Date of Award
Doctor of Philosophy (PhD)
Physical Sciences and Mathematics
Understanding the fundamental principles behind transition metal ion doped semiconducting materials has drawn immense interest when designing ideal systems for use in optical and electronic devices. Dopant ions have been found to diffuse/migrate throughout solid materials when the thermal energy of the system is elevated above a temperature boundary allowing the cations and anions within a system to move freely. Nanomaterials such as 0-dimensional (0D) quantum dots (QDs), 1D nanorods/nanowires, and 2D nanoplatelets have unique dopant-location dependent optical and electronic properties which can be drastically altered based on the final dopant sites and distribution throughout the material. This work focuses on the mechanism of dopant ion migration behaviors within II-VI nanomaterials during post-synthetic treatments including shelling, high temperature annealing, etc. Specifically, Mn doped CdS QDs and ZnSe nanowires were passivated with ZnX (X = S or Se) shell coatings, at elevated temperatures, were used as model systems to study dopant behaviors. This work demonstrates the formation of a cation alloyed interface between the core and shell lattice forming an intermediate lattice which provides a thermodynamically favorable sites for the dopant ions causing an outward dopant migration. The dopant migration causes a decreased energy transfer between the host-lattice excitons and the dopant ions causing tunable fluorescent spectra. When temperatures were elevated above a temperature boundary (Tb) where the host and shell cations are able to exchange forming a globally alloyed QDs without a distinct core/shell interface, the dopant ions can continue migrating and ultimately ejecting from the QDs. Once the Tb is surpassed, global alloying allows the host excitons to delocalize further throughout the QD, increasing the host-to-dopant energy transfer allowing for a versatile fluorescence.
Hofman, Elan, "Elucidating Dopant Migration Mechanism for the Controlled Dopant Locations/Distribution within Core/Shell Nanocrystals" (2020). Dissertations - ALL. 1219.