Microcrystalline Luminescent (Eu 1-x Ln x ) 2 bdc 3 ·nH 2 O (Ln = La, Gd, Lu) Antenna MOFs: Effect of Dopant Content on Structure, Particle Morphology, and Luminescent Properties.

In this work, three series of micro-sized heterometallic europium-containing terephthalate MOFs, (Eu 1-x Ln x ) 2 bdc 3 ·nH 2 O (Ln = La, Gd, Lu), are synthesized via an ultrasound-assisted method in an aqueous medium. La 3+ and Gd 3+ -doped terephthalates are isostructural to Eu 2 bdc 3 ·4H 2 O. Lu 3+ -doped compounds are isostructural to Eu 2 bdc 3 ·4H 2 O with Lu contents lower than 95 at.%. The compounds that are isostructural to Lu 2 bdc 3 ·2.5H 2 O are formed at higher Lu 3+ concentrations for the (Eu 1-x Lu x ) 2 bdc 3 ·nH 2 O series. All materials consist of micrometer-sized particles. The particle shape is determined by the crystalline phase. All the synthesized samples demonstrate an "antenna" effect: a bright-red emission corresponding to the 5 D 0 - 7 F J transitions of Eu 3+ ions is observed upon 310 nm excitation into the singlet electronic excited state of terephthalate ions. The fine structure of the emission spectra is determined by the crystalline phase due to the different local symmetries of the Eu 3+ ions in the different kinds of crystalline structures. The photoluminescence quantum yield and 5 D 0 excited state lifetime of Eu 3+ are equal to 11 ± 2% and 0.44 ± 0.01 ms, respectively, for the Ln 2 bdc 3 ·4H 2 O structures. For the (Eu 1-x Lu x ) 2 bdc 3 ·2.5H 2 O compounds, significant increases in the photoluminescence quantum yield and 5 D 0 excited state lifetime of Eu 3+ are observed, reaching 23% and 1.62 ms, respectively.