Nanoscience and Microsystems ETDs

Publication Date

Spring 4-12-2018

Abstract

Semiconducting nanocrystals, also known as quantum dots (QDs), that emit light with near-unity quantum yield and are extremely photostable are attractive options as down-conversion and direct electricity-to-light materials for a variety of applications including solid-state lighting, display technologies, bio-imaging and optical tracking. Standard QDs with a core/thin shell structure display fluorescence intermittency (blinking) and photobleaching when exposed to prolonged room temperature excitation for single dot measurements, as well as significant reabsorption and energy transfer when densely packed into polymers or at high solution concentrations.

We have developed thick shell “giant” QDs (gQDs), ultra-stable photon sources both at the ensemble and single-QD level, i.e., yielding 100% blinking suppression and no photobleaching when exposed at room-temperature to high-power laser excitation for extended periods (at least 1 hour) as “bare” solid-state nanocrystals. gQDs further exhibit significantly suppressed non-radiative Auger recombination and minimal self-reabsorption, where the latter is due to a large effective Stokes shift between absorption (primarily in the shell) and emission (from the core). Previously we developed, red emitting CdSe/CdS core/thick shell (15-20 monolayers) gQDs. These materials are nearly ideal red downconverters for solid state lighting applications (which primarily use blue light emitting diodes (LEDs) and a phosphor to generate white light). Presented herein are the results we obtained when gQDs were densely packed into polymer blocks and placed directly on an LED chip and tested for stability and downconversion efficiency. Additionally, for potential utilization of any nanoparticles in commercial applications that demand large volumes of consistent materials, fast methods for materials discovery and optimization are needed. Thus, the ability to scale-up benchtop chemistry is also critical, as is maintaining batch-to-batch and within-batch consistency. To undertake this challenge in our laboratory, we developed a customized fully automated batch reactor system (FABRS) that allows for high throughput synthesis and material scale up. Within are some of the first results we have obtained from our FABRS system for a multidimensional synthetic phase space analysis, where automation affords rapid correlation between synthetic parameters and gQD material properties. We are also interested in the development of new materials, and so a novel gQD material will be discussed, IR emitting PbSe/CdSe/CdSe gQDs. These gQDs allow, for the first time with any lead chalcogenide IR emissive QD, observation at a single dot level using standard detection methods.

Keywords

Nanoscience, Chemistry, Quantum Dots, Synthesis, Materials Development

Sponsors

Department of Energy, Los Alamos National Laboratory LDRD

Document Type

Dissertation

Language

English

Degree Name

Nanoscience and Microsystems

Level of Degree

Doctoral

Department Name

Nanoscience and Microsystems

First Committee Member (Chair)

John K. Grey

Second Committee Member

Diane S. Lidke

Third Committee Member

Andrew P. Shreve

Fourth Committee Member

Jennifer A. Hollingsworth

Fifth Committee Member

Han Htoon

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