Cooperative Sensitization Upconversion in Solution Dispersions of Co-Crystal Assemblies of Mononuclear Yb and Eu Complexes.

Lanthanide upconversion luminescence in nanoparticles has prompted continuous breakthroughs in information storage, temperature sensing, and biomedical applications, among others. Achieving upconversion luminescence at the molecular scale is still a critical challenge in modern chemistry. In this work, we explored the upconversion luminescence of solution dispersions of co-crystals composed of discrete mononuclear Yb(DBM) Bpy and Eu(DBM) Bpy complexes (DBM: dibenzoylmethane, Bpy: 2,2'-bipyridine). The 613 nm emission of Eu was observed under excitation of Yb at 980 nm. From the series of molecular assemblies studied, the most intense luminescence was obtained for a 1 : 1 molar ratio of Yb  : Eu , resulting in a high quantum yield of 0.67 % at 2.1 W cm . The structure and energy transfer mechanism of the assemblies were fully characterized. This is the first example of an Eu -based upconverting system composed of two discrete mononuclear lanthanide complexes present as co-crystals in non-deuterated solution.