Wavelength-dependent hot electron relaxation in PVP capped CdS/HgS/CdS quantum dot quantum well nanocrystals

Subpicosecond pump-probe transient absorption spectroscopy has been used to examine the probe wavelength-dependent kinetics of PVP capped CdS/HgS/CdS quantum dot quantum well nanoparticles. Using 398- and 520-nm excitations, the relaxation of the excited hot electrons above the band gap state is characterized by both rapid electronic nonradiative relaxation and slower thermal relaxation processes. The wavelength dependence of both the fast rise and fast decay of the transient bleach is discussed in terms of electronic relaxation processes involving mixed CdS/HgS states at short probe wavelengths or pure HgS states at long probe wavelengths. The slow decay of the transient bleach is discussed in terms of a thermal relaxation process leading to the dissipation of heat from the hot nanoparticle lattice to the surrounding medium.