UV Nano-Lights: Nonlinear Quantum Dot-Plasmon Coupling
Abstract
This research involved using a new approach to measure nonlinear absorption using the single beam Z-scan technique. By measuring the delay or advance of a light pulse reaching the detector, the nonlinear absorption could be identified as either instantaneous or transient. It was demonstrated that with this modification of the Z-scan technique, discrimination of excited state absorption (ESA) from two and three photon nonlinear absorption could be achieved. A colloidal suspension of ZnO nanocones in ethanol was the model system used to test the efficacy of this technique, where it was shown that when irradiated by high fluence 532 nm nanosecond pulses, nonlinear absorption that was 5 orders of magnitude larger than in bulk media occurred, mostly due to ESA not two photon absorption. Importantly this showed that by control of size and shape that the nonlinear optical properties of ZnO can be dramatically increased and that a new measurement technique was developed that can separate multi-photon nonlinear absorption processes. Another important outcome of the work was development of a method to accurately measure the thickness of a thin organic molecule layer coating on small inorganic quantum dot particle cores using dynamic light scattering (DLS). The investigators demonstrated that a simple correction formula accurately yields hydrodynamic size in both the volume- and number-weighted size distributions, from which a precise determination of molecular shell thickness by DLS can be obtained. Small (core size < 5 nm) nanoparticles of ZnO and Au, coated with a layer of dodecanethiol were used for demonstration. The method can be widely applied to many systems. It can be used to find the capping thickness of different ligand coatings, or if capping thickness is known, this technique can be used to find particle size distributions using DLS alone. The method is also applicable to bare nanoparticles in polar solvents.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2014
- Accession Number
- ADA606642
Entities
People
- Eric Waclawik
Organizations
- Queensland University of Technology