Exciton Relaxation in PbSe Nanorods

Measurements of the picosecond-time-scale dynamics of photoexcited electrons in PbSe nanorods are reported. The intraband (1Π → 1Σ) relaxation occurs with a time constant of ~500 fs, which corresponds to a fast energy-relaxation rate of ~0.6 eV/ps. The biexciton lifetime in PbSe nanorods is significantly (3-4 times) longer than the lifetime of PbSe quantum dots with the same energy gap, roughly as expected considering the increased volume. The multiexciton lifetimes of PbSe nanorods scale as expected for a bimolecular recombination mechanism. Implications of the observed relaxations will be discussed.