| The chapters in this thesis address the challenges in doping various semiconductor nanocrystals. By introducing transition metal dopants into naocrystalline semiconductors, the diluted magnetic semiconductors (DMSs) Ni2+-doped SnO2, Co2+- and Mn2+-doped CdSe, Co2+-doped CdS, and CdSe/Co2+:CdS core/shell quantum dots were prepared. In Ni2+:SnO2, the dopant environments were carefully characterized and it was determined that the Ni2+ resides in substitutional Sn4+ lattice sites. It was determined that gentle heating of the Ni2+:SnO 2 nanocrystals resulted in activation and deactivation of ferromagnetism, which was attributed to the generation and passivation of grain-boundary defects. In a separate study, a literature preparation designed to synthesize Co 2+-doped CdSe quantum dots was shown to unexpectedly yield CdSe/CdS core/shell nanocrystals, with the Co2+ dopants segregated into the CdS shells. The synthesis was subsequently modified to exclude all sulfide sources, and Co2+- and Mn2+-doped CdSe quantum dots were successfully characterized using various spectroscopies. Using magnetic circular dichroism (MCD) spectroscopy, sp-d exchange in these colloidal quantum dots was demonstrated for the first time. Post-processing of Mn2+-doped CdSe quantum dots in a blend of surfactants resulted in a substantial increase in the photoluminescence quantum yields, and magnetic circularly polarized luminescence (MCPL) spectra were collected for the first time on any doped colloidal quantum dot. The demonstration of sp-d exchange by two independent measurements provides an excellent description of the dopant-carrier exchange interactions and offers the opportunity to explore new device architectures and experiments in doped CdSe quantum dots. |
