Novel stoichiometrically erbium-ytterbium cocrystalline complex exhibiting enhanced near-infrared luminescence

Three beta-diketonate complexes of erbium and ytterbium, Er(HFA)(3)(TPPO)(3), Yb(HFA)(3)(TPPO)(3), and Er1/2Yb1/2(HFA)(3)(TPPO)(2) (HFA = hexafluoroacetylacetonate, TPPO = triphenylphosphine oxide) are synthesized and structurally characterized, and their luminescent properties are examined in detail. Compared with monometallic complexes Er(HFA)(3)(TPPO)(3) and Er(HFA)(3)(TPPO)(3), the stoichiometrically Er-Yb cocrystalline complex Er1/2Yb1/2(HFA)(3)(TPPO)(2) exhibits special indirect near-infrared (NIR) luminescence with the acceptor and sensitizer(donor) coexisting in a single crystal. Of interest is that the NIR luminescence of the erbium ion in Er1/2Yb1/2(HFA)(3)(TPPO)(2) is significantly enhanced because of the coexistence of the ytterbium ion through the energy-transfer between the ytterbium and erbium ions. The estimated donor-acceptor energy-transfer critical radii R-C,R-DA, obtained from the Forster model, are in good agreement with those determined from the single X-ray crystal structure, confirming the dipole-dipole character for such a Yb-Er energy-transfer process.