Luminescent mechanism analyzing and metal-ion sensing of Eu(III)-organic ligands complex doped gelatin-based films and hydrogels

•Composite films were prepared by doping Eu complexes into gelatins.•The mechanisms for the different luminescence of composite films were clarified.•Luminescent gelatin-based hydrogels were prepared for sensing metal ions.•The detection limit of Eu(TTA)3phen@gh for Fe3+ was about 1.15 μM.