Excitonic recombination and relaxation in CdS quantum dots

Size-selective spectroscopic techniques and a tight-binding calculation wit h restricted configuration interaction are used to study the recombination and the relaxation of excitons in CdS quantum dots. The optical absorption spectrum is calculated and is found to be close to the experiments. The ana lysis of the luminescence shows that an emission of light corresponding to transitions between quantum confined states is obtained only in QDs larger than 3 nm. The exciton levels are compared with those given by simple effec tive mass approximation. The photoluminescence excitation spectra suggest t hat for upper exciton levels non-radiative captures of the carrier may beco me competitive compared to relaxation processes.