Chapter 7 - Linear and nonlinear optical spectroscopy of semiconductor nanocrystals

Abstract

This chapter concentrates on optical nonlinearities observed at energies near the band edge. These nonlinearities are dominated by real photoexcitations (excitons and/or free carriers) and are often referred to as resonant nonlinearities. The magnitudes of these nonlinearities are much greater than for nonresonant ones associated with virtual transitions and observed in the transparency range of optical materials. The increase in the magnitude of the nonlinearity in the resonant case occurs at the expense of the nonlinearity relaxation time. Significant progress has been made in understanding the effects of carrier dynamics on the optical properties of NCs. Modern methods of fs spectroscopy allow direct observation of ultrafast energy relaxation, recombination, and dephasing processes. Time-resolved studies indicate an important role of surface (interface) states in carrier relaxation. Important issues about the effect of three-dimensional confinement on energy relaxation have been raised by theoretical and experimental studies of carrier intraband dynamics in strongly confined NCs. These studies indicate a significant role of energy-loss mechanisms, which are different from electron-phonon interactions. Important steps toward practical applications have been realized with studies of optical nonlinearities, optical gain, and lasing in NCs. Due to three-dimensional spatial confinement, the mechanisms for resonant band-edge optical nonlinearities in NCs are different from those in bulk materials.