Mechano-thermochemical synthesis of rare-earth metal–organic frameworks with solvent-free coordination for visible and near-infrared emission

Abstract

Rare earth metal–organic frameworks are considered as one emerging class of materials with extraordinary photoluminescence functions. However, the coordination of solvent molecules, due to their intrinsic high coordination numbers, leads to non-radiative multiphoton relaxation, which impairs their luminescence. Therefore, in this contribution, we propose a mechano-thermochemical method as a universal approach towards achieving solvent-free rare-earth metal–organic frameworks. A novel series of solvent-free rare-earth metal–organic frameworks named TJU-66 has been synthesised, exhibiting a (3,6)-c net zxc topology with a rare 6,6 coordination shape, and presenting high stabilities. Isostructural mixed metal–organic frameworks have been created by doping with rare earth ions to further improve the luminescence, reflected in the extremely high quantum yields and fluorescence lifetimes. It is worth noting that the wavelengths of different mixed metal–organic frameworks cover the whole region of visible and near-infrared light. Furthermore, by doping with Sc, the fluorescence lifetime of the Yb-based MOFs could be greatly improved up to 43.1 μs, which is so far the highest value of Yb-based MOFs. Our series of TJU-66 materials has not only replenished the existing library of luminescent metal–organic frameworks, but also, the mechano-thermochemical method highlighted in this work may provide a general method for the future development of solvent-free materials with exclusive functions.