Syntheses, crystal structures and near-infrared luminescent properties of holmium (Ho) and praseodymium (Pr) ternary complexes

A series of near-infrared (NIR) luminescent complexes Ho(dbm)3L and Pr(dbm)3L [where dbm = dibenzoylmethane; L = 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), or triphenyl phosphate oxide (TPPO)] were synthesized. Their elemental analyses, crystal structures, fluorescence spectra and luminescent lifetimes were successfully investigated. After ligand-mediated excitation of the complexes, they all show the characteristic NIR luminescence of the corresponding Ln3+ ions (Ln = Ho, Pr), which can be attributed to efficient energy transfer from the ligands to the central Ln3+ ions, an antenna effect.