Color-Tunable Luminescence of Eu-Doped LaF₃ Particles Sensitized by d-f Energy Transfer from a Two-Photon Absorbing Ir(III) Complex

The surface of Eu0.3La0.7F3 submicron particles is functionalized with a blue-emitting Ir(III) complex (1) specifically designed to coordinate lanthanide(III) ions efficiently through a carboxylic unit. In this Eu0.3La0.7F3@1 composite, the Ir(III) complexes are randomly coordinated to either superficial La(III) ions or Eu(III) ions (Ir-La-surface and Ir-Eu-surface pairs, respectively) and its color emission, a balance between blue (Ir-based) and red (Eu-based) light, can be tuned as a function of the excitation wavelength. Irradiation at the maximum of the excitation band in 1 promotes blue emission from Ir-La-surface pairs and red emission from Eu-surface ions sensitized by Ir -> Eu-surface energy transfer (EnT). At lambda(exc) = 396 nm (maximum of the Eu(III) L-5(6) <- F-7(0) absorption band) the red emission from inner Eu(III) ions becomes dominant. Excitation of 1 can also be achieved by two photon-absorption (TPA) since this complex has a moderate cross-section of sigma(2) = 9.4 +/- 1.0 GM at 780 nm (sigma(2) = 5.8 +/- 0.6 GM at 800 nm). Phosphorescence lifetime imaging (PLIM) allows the emission of individual particles to be visualized and the Ir-, Eu-surface-, and Eu-core-based emissions can be distinguished due to the significant differences in their respective emission lifetimes.