Low threshold amplified spontaneous emission and Auger recombination suppression in giant nanocrystal quantum dots

Nanocrystals quantum dots (NQDs) are attractive materials for various light-emitting applications including optical amplification and lasing. A complication associated with the multiexcitonic nature of light amplification is NQDs is the picosecond optical-gain decay induced by nonradiative Auger recombination, in which one exciton recombines by transferring the energy to the other. Here, we present new results on a novel type of nanocrystals dubbed ``giant'' quantum dots (g-NQDs). These g-NQDs comprise an emitting core particle of CdSe overcoated with a thick shell (up to 20 monolayers) of wider-gap CdS. We report that biexciton and gain lifetimes are greatly augmented and the ASE threshold drops down to just a few $\mu $J/cm2. We explain this result by a significant increase in the absorption cross-section of g-NQDs compared to traditional nanocrystals and lengthening of biexciton lifetimes. We also observe other unusual optical-gain behaviors for these structures such as multi-band ASE, the spectra spectral range of optical amplification extends over more than 500 meV. These results demonstrate that g-NQDs are very promising materials for applications in practical lasing technologies.