Determination of dopant ion mobility in transition metal doped semiconductor nanocrystals.

摘要

Transition metal doped semiconductor nanocrystals have shown great promise in replacing traditional colloidal semiconductor nanocrystals (q-dots) due to their superior physical properties. Doped colloidal semiconductor nanocrystals, or d-dots, exhibit all of the properties of traditional q-dots but do not suffer from self quenching and thermal degradation. The optical properties of d-dots have been shown to be heavily dependent on the dopant ion location within the nanocrystal. The spatial location of the dopant ions has been shown to change upon heating of the material due to lattice diffusion (movement of the dopant ions within the crystal lattice) and self-purification (ejection of the dopant ion impurities from the crystal lattice) processes. These process were monitored through the use of a newly developed in-situ photoluminescence (PL) spectrometer capable of recording the emission of the sample at high temperatures and over extended periods of time.;Annealing experiments were conducted in which the d-dot sample was heated to elevated temperatures in an effort to measure the diffusion and purification processes. The use of PL enabled a non-intrusive route to monitor the changes in dopant ion location. The results of these annealing studies show that the diffusion of dopant ions occurs at lower temperatures than expected and at a much slower rate than other reports.;The spatial location and distribution of dopant ions was further investigated with a selective oxidative etching method. The method involved the systematic etching of the d-dots, removing material from the surface of the nanocrystals. The elemental composition of each layer was analyzed to determine the composition of material removed. D-dots made with two different synthetic techniques, thus different physical properties, were etched to construct a structural model depicting the dopant ion location from each technique. The two models constructed depict the significant differences in dopant ion location explaining the differences in their respectable optical properties. The oxidative etching method developed can be extended to confirm the structures of other nanocrystalline materials such as core/shell structures. The information obtained from these studies will help to tailor future doped materials to fit practical applications.