Ionic liquid as plasticizer for europium(III)-doped luminescent poly(methyl methacrylate) films

Flexible luminescent polymer films were obtained by doping europium(III) complexes in blends of poly(methyl methacrylate) (PMMA) and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N]. Different europium(III) complexes have been incorporated in the polymer/ionic liquid matrix: [C6mim][Eu(nta)4], [C6mim][Eu(tta)4], [Eu(tta)3(phen)] and [choline]3[Eu(dpa)3], where nta is 2-naphthoyltrifluoroacetonate, tta is 2-thenoyltrifluoroacetonate, phen is 1,10-phenanthroline, dpa is 2,6-pyridinedicarboxylate (dipicolinate) and choline is the 2-hydroxyethyltrimethyl ammonium cation. Bright red photoluminescence was observed for all the films upon irradiation with ultraviolet radiation. The luminescent films have been investigated by high-resolution steady-state luminescence spectroscopy and by time-resolved measurements. The polymer films doped with β-diketonate complexes are characterized by a very intense 5D0 → 7F2 transition (up to 15 times more intense than the 5D0 → 7F1) transition, whereas a marked feature of the PMMA films doped with [choline]3[Eu(dpa)3] is the long lifetime of the 5D0 excited state (1.8 ms).