Upconversion Luminescence in Mononuclear Yb/Sm Co-crystal Assemblies at Room Temperature.

Metal-based upconversion luminescence transforming high-energy photons into low-energy photons is an attractive anti-Stokes shift process for fundamental research and promising applications. In this work, we developed the upconversion luminescence in co-crystal assemblies consisting of discrete mononuclear Yb and Sm complexes. The characteristic visible emissions of Sm were observed under the excitation of absorption band of Yb at 980 nm. A series of co-crystal assemblies were investigated based on mononuclear Yb and Sm complexes, and the strongest luminescence was obtained when the molar concentration between Yb and Sm is equivalent. The crystal structure was fully characterized by the single crystal X-ray diffraction and upconverting energy transfer mechanisms were verified as cooperative sensitization upconversion and energy transfer upconversion. This is the first example of Sm -based upconverting luminescence in discrete lanthanide complexes which present as co-crystal assemblies at room temperature.