| dc.description.abstract | For this work we are interested in two heavy-metal free semiconductor nanomaterials that could be incorporated as the fluorophores in luminescent solar concentrators and LEDs; copper indium sulphide (CuInS2) and indium phosphide (InP). For InP NCs we are interested in a relatively new synthesis method of InP quantum well nanocrystals (NCs). For these structures the InP NCs are comprised in the shell, in this way the PL can potentially cover the entire visible spectrum and into the near-infrared (NIR) by controlling the shell thickness. The synthesis method proved to be very complicated and no proof of a successful synthesis was obtained. Characteristic for CIS NCs is a broad photoluminescence (PL) bandwidth, this is disadvantageous for its potential application in LSCs. A thorough understanding of the nature of this broad band could provide insights on ways to narrow the PL band. Different line broadening effects are studied using various ensemble techniques and single particle spectroscopy. The results of these experiments indicate that the broad PL bandwidth observed for CIS NCs partly arises due to inhomogeneities in the sample. Single particle spectroscopy substantiates this claim, by showing strongly decreased PL bandwidths at the single particle level. Nevertheless, this reduced bandwidth is still considerably broader than observed for their cadmium-containing analogues. As such part of the broad PL band is intrinsic to the material as well. To study the fundamental principles behind this broad intrinsic PL bandwidth, the exciton recombination pathways in CIS NCs is studied using power dependent transient absorption spectroscopy. With the results of these experiments we reproduce the experimental proof for the two-fold degeneracy of the quantized electron in the CB, identifying the hole as the localized carrier in the exciton recombination process. In addition, the TA data shows a blueshift of the bleach signal upon increasing the pump power. We attribute this shift to fast non-radiative Auger recombination of e-h pairs with a good wavefunction overlap in the multi-exciton regime, leaving the energetically higher excitons thus shifting the bleach signal to the blue. To validate this idea the experiment described in this work have to be repeated using different CIS NCs samples in order to exclude the contribution of the large size distribution to the observed blueshift. | |
