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

Abstract The surface of Eu_0.3La_0.7F₃ 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 Eu_0.3La_0.7F₃@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 λ_exc = 396 nm (maximum of the Eu(III) ⁵L₆ ← ⁷F₀ 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 σ₂ = 9.4 ± 1.0 GM at 780 nm (σ₂ = 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.