Photo induced semiconductor quantum rods alignment and its application in modern liquid crystal displays

Abstract

Semiconductor nanocrystals, also termed quantum dots (QDs) or quantum rods (QRs), have been extensively studied due to their excellent optical properties. In addition to spherical QDs, the anisotropic property of QRs results in polarized absorption and emission along the long axis of the nanocrystal. In order to retain these beneficial properties in films, QRs need to be unidirectionally in-plane oriented, which has been attempted by a number of different approaches. In this regard, this thesis explores the method to unidirectionally align QRs by the photo-induced alignment technique, which was originally developed for the alignment of liquid crystals. It is shown that the strategy facilitates the alignment of highly luminescent CdSe/CdS core/shell QRs in the aligned liquid crystal monomer (LCM), obtaining solid QRs in a liquid crystal polymer (LCP) matrix after UV polymerization. Optical and structural characterization reveals QR alignment with highly polarized emission, indicating the high order parameter. To further understand this composite system, many fundamental studies have been carried out. The QR aligning dynamic study shows good agreement of the polarized emission property with the aligning order parameter; the estimated highest polarization ratio of a single QR from fluorescence anisotropy measurement offers a quick evaluation of the polarized emission property from QRs/LCP composite film; the concentration effects of both QRs and the LCM provide information for balancing the internal molecular interactions; the optimization of the surface ligands architectures indicates that the combination of promesogenic dendritic ligands with the short alkylphosphonic acids group shows the best compatibility with the LCM. In application aspects, the microscale (down to 2 μm domain size) pattern alignments of QRs in an LCP matrix show potential in photonic and security areas, the combination of QRs/LCP composite film with liquid crystal technology present new photo-emissive displays, and the QR enhancement film improves both color performance (> 100% NTSC) and optical efficiency (> 8%) for modern liquid crystal display applications.

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology