Dual visible and near-infrared luminescence in mononuclear macrocyclic erbium(III) complexes ligand and metal centred excitation.

Considering the structural design of some of the scarce molecular-based Er-centred emitters in the literature, we explored the optical properties of three Er hexaazamacrocyclic complexes, namely Er-EDA (1), Er-OPDA(2) and Er-DAP(3). The macrocyclic ligands in these complexes differ in the lateral spacers, and are derived from 2,6-pyridine-dicarbaldehyde and ethylenediamine (EDA), -phenylenediamine (OPDA) or 1,3-diaminopropane (DAP). Upon ligand-centred excitation, the bluish-green and green emissions of the Er ion were detected only for the complexes containing macrocycles with aliphatic spacers (1 and 3), which evidenced that these ligands can sensitize the Er luminescence.