We studied carrier recombination dynamics in CdSe nanocrystals, CdSe nanorods, Mn-doped CdS nanocrystals, and carbon nanotubes using femtosecond pump-probe spectroscopy. Auger recombination in nanocrystals and nanorods occurs due to three-carrier collisions, while that in carbon nanotubes occurs due to two-exciton collisions. We found that the Auger coefficient depends strongly on the nanocrystal size. In Mn-doped CdS nanocrystals, we observed that the decay time is almost independent of the excitation intensity. This indicates that the Auger recombination process is controlled by doping of Mn ions into CdS nanocrystals. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim