Control under Optical, Nonlinear Optical and Kinetic Properties of Two-Dimensional Gradient Cdse1-Xsx Nanocrystals

Peculiarities of photoluminescence (PL) and absorption spectra of gradient nanocrystals CdSe1-xSx colloidal solution were studied by pump and probe technique under stationary excitation of excitons by nanosecond laser pulses. The PL peaks and differential transmission peaks positions changing were revealed with the CdSe1-xSx nanocrystals composition variation. Bleaching of excitons transitions was observed for high pump intensities and explained by excitons space filling effect. The changing of the differential transmission peaks positions was explained by the nanocrystal band gap dependence on the chemical composition. Time-resolved PL measurements from the sub-picoseconds to tens of nanoseconds range demonstrated a strongly different behavior for gradient nanocrystals and pure CdSe nanocrystals. For pure nanocrystals two typical time-scales were resolved contrary to the gradient nanocrystals where (with the growth of sulfur concentration) only a single time scale was revealed. The observed modification of time-resolved PL for gradient nanocrystals is caused by the presence of traps in the gradient samples due to the chemical composition modification.