metal - organic frameworks are crystalline porous materials that include metal ions linked together into periodic structures via organic ligands . mofs that contain lanthanide ions are a new class of visible and near - ir luminescent materials , suitable for a broad range of applications . for example , the mof framework afforded by 2 , 5 - dimethoxy - 1 , 4 - phenylene ) di - 2 , 1 - ethenediyl ] bis - carboxylate is associated with unusually long luminescence lifetimes . thus , a complex of this ligand with a lanthanide provides a sharp emission profile , coupled with a comparatively long signal lifetime , for an unusually high luminescence . more generally , lanthanide - mof systems exhibit several advantages that are ideal for barcoded materials , due to the photophysical attributes of lanthanide cations and the well - defined organization of the mof structure .