Dephasing processes in II–VI quantum dots

The loss of phase coherence in II–VI quantum dots is investigated using experimental methods working both in the frequency and in the time domain. Femtosecond differential absorption experiments reveal narrow resonances at very early times after excitation and low excitation densities for CdSe quantum dots. A substructure is detected and explained by transitions from the series of confined hole states. By nondegenerate four‐wave mixing experiments (NDFWM) the dephasing time is determined for CdS quantum dots with radii larger than the Bohr radius. Temperature and excitation intensity dependent dephasing times between ≈ 20 fs and some 100 fs are measured and attributed to electron‐hole pair–phonon coupling and carrier–carrier scattering.