Semiconductor nanocrystal composite materials and devices

Abstract

This thesis describes the synthesis and characterization of semiconductor nanocrystal (quantum dot, QD) embedded composite materials and possible device applications of the resulting luminescent materials. Chemically synthesized ZnS overcoated CdSe, (CdSe)ZnS, QDs are incorporated into a polymer host material. The main challenge in the preparation of QD-polymer composites is the prevention of both phase separation and aggregation of the QDs within the polymer host material, while sustaining the original quantum efficiency of the QDs in their growth solution. Possible ways to incorporate QDs into an optically clear polymer matrix are considered. A guideline for a successful QD-polymer composite is discussed for various polymer systems: ligand polymers, ligand monomer and covalent bonding to a polymer matrix, and in-situ polymerization. The best composite system is based on incorporation of QDs into a poly(laurylmethacrylate) matrix during in-situ polymerization in the presence of TOP ligands. The successful incorporation of QDs into a polymer host material demonstrates the ability to form QD-polymer composite light emitting materials. The emission spans nearly the entire region of saturated and mixed colors with narrow emission profiles. The light emission spectra of QD-polymer composites excited by a blue diode light are also simulated by Monte Carlo methods and compared to the measured spectra from actual devices. The synthesis and characterization of QD-microspheres, which can be used as active fluorescent building blocks, are also described.

(cont.) In order to enhance the stability and compatibility of QDs in a polymer microsphere, the QDs are treated with polymerizable phosphine ligands, small oligomeric phosphine methacrylate (SOPM), and the following homogeneous solution polymerization is investigated to form monodisperse QD-microspheres. The QD-microspheres can store optical information assigned by embedded QDs in multiple codes. The surface functionalization of these capsules could provide a means for attaching capsules to surfaces and allow capsules to assemble into 3D structures.