Luminescence properties of mechanochemically synthesized lanthanide containing MIL-78 MOFs

Abstract

Three metal–organic framework (MOF) compounds, Ln_0.5Gd_0.5{C₆H₃(COO)₃}; Ln = Eu, Tb, and Dy with a MIL-78 structure, have been synthesized by a solvent-free mechanochemical method from stoichiometric mixtures of benzene 1,3,5-tricarboxylic acid, C₆H₃(COOH)₃, also known as trimesic acid, and the respective lanthanide carbonates, Ln₂(CO₃)₃·xH₂O, Ln = Eu, Gd, Tb and Dy. MIL-78 (Ln_0.5Gd_0.5) shows the characteristic red, green, and yellow luminescence of Eu³⁺, Tb³⁺, and Dy³⁺, respectively. Efficient intramolecular energy transfer from the ligand triplet state to the excited states of Ln³⁺ ions can be observed. The lifetimes and quantum yields of these compounds are studied and discussed in detail. Among the three compounds, the Tb³⁺ containing compound shows the longest lifetime and highest quantum yield due to a smaller contribution from non-radiative decay pathways and better matching of the lowest triplet energy level of the benzenetricarboxylate ligand and the resonance level of Tb³⁺.