Luminescent properties of soft lanthanide metal-organic frameworks at high pressures: Implication for pressure sensor and pressure transmitting media simultaneously

• The ratiometric fluorescence sensing function is preserved in degraded MOFs. • The pressure-induced softening effect is discovered in the MOFs. • These degraded MOFs can be severe as both pressure transmitting medium and pressure scale simultaneously. Metal-organic-frameworks (MOFs), consisting of various and flexible metal ions/clusters and organic ligands, represent an important class of multifunction materials. However, some MOFs suffer from their instability for specific applications. In the present study, the luminescent properties and structure evolution of lanthanide-based MOFs (Eu-MOF and Tb-MOF) are systemically investigated up to ∼ 15 GPa. The luminescence of Eu-MOF and Tb-MOF, originating from the energy transfer process of Eu 3+ and Tb 3+ ions, show linear red shifts upon compression, holding a promise for pressure sensor application. The underlying mechanism is that the luminescence of Eu 3+ and Tb 3+ ions are mostly sensitive to the local environment rather than the symmetry of the framework. Thus, the luminescent properties of the Eu-MOF and Tb-MOF are preserved in their degraded counterparts, even undergoing the triclinic-to-triclinic isostructure phase transition at ∼ 4 GPa. Furthermore, their compressibility is comparable with the typical solid pressure transmitting medium (PTM) of NaCl. In addition, a pressure-induced softening effect is discovered in the degraded MOFs, which further alleviates the indispensable hardening effect of PTM at high pressures. Consequently, these soft degraded MOFs can serve as PTM and pressure sensors simultaneously, which will facilitate the diamond anvil cell experiment in the future.