Near‐IR to Near‐IR Upconversion Luminescence in Molecular Chromium Ytterbium Salts

Upconversion photoluminescence in hetero‐oligonuclear metal complex architectures featuring organic ligands is an interesting but still rarely observed phenomenon, despite its great potential from a basic research and application perspective. In this context, a new photonic material consisting of molecular chromium(III) and ytterbium(III) complex ions was developed that exhibits excitation‐power density‐dependent cooperative sensitization of the chromium‐centered (2)E/(2)T(1) phosphorescence at approximately 775 nm after excitation of the ytterbium band (2)F(7/2)→(2)F(5/2) at approximately 980 nm in the solid state at ambient temperature. The upconversion process is insensitive to atmospheric oxygen and can be observed in the presence of water molecules in the crystal lattice.