Intra-band Exciton Dynamics of Quantum dot

Quantum dots absorbing mid-infrared light have been synthesized and electron dynamics induced by infrared field is examined with IR pump-probe (IRPP) spectroscopy. We observed the ultrafast electron relaxation dynamics of dodecanethiol-doped HgS CQDs. IR pump-probe experiments reported pump power-independent ultrafast decaying dynamics (1.2 ± 0.1 ps) accelerated by Auger process in CQDs with biexciton generation and slow decay process (>300 ps) caused by Phonon bottleneck for CQDs with single photon absorption. However, the origin of the observed intermediate component (20~60 ps) remains unclear although the inter-sublevel transition between the split states due to spin-orbit coupling was suggested. To further study these intermediate dynamics and the size-dependence of intra-band Auger process, we prepared HgSe CQDs with three different size and investigated intraband exciton dynamics with IR pump-probe spectroscopy. Surprisingly, we found that the oscillation signal, appearing around 10 ps, becomes more pronounced with the increase in CQD size. Furthermore, the observed oscillation signal shows the contribution of photo-induced absorption and excludes the previous assignment of oscillation with the increased bleaching signal from the refilling electrons after Auger process. To reveal the origin of oscillation signal, we employed two-color IRPP (2CIRPP) to track the electron dynamics within the whole intraband.