Three metal-organic framework (MOF) compounds, Ln(0.6) Gd-0.(6) {C6H (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, Ln(2)(CO3)(3)center dot xH(2)O, Ln = Eu, Gd, Tb and Dy. MIL-78 (Ln(0.5)Gd(0.)(6)) 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 Ln(3+) 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+.