Optical Upconversion in Mononuclear Lanthanide Co-Crystal Assemblies.

In this work, we developed two kinds of co-crystal assemblies systems, consisting of discrete mononuclear Yb 3+ and Er 3+ and mononuclear Yb 3+ and Pr 3+ , which can achieve Er 3+ and Pr 3+ upconversion luminescence, respectively, by Yb 3+ sensitization under 980 nm excitation. The structure and composition of two co-crystal assemblies were determined by single crystal X-ray diffraction. By investigation of the series of two assemblies, respectively, it is found that the strongest upconversion luminescence is both obtained when the molar ratio of Yb 3+ and Ln 3+ (Ln=Er or Pr) is 1 : 1. The energy transfer mechanism of Er 3+ assemblies is determined as energy transfer upconversion, while that of Pr 3+ assemblies is determined as energy transfer upconversion and cooperative sensitization upconversion. This is the first example of Pr 3+ upconversion luminescence at the molecular dimension at room temperature, which enriches the research in the field of upconversion luminescence with lanthanide complexes.