Synthesis of Light-Emitting Carbon Dots and Nanorods: Shape Control and Emission Mechanism

Abstract

Carbon dots (CDs) – small crystalline or amorphous carbon-based nanoparticles – have attracted much attention as promising fluorescent materials for a wide range of applications. A widely accepted advantages of CDs is the simplicity of the formation of highly luminescent CDs from a wide variety of organic precursors. The main contribution of this thesis is summarized as follows.

In the introduction part, we analyze recent related studies identifying the presence of organic fluorophores in CDs with an emphasis on the optical properties of the synthesis products, showing that their emission characteristics may be a complex interplay of stand-alone molecular fluorophores and their aggregates, possibly embedded in an amorphous carbon/polymer network.

First, in order to understand the factors that influence the emission of CDs, we compare three CD species produced by different synthetic approaches, which include: (i) enforcing the carbonization by using graphene oxide as a precursor material; (ii) favoring the formation of molecular fluorophores by conducting the chemical reaction of precursors at lower temperature and ambient pressure, and (iii) applying two different nitrogen precursors, namely ethylenediamine and triethanolamine. After discussing the structural and optical properties of the resulting materials, we focus on the relationship between CDs and molecular fluorophores. By studying the stability of the samples under UV irradiation, we show that molecular fluorophores experience protection from photobleaching, which points towards their incorporation into the carbonized matrix.

Second, we developed a novel solvothermal synthetic stratagem for the synthesis of one-dimensional carbon nanorods (CNRs) with nanometer size, which was achieved by using inverse micelles based on growth of Polyhedral Oligomeric Silsesquioxane (POSS). The produced CNRs exhibit dual color (blue and yellow) emission with a linear polarization, with emission anisotropy of up to 0.3.

Third, we demonstrated a possibility to realize multicolor emission patterns from the composite material which combines light-emitting red or green-emitting CdTe QDs with blue-emitting CDs encapsulated in a cellulose paper treated with polyurethane. The use of these light-emitting nanomaterials makes it possible to realize red/green/blue (RGB) pixelated patterns, while the polyurethane component offers a self-healing function, making it possible to section individual color sheets and rearrange the fragments as basic RGB pixel elements in a building brick-like fashion.

The last chapter of this thesis provides the summary and some perspectives for the future developments of the field of light emitting carbon nanomaterials.

Date of Award	14 Jun 2019
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Andrey ROGACH (Supervisor)