Brightly Luminescent (Tb(x)Lu(1−x))(2)bdc(3)·nH(2)O MOFs: Effect of Synthesis Conditions on Structure and Luminescent Properties

Luminescent, heterometallic terbium(III)–lutetium(III) terephthalate metal-organic frameworks (MOFs) were synthesized via direct reaction between aqueous solutions of disodium terephthalate and nitrates of corresponding lanthanides by using two methods: synthesis from diluted and concentrated solutions. For (Tb(x)Lu(1−x))(2)bdc(3)·nH(2)O MOFs (bdc = 1,4-benzenedicarboxylate) containing more than 30 at. % of Tb(3+), only one crystalline phase was formed: Ln(2)bdc(3)·4H(2)O. At lower Tb(3+) concentrations, MOFs crystallized as the mixture of Ln(2)bdc(3)·4H(2)O and Ln(2)bdc(3)·10H(2)O (diluted solutions) or Ln(2)bdc(3) (concentrated solutions). All synthesized samples that contained Tb(3+) ions demonstrated bright green luminescence upon excitation into the (1)ππ* excited state of terephthalate ions. The photoluminescence quantum yields (PLQY) of the compounds corresponding to the Ln(2)bdc(3) crystalline phase were significantly larger than for Ln(2)bdc(3)·4H(2)O and Ln(2)bdc(3)·10H(2)O phases due to absence of quenching from water molecules possessing high-energy O-H vibrational modes. One of the synthesized materials, namely, (Tb(0.1)Lu(0.9))(2)bdc(3)·1.4H(2)O, had one of the highest PLQY among Tb-based MOFs, 95%.