OPTICAL STUDIES OF IV-VI QUANTUM DOTS

PbS microcrystallites show strong quantum confinement effects on accou nt of the fact that the particle size is much smaller than the exciton Bohr radius, leading to large blue shifts of the optical absorption e dge and the transverse optical phonon frequencies. In addition, femtos econd pump-probe experiments find a transient absorption with tetraber tz oscillatory behavior, due to vibrational quantum beats. The frequen cy of the tetrahertz response agrees with the fundamental infrared abs orption of the PbS microcrystallites, suggesting that the vibrational mode to which the photoexcited carriers couple is a transverse optical phonon.