ABSTRACT
We measure the photoluminescence lifetime τ of excitons in colloidal PbSe nanocrystals (NCs) at low temperatures to 270 mK and in high magnetic fields to 15 T. For all NCs, τ increases sharply below 10 K but saturates by 500 mK. In contrast to the usual picture of well-separated "bright" and "dark" exciton states (found, e.g., in CdSe NCs), these dynamics fit remarkably well to a system having two exciton states with comparable--but small--oscillator strengths that are separated by only 300-900 µeV depending on NC size. Importantly, magnetic fields reduce τ below 10 K, consistent with field-induced mixing between the two states. Magnetic-circular dichroism studies reveal exciton g factors from 2-5, and magnetophotoluminescence shows >10% circularly polarized emission.
ABSTRACT
Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4 K) time-resolved PL measurements show a decay time of [Formula: see text] ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text] ns).
