“Giant” Cd Se/Cd S core/shell nanocrystals(NCs) were synthesized with thick Cd S shell(15 monolayers), and the x-ray diffraction(XRD) measurement indicates there is a zinc blende phase in the thick Cd S shell, whereas it transformed into wurtzite phase under 5 min radiation with a 400 nm, 594 μJ∕cm2femtosecond(fs) laser beam.The evolution of the NCs’ spontaneous emission under the fs laser radiation was recorded with a Hamamatsu streak camera. The as-synthesized NCs exhibit an amplified spontaneous emission(ASE) at 530 nm, which comes from a bulk-like Cd S shell due to the interfacial potential barrier, which could slow down the relaxation of holes from the shell to the core. After being annealed by an fs laser, the ASE of the g-NCs is transferred from a bulk-like Cd S shell to a quantum-confined Cd Se core because the phase transformation determined with the XRD measurement could remove the interfacial barrier. Besides the ASE at 643 nm, two shorter-wavelength ASE peaks at 589 and 541 nm, corresponding to optical transitions of the second(1P) and third(1D) electron quantization shells of the Cd Se core, also appear, thus indicating that Auger recombination is effectively suppressed. “Giant” Cd Se / Cd S core / shell nanocrystals (NCs) were synthesized with a thick Cd S shell (15 monolayers), and the x-ray diffraction (XRD) measurement shows there is a zinc blende phase in the thick Cd S shell, and it transformed into wurtzite phase under 5 min radiation with a 400 nm, 594 μJ / cm2femtosecond (fs) laser beam. The evolution of the NCs’ spontaneous emission under the fs laser radiation was recorded with a Hamamatsu streak camera. The as-synthesized NCs exhibit an amplified spontaneous emission (ASE) at 530 nm, which comes from a bulk-like Cd S shell due to the interfacial potential barrier, which could slow down the relaxation of holes from the shell to the core. annealed by an fs laser, the ASE of the g-NCs is transferred from a bulk-like Cd S shell to a quantum-confined Cd Se core as the phase transformation determined with the XRD measurement could remove the interfacial barrier. 643 nm, two shorter-wavelength ASE peaks at 589 an d 541 nm, corresponding to optical transitions of the second (1P) and third (1D) electron quantization shells of the Cd Se core, also appear, which indicates that Auger recombination is effectively suppressed.