Cooperative Sensitization Upconversion in Ytterbium(III)‐based Eosin Lake Pigments

Materials based on organic chromophores and lanthanides able to transform low‐energy photons, specifically near‐infrared (NIR) photons, into higher energy photons to eventually lead to long‐lived sensitized emission of the dye are highly desirable. Cooperative sensitization (CS) upconversion has only been accomplished for lanthanide‐based clusters. We used here eosin Y (EOS) dianion and Yb3+ (EOS‐Yb), and demonstrate the efficient CS emission of the dye after NIR excitation. Remarkably, the EOS dianion emission exhibits a nearly linear dependence on the EOS‐Yb concentration and a quadratic dependence on the laser power density. The emission is non‐sensitive to oxygen and its lifetime lasts about 1.76 ms and 12 ms in DMSO and DMSO‐d6, respectively. Moreover, the effect of temperature (293‒363 K range) on the EOS‐Yb 1H‐NMR shifts demonstrates the reversible dynamic nature of the material.