Ultrafast localized exciton dynamics in ${\mathrm{Zn}}_x{\mathrm{Cd}}_{1-x}\mathrm{Se}-\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ multiple quantum wells

Localized exciton dynamics and its influence on the ultrafast nonlinear excitonic response are investigated in ${\mathrm{Zn}}_x{\mathrm{Cd}}_{1-x}\mathrm{Se}-\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ multiple quantum wells by means of a two-color femtosecond absorption-saturation technique. A delayed rise of the induced transmission around the heavy- and light-hole exciton lines is observed when localized excitons are photoexcited, yielding evidence for exciton detrapping on a few picosecond time scale. Pump photon energy-dependent measurements show that the photoinjected cold excitons migrate toward higher-energy states at a rate of about $11\hspace{0.5em}\mathrm{m}\mathrm{e}\mathrm{V}/\mathrm{p}\mathrm{s}.$