Metal organic frameworks MOFs also
Metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs) have attracted many chemists’ interest owing to their fascinating structural topologies and potentials in functional applications , such as molecular filter, gas storage  and , energy storage  and luminescent sensor  and . Among the various kinds of MOFs, Lanthanide metal-organic frameworks (Ln-MOFs) as sensing materials for pollutant detection, such as poisonous gases, organic solvents, and heavy metals, have recently received increasing attention because of the advantages of short response time and high sensitivity toward specific analytes . Compared with transition metals, lanthanide MOFs as luminescent sensor are especially attractive due to their excellent luminescent properties originating from the 4f electrons of lanthanide, such as large Stokes shifts, extremely sharp emission and long lifetime  and . However, as we know that the f-f transitions of lanthanide ions are parity-forbidden, which results in very low CCG-1423 coefficients. Efficient “antenna” organic ligands coordinated to lanthanide ions as energy donors can provide sufficient energy to induce intense characteristic emissions of lanthanide ions . Considering their intense visible luminescence, Ln-MOFs could be ideal candidates as luminescent sensing materials. In particular, Eu(III) MOFs and Tb(III) MOFs with carboxylic organic ligands are considered most useful in practical application due to their visible red/green characteristic luminescence as well as long luminescence lifetimes . Until now, various types of lanthanide metal-organic frameworks in sensing of metal ions ,  and , anions , gas molecules  and , nitro explosives ,  and , small molecules , , , ,  and  and temperature  have been realized and reported. However, most of them are brittle crystals or loose powders synthesized by hydrothermal/solvothermal methods and require specific solvent condition to detect analyte, which strictly limited their in-field application. Although in the form of solution or suspension-state is helpful for qualitative analysis, but they are difficult to operate as practical in-field sensors unless processed into applicable configurations such as thin film .