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Understanding Photoluminescence Quantum Yield In Cesium Lead Tribromide Nanocrystals
Get PDFSemiconducting nanoparticles have played a pivotal role in advancing optoelectronic technologies. The photoluminescence quantum yield (PLQY), which measures emitted photons relative to absorbed photons, stands as a critical performance metric for these materials, directly influencing device performance. In the case of CsPbX3 (X = Cl^-1, Br^-1 , I^-1 ) nanocrystals (NCs), the electronic structure is determined through the interactions of molecular orbitals within the PbX6^-1 repeating unit. The most prevalent crystal defect in these materials is halide vacancies, which can locally confine excited carriers, resulting in carrier relaxation through non-radiative recombination mechanisms.
This dissertation focuses on understanding the formation of electronic traps within CsPbBr3 NCs and designing effective strategies to mitigate their impact and occurrence. Chapter 2 introduces two precise PLQY measurement methods for colloidal solutions: one compares emission spectra to a reference standard, and the other outlines a custom integrating sphere setup. This chapter provides comprehensive guidance for accurate PLQY measurement, with a particular focus on CsPbBr3 NCs, given that their absorption and emission properties influence PLQY measurement design.
Chapter 3 delves into the design of saturated ligand solutions (SLSs), which I propose as a better solvent system for CsPbBr3 NCs. This endeavor involves a series of iterations with the SLSs formulation to identify specific ligand species conducive to optimal surface trap passivation. Our unique approach to the SLS preparation process enables the introduction of substantial quantities of ligands, previously unachievable through direct ligand addition. Concurrently, the SLSs facilitate continuous dilution of the colloidal solution without compromising the structural and optoelectronic quality of the NCs, addressing a significant field limitation. These methods present novel opportunities to gain insights into ligand interactions within perovskite systems and offer tailored solutions designed for perovskite materials.
Lastly, Chapter 4 demonstrates the potential to limit the impact of electronic trap states in CsPbBr3 NCs when they are incorporated into solution-phase superlattices. Superlattices enable enhanced interparticle electronic coupling interactions due to the close proximity of individual NCs. This results in a more delocalized electronic structure and improved radiative recombination efficiency, offering insights into strategies for enhancing radiative recombination and outcompeting the kinetics of non-radiative electronic processes
Analysis of Acute and Chronic Timepoints of Transplanted Neural Progenitor Cells in a Model of Spinal Cord Injury
Get PDFSpinal cord injury (SCI) affects millions of people worldwide. It results in devastating consequences, including loss of strength, sensation, and motor function at and below the injury site. Currently, there are no treatment options that can even partially restore function to individuals living with SCI. Neural progenitor cell (NPC) transplantation is a promising treatment for promoting the recovery of motor function due to its ability to provide new neurons to sites of SCI that support the formation of new synaptic connections. This is enabled by injured host axons regenerating into NPC grafts, as well as graft-derived axons forming new synaptic connections with spared host systems. However, little is known about how NPC grafts evolve from the weeks to months after transplantation. This is an important question, as stem cell treatments would need to last years if not decades within a patient. To address these questions, I will evaluate the differences in anatomical properties between acute and chronic neural progenitor cell grafts. In this experiment, I will focus on the survival and axon extension of NPC grafts at an acute (6-week) and chronic (24-week) time point. We will evaluate graft survival, cellular composition, graft-derived axon extension, and host axon regeneration into grafts at early and late time points. The impact of this study will show the effectiveness of NPC graft survival in an unknown chronic injury environment and prove NPC transplantation can be used as a long-term treatment for spinal cord injury
