QUANTUM BEATS OF CONFINED EXCITONS IN CUCL NANOCRYSTALS

We have performed femtosccond degenerate four-wave-mixing (DFWM) to in vestigate coherent transient phenomena in CuCl nanocrystals. We presen t observation of quantum coherence of weakly confined excitons in nano crystals through quantum beats in the spectrally resolved signal of DF WM. In large nanocrystals with a mean radius R of 220 Angstrom, the qu antum beat between the sublevels of confined excitons is observed. In small nanocrystals with R = 40 Angstrom, we observe the quantum beat b etween the confined exciton and its optical phonon side band. These re sults suggest that the coupling of confined excitons to optical phonon s becomes stronger for the smaller sizes. In the decay behavior of coh erence, the two-component decay is observed, and the fast and slow com ponents are attributed to the homogeneous width of the phonon side ban d and that of zero-phonon band of the confined exciton transition: res pectively. (C) 1998 Elsevier Science B.V. All rights reserved.