Doping metal-organic framework with a series of europium-antenna cations: Obviously improved spectral response for O2 gas via long-range energy roll-back procedure

Abstract In this paper, a lanthanide cation, Eu(III), was firstly coordinated with a series of organic antenna ligands and then doped into bio-MOF-1 via cation exchange for O2 optical sensing. These organic ligands were supposed to increase dynamic collision probability between O2 molecules and excited probe molecules, so that sensitivity could be increased and response time could be decreased. These composite samples were firstly identified using SEM, XRD, N2 adsorption/desorption and ICP measurement to confirm their microstructure. Then their absorption spectra, emission spectra and emission lifetimes were discussed. It was found that these composite samples showed long emission lifetime up to 595 μs, which ensured enough time for O2 collision. Their O2 sensing performance was discussed via their emission spectra under increasing O2 concentrations. Linear sensing curves were observed for all samples. It was found that a large conjugation plane improved sensitivity and decreased response time since this large conjugation plane increased dynamic collision probability. The sensing mechanism was confirmed as the O2 quenching on long-range energy roll-back from ligand triplet state to bio-MOF-1. The highest sensitivity and the shortest response time were obtained as 6.96, three times higher than literature values, and 12 seconds, respectively.