Crystal structure and near-infrared luminescence properties of novel binuclear erbium and erbium–ytterbium cocrystalline complexes

Abstract

Three binuclear complexes of erbium and ytterbium, Er₂(Ba)₆(Phen)₂, Yb₂(Ba)₆(Phen)₂ and Er_1.4Yb_0.6(Ba)₆(Phen)₂ (Ba = benzoate, Phen = 1,10-phenanthroline), were synthesized and structurally characterized, and their luminescent properties examined in detail. Compared with the binuclear complex Er₂(Ba)₆(Phen)₂, the NIR luminescence of the erbium ion in Er_1.4Yb_0.6(Ba)₆(Phen)₂ is enhanced because of the coexistence of the ytterbium ion through an ytterbium-to-erbium energy transfer process. The full width at half maximum, centered at 1535 nm in the emission spectrum of Er_1.4Yb_0.6(Ba)₆(Phen)₂, is 108 nm, excited at 975 nm, which has potential to enable a wide-gain bandwidth for optical amplification. The X-ray single crystal structure confirms that this is an excellent binuclear complex model with a short metal-to-metal distance (about 4 Å) to facilitate the intramolecular (not intermolecular) Yb–Er energy transfer process. ESI-MS confirmed the molecules Er₂(Ba)₆(Phen)₂, Yb₂(Ba)₆(Phen)₂ and ErYb(Ba)₆(Phen)₂ exist in solution.