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 Eu 0.3 La 0.7 F 3 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 Eu 0.3 La 0.7 F 3 @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 λ exc = 396 nm (maximum of the Eu(III) 5 L 6 ← 7 F 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 σ 2 = 9.4 ± 1.0 GM at 780 nm (σ 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.