Ultrafast dynamics of inter- and intraband transitions in semiconductor nanocrystals: Implications for quantum-dot lasers

Application of femtosecond transient absorption in the visible and near-IR Spectral ranges and time-resolved photoluminescence allows us to separate e lectron and hole relaxation paths and to map the structure bf interband and intraband optical transitions in CdSe and CdS nanocrystals (NC's) with a w ide range of surface properties. In contrast to electron relaxation, which is controlled by NC surface passivation, depopulation of hole quantized sta tes is extremely fast (sub-ps-to-ps time scales) in all types samples, inde pendent of NC surface treatment (including NC's overcoated with a ZnS layer ). Our results suggest that ultrafast hole dynamics are not due to trapping at localized surface defects such as a vacancy, but rather arise from rela xation into intrinsic NC states or intrinsically unpassivated interface sta tes. [S0163-1829(99)51228-9].