Photodoping of Colloidal Nanocrystals

Abstract

This dissertation addresses various aspects of photodoping colloidal nanocrystals. Photodoped ZnO nanocrystals were found to be versatile tuneable reducers using both quantum confinement and band-gap engineering with Mg2+ doping to change the conduction band potential. Using photoluminescence of the visible trap and magnetic circular dichroism spectroscopy of Mg2+ and Mn2+ co-doped ZnO, Mg2+ was shown to change the potential of both the conduction and valence band in a ratio of 0.68:0.32. The hole scavenging reaction using ethanol as the hole scavenger was investigated using continuous-wave and time resolved photoluminescence of the visible trap state of ZnO. The reaction was found to occur between the valence band hole and with a rate of > 15 ps-1. Quenching of the ZnO visible trap luminescence upon photodoping was shown to be due to trap/electron Auger process while the concomitant enhancement of the UV band-gap emission was hypothesized to be due to a reduction in non-radiative processes due to extra electrons in the conduction-band. The trap/electron Auger process in ZnO nanocrystals was further characterized by a size-dependence and shown to scale with R2. Another previously unknown Auger size dependence was measured in CdSe/ZnS trions and shown to scale with R4.3.