Photo Induced Semiconductor Quantum Rods Alignment and its Application in Modern Liquid Crystal Displays
Room 5510 (Lifts 25-26), 5/F Academic Building, HKUST

Thesis Examination Committee

Prof Chi Keung TANG, CSE/HKUST (Chairperson)
Prof Hoi Sing KWOK, ECE/HKUST (Thesis Supervisor)
Prof Vladimir CHIGRINOV, ECE/HKUST (Thesis Co-supervisor)
Prof Sin-Doo LEE, School of Electronic Engineering, Seoul National University (External Examiner)
Prof Zhiyong FAN, ECE/HKUST
Prof Jiannong WANG, PHYS/HKUST



Semiconductor nanocrystals, also termed quantum dots (QDs), 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 unidirectional 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 has originally been 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 liquid crystal polymer (LCP) matrix after UV polymerization. Optical and structural characterization reveals QRs alignment with highly polarized emission, indicating the high order parameter. 

To further understand this composite system, many fundamental studies are carried. The QRs aligning dynamic study shows good agreement of polarized emission property with aligning order parameter; the estimated highest polarization ratio of single QR from fluorescence anisotropy measurement offers the quick evaluation for polarized emission property from QRs/LCP composite film; the concentration effects of both QRs and LCM provide information for balancing the internal molecular interactions; the optimization of surface ligands architectures indicates that the combination of promesogenic dendritic ligands with short alkylphosphonic acids group showing best compatibility with LCM.

In application aspects, the microscale (down to 2 μm domain size) pattern alignments of QRs in LCP matrix show potential in photonic and security areas; the combination of QRs/LCP composite film with liquid crystal technology present the new photo-emissive displays; the QR enhancement film improves both color performance (> 100% NTSC) and optical efficiency (> 8%) for modern liquid crystal display applications.

Room 5510 (Lifts 25-26), 5/F Academic Building, HKUST