Luminescence enhancement of Eu3+-doped poly(acrylic acid) using 1,10-phenanthroline as antenna ligand

This work reports on the photoluminescence enhancement of Eu3+-doped poly(acrylic acid) using 1,10-phenanthroline as antenna ligand. The polymeric material was synthesized by polymerization in aqueous solution of the monomer partially neutralized with Eu2O3, containing 1,10-phenanthroline, and using potassium persulfate as initiator. The monomer modification and the coordination of antenna ligand to the Eu3+ ions were confirmed by 1H-NMR. The doped polymer was characterized by luminescence spectroscopy. The excitation spectra show clear evidence of the coordination between the Eu3+ ions and the 1,10-phenanthroline ligands in the polymer matrix. On the other hand, the emission spectra show an inhomogeneous broadening and, together with the relative intensity of the 5D0→7F1,2 transitions of Eu3+, indicate that the dopant ions are uniformly distributed in low symmetry coordination sites. Besides, an enhancement in the intensity of the Eu3+ characteristic red emission by 1,10-phenanthroline addition is observed, and it is due to the antenna effect of the ligand, which acts as a sensitizer of the Eu3+ ions. An estimation of the increasing luminescence efficiency is presented.