Novel Stoichiometrically Erbium−Ytterbium Cocrystalline Complex Exhibiting Enhanced Near-Infrared Luminescence

Three β-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 RC,DA, obtained from the Förster 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.