Electronic structure and photoexcited-carrier dynamics in nanometer-size CdSe clusters

We use transient optical hole burning and photoluminescence to investigate the static and dynamic electronic properties of 32- CdSe quantum dots. We observe a number of discrete electronic transitions, resolve LO-phonon progressions, and obtain homogeneous linewidths and electron--LO-phonon couplings. We find that the band-gap luminescence is not from the exciton state, but from a surface trapped state. Rapid (160 fs) trapping into these surface states results in long-lived (10--100 ns) bleach and induced-absorption features in pump-probe experiments.