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 Er1.4Yb0.6(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 Er1.4Yb0.6(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 Er1.4Yb0.6(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 A) 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.