OPTICAL STUDIES OF IV-VI QUANTUM DOTS

PbS microcrystallites show strong quantum confinement effects on account of the fact that the particle size is much smaller than the exciton Bohr radius, leading to large blue shifts of the optical absorption edge and the transverse optical phonon frequencies. In addition, femtosecond pump-probe experiments find a transient absorption with tetrabertz oscillatory behavior, due to vibrational quantum beats. The frequency of the tetrahertz response agrees with the fundamental infrared absorption of the PbS microcrystallites, suggesting that the vibrational mode to which the photoexcited carriers couple is a transverse optical phonon.