all core NCs, three PL lifetimes s1 (5–12 ns), s2 (40–90 ns), and s3 (204–362 ns) were observed (Fig. 4a; Table 3). Considering s3 is in the range of hundreds of nanoseconds and all PL emission spectra have broad peaks, we also attribute s3 to the donor– acceptor transition. In addition, upon comparing A1 and A2 parameters for each pair of a core and its corresponding core–shell (Table 3), both parameters are decreased after ZnS shell growth. The ZnS shell growth minimizes surface defects and may be involved in core etching (or core size reduction) due to exchange of copper or indium in the core with Zn ions from Zn precursor (Park and Kim 2011; Trizio et al. 2012). It is reasonable to associate the decrease of A1 and A2 with the minimization of surface defects and intrinsic defects. In other words, s1 and s2 indicating two energy states between the conduction band and the valence band of NCs for electron–hole recombination could be related to intrinsic and surface defects. However, it may not be appropriate to correlate which lifetime parameter to which type of defects, because both intrinsic and surface defects could contribute to both energy states.