Coherent interaction of three-dimensionally confined electron–hole pairs with LO-phonons

The spectrally resolved FWM signal of CdSe quantum dots with sizes below the bulk excitonic Bohr radius has been studied as a function of temperature and excitation intensity and compared with bulk CdSe. A clear oscillation with a period of 163 fs (≈ 25 meV) is found in the transient FWM signal and attributed to a coherent coupling of confined electron–hole pairs with LO-phonons. Two side bands are observed in the spectrum 25 meV below and above the excitonic resonance. The strong coupling to LO-phonons is observed even at excitation densities around 1×1016 cm—3 which is close to the bulk value of the Mott density