| Electronic relaxation phenomena are studied in II-VI colloidal quantum dots. Information regarding confinement is obtained using intraband spectroscopy. Slow intraband relaxation is observed in heterostructures where the coupling of electrons to holes, surfactant vibrations and surface states has been eliminated. This is consistent with the expectation of a phonon bottleneck effect in strongly confined quantum dots. Facile electron extraction is observed from the CdSe P electronic level in quantum dots where exposed ZnSe facets are present. The rate of extraction may be enhanced to the extent that mid-infrared excitation can lead to luminescence quenching. Multicarrier recombination rates are studied in different heterostructures, and it is seen that electron confinement and not electron-hole overlap seems to be responsible for enhancement of non-radiative decay of multiexcitons in quantum dots. This is an unexpected result, inconsistent with the accepted Auger decay picture of multiexcitons. Finally, it is suggested that transition metals may be used as impurity dopants to achieve permanent carrier populations in quantum dots. We demonstrated presence of holes in heterostructures doped with copper, and this motivates further studies concerning the interactions of these carriers with paramagnetic impurities. |
