligands neo, batho, phen and bipy enhance the process of sensitization from ligand (m-EFBA) to europium(III) ion. The luminescence decay time and quantum efficiencies of the complexes were determined to estimate the efficiency of energy transfer from ligand to metal ion. In addition, the Judd–Ofelt intensity parameters (Ω₂, Ω₄) were calculated from the emission intensities of ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₄ transitions of europium(III) ion respectively. The intramolecular energy transfer mechanism of the complexes were also investigated and results indicate that the ligand (m-EFBA) and ancillary ligands effectively transfer the energy to that of Eu(III) ion.