Efficient Sensitized Luminescence of Binuclear Ln(III) Complexes Based on a Chelating Bis-Carbacylamidophosphate.

Binuclear rare earth complexes Ln2L3phen2 (LnIII = NdIII, SmIII, EuIII, TbIII, DyIII, YbIII and YIII) with bis-CAPh type ligand - tetramethyl N,N'-(2,2,3,3,4,4-hexafluoro-1,5-dioxopentane-1,5-diyl)bis(phosphoramidate) (H2L) and 1,10-phenanthroline (phen) were synthesized and characterized by elemental analysis, IR, NMR, absorption and luminescence spectroscopy. Luminescence measurements were performed for all the complexes in solid state and for the EuIII, TbIII and YIII complexes - in solution in DMSO as well. The effective energy transfer from organic ligands to LnIII ions strongly sensitizes the LnIII ions emission and under excitation by UV light, the complexes exhibited bright characteristic emission of lanthanide metal centers. It was found that the energy level of the ligands lowest triplet state in the complexes matches better to resonance level of EuIII rather than TbIII ion. Depending on temperature the emission decay times of solid europium and terbium complexes were in the range of 1.5-2.0 ms. In solid state at room temperature the EuIII complex possess intense luminescence with very high intrinsic quantum yield 91% and decay time equal 1.88 ms.