Heterometallic Europium(III)-Lutetium(III) Terephthalates as Bright Luminescent Antenna MOFs.

A new series of luminescent heterometallic europium(III)-lutetium(III) terephthalate metal-organic frameworks, namely (Eu x Lu 1-x ) 2 bdc 3 ·nH 2 O, was synthesized using a direct reaction in a water solution. At the Eu 3+ concentration of 1-40 at %, the MOFs were formed as a binary mixture of the (Eu x Lu 1-x ) 2 bdc 3 and (Eu x Lu 1-x ) 2 bdc 3 ·4H 2 O crystalline phases, where the Ln 2 bdc 3 ·4H 2 O crystalline phase was enriched by europium(III) ions. At an Eu 3+ concentration of more than 40 at %, only one crystalline phase was formed: (Eu x Lu 1-x ) 2 bdc 3 ·4H 2 O. All MOFs containing Eu 3+ exhibited sensitization of bright Eu 3+ -centered luminescence upon the 280 nm excitation into a 1 ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu 3+ 5 D 0 - 7 F J (J = 0-4) significantly depended on the Eu 3+ concentration. The luminescence quantum yield of Eu 3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu 3+ due to the absence of Eu-Eu energy migration and the presence of the Ln 2 bdc 3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln 2 bdc 3 ·4H 2 O.