Preparation and luminescent properties of ZnO quantum dots nanocomposites

Nanocomposites consisting of quantum dots (QDs) incorporated within polymer matrices have attracted great research interests due to their unique functional properties combining the advantages of both inorganic semiconductors and organic polymers. Among various inorganic-organic nanocomposites being studied, ZnO QDs incorporated within different polymer matrices have been widely studied and the nanocomposites exhibit good luminescent properties with high photostability. Nevertheless, there is still lack of study concerning the electroluminescent properties of ZnO QDs nanocomposites. The objectives of this work are to explore a facile method to synthesize polymer/ZnO QDs nanocomposites thin films and to further investigate their luminescent properties. Nanocomposites synthesized via in-situ thermal decomposition of zinc precursor at relatively low temperature, termed as ‘polymerothermal method’, are free of impurity and therefore very suitable for fundamental studies on luminescent properties. Furthermore, the large interface area between polymers and ZnO QDs is very important to study the defect related emission from ZnO QDs and the possible interaction between them. In this work, poly(methyl methacrylate) (PMMA)with good optical transparency was firstly employed for preparation of nanocomposite with uniformly embedded ZnO QDs. The as-prepared PMMA/ZnO QDs nanocomposite exhibits photoluminescence (PL) with strong UV emission but weak visible emission, which is similar to those nanocomposites that synthesized via physical blending method. However, it is interesting to find that the electroluminescence (EL) of PMMA/ZnO QDs nanocomposite based light-emitting devices (LEDs) shows broad emission covering the entire visible range. Based on a detailed analysis carried out by comparing both the PL and EL emission spectra; different carrier recombination pathways corresponding to band edge and defect energy levels are proposed. This finding indicates that the luminescent properties of the nanocomposite are largely depended on the carrier injection method as well as the intrinsic properties of embedded ZnO QDs. The synthetic method was further extended to other polymers. The luminescent properties of nanocomposites can obviously be affected by the polymer matrices; as the polymers can passivate the surface of embedded ZnO QDs to different extents. EL of as-fabricated ZnO QDs based LEDs can be potentially tuned by selection of polymer matrices. The results indicate that the interaction involved between polymers and ZnO QDs could be the key factor of changing the properties of hybrid nanocomposites system.DOCTOR OF PHILOSOPHY (MSE