Author ORCID Identifier

https://orcid.org/0000-0001-9394-5385

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Chemistry

First Advisor

Dr. Doo Young Kim

Abstract

Photoluminescent­ (PL) nanomaterials play an important role in areas including displays, sensing, solar, photocatalysis, and bio applications. Traditional methods to prepare PL materials suffer many drawbacks such as harsh chemical precursors, complicated synthetic steps, and production of many byproducts. Laser ablation in liquid (LAL) has emerged as a promising alternative to prepare materials that is single-step, fast, uses fewer precursors, produces fewer side products, and has simple purification steps. During LAL, a solid target is irradiated with a pulsed laser source. The laser pulses cause plasma plumes of the target material to form which are cooled, condensed, and can react with the surrounding liquid. This dissertation explores LAL as an alternative method to produce two important classes of PL nanomaterials: graphene quantum dots (GQDs) and upconverting nanoparticles (UCNPs). GQDs are a class of carbon PL materials that are lightweight, biocompatible and can be produced from cheap and abundant carbon sources. Their PL properties depend on both radiative recombination of intrinsic states through their carbon backbone as well as defect like states from surface functionalization. LAL of carbon nano-onions in water was used to produce GQDs. These GQDs were systematically compared to those produced by a traditional chemical oxidation method and showed blue shifted emission, higher fractions of hydroxyl-groups, and smaller sizes. Nitrogen doping with controlled chemical composition allowed further tuning of the PL and was achieved by including dopant molecules in the liquid during LAL. Lifetime measurements showed three emissive pathways and provided greater understanding of the roles of intrinsic and defect like emissive states. UCNPs composed of NaYF4:Yb3+/Er3+ are interesting for many bio applications but are challenging to prepare with both high upconversion efficiency and water solubility. Control of the UCNP phase is important for high efficiency. LAL was used to address these issues by irradiating a target of desired phase in an aqueous solution containing capping agents which allowed for formation of water soluble UCNPs of the desired phase. Tuning of laser parameters allowed control of the size, composition, and PL of the UCNPs. This work showcases LAL as a method to efficiently produce PL nanomaterials with controlled properties.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.218

Funding Information

University of Kentucky Research Challenge Trust (2016-2019)

Kentucky Science and Engineering Foundation (KSEF-3884-RDE-020, 2015-2018)

National Science Foundation under Cooperative Agreement (No. 1355438, 2015-2020)

National Science Foundation Division of Chemistry (No. 1800316, 2018-2020)

Available for download on Friday, November 20, 2020

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