The complexation of the lanthanide Eu(III) and the actinides Cm(III) and Am(III) by N-3(-) was investigated by application of time-resolved laser fluorescence spectroscopy (TRLFS) and X-ray absorption spectroscopy (XAFS) in the ionic liquid solution Of C(4)mimTf(2)N (1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide). TRLFS, measurements show that the interaction of azide with Eu(CF3SO3)(3) and Eu(ClO4)(3) results in both dynamic luminescence quenching by collisional encounters of N-3(-) with Eu(III) and static luminescence quenching by inner-sphere complexation of Eu(III) by N-3(-). Hereby, the complexation of Eu-triflate by azide starts at a lower N-3(-) concentration as compared to the perchlorate salt. The authors ascribe this phenomenon to a stronger bonding Of ClO4- toward the metal ion than triflate, as well as to a stronger electrostatic repulsion of N-3(-) by the perchlorate ligand. In both actinide samples (Cm(ClO4)(3), Am(ClO4)(3)), the complexation with azide exhibits a clear kinetic hindrance. Nevertheless, mixed actinide-perchlorate-azide complexes are formed after several days in C(4)mimTf(2)N. The different reaction kinetics for the Ln- and An-complexation by azide may provide the opportunity for an effective separation of lanthanides from actinides in the nuclear fuel cycle by the use of N-based extractants in ionic liquid solution.