Interactions of light with nanostructured materials

This thesis explores the use of light-matter coupling to address key challenges in exciton transport in organic semiconductors, tuneable light-emission and UV plasmonic materials. Organic photovoltaics are promising candidates for solar energy capture; however, their performance is limited due short exciton diffusion lengths in organic semiconductors. To address this challenge, the design of biomimetic organic light-harvesting networks capable of strong plasmon-exciton coupling is explored. Pigment-polymer antenna complexes are formed by attachment of chlorophyll a (Chl) to poly(cysteine methacrylate) (PCysMA) scaffolds grown by surface-initiated atom-transfer radical polymerisation from brominated self-assembled monolayers. The organisation of Chl within the films is programmed by controlling the polymer grafting density and polymerisation time. The films are characterised using X-ray photoelectron spectroscopy (XPS) depth-profiling with giant gas cluster ions. For all grafting densities, Chl are distributed uniformly as a function of depth. However, the fraction of repeat units bound to Chl increases with decreasing grafting density. When synthesised from gold nanostructures, the plasmon-exciton coupling energies are correlated with the grafting density of the polymer layer, yielding plasmon-exciton coupling energies as high as 0.46 eV. Thus, it is demonstrated that plexcitonic complexes are promising templates for the design of biomimetic photonic materials with long-range energy transfer mechanisms. In the field of light-emission technologies, metal halide perovskite quantum dots (PQDs) have emerged as promising materials due to their exceptional photoluminescence (PL) properties. A wide range of applications could benefit from adjustable luminescence post-synthesis. In this work, an optical nanoantenna array is designed with polarization-controlled quasi-bound-states-in-the-continuum (q-BIC) resonances that can control and modify the perovskite PL wavelength. Si nanopillar arrays are fabricated using electron-beam lithography (EBL) that exhibit q-BIC resonances in the range of 690 nm to 804 nm under y-polarization, and from 638 nm to 696 nm under x-polarization. The energies of these resonances are tuned by variation of the nanostructure geometries. FAPbI3 perovskites are deposited on the arrays using dip-coating and the optical properties are characterised using PL mapping measurements. A wavelength shift over a ~39 nm range was achieved, with additional spectral tuning enabled by the switching of the pump laser polarization. The design confers a 21-fold emission enhancement of the QDs. The research provides a path towards spectrally tailored quantum emitters. Lastly, interband plasmons (IBPs) are of interest as they enable plasmonic behaviour in non-plasmonic materials, such as semiconductors. IBPs arise from the electromagnetic excitation of bound electron oscillations, enabling plasmonic resonances into the deep ultraviolet (UV) range. Despite their significant potential, practical applications are limited due to their broad resonances. This thesis demonstrates the sharpening of the resonances of IBPs by more than one-order of magnitude via mode hybridization. Si nanodisk arrays are fabricated using EBL on top of a SiO2 cavity. The optical response of the system is controlled by the geometrical design, which influences the interaction between the Si nanodisk plasmon resonances and the cavity modes. The experimental and simulated reflectance show a Q-factor enhancement from 1 to ~43. This high-Q resonance further increases light absorption of UV absorbing lignin-modified polyethylene glycol films by 7.5-fold. Our findings could be applicable to other interband plasmonic materials and open up possibilities in applications requiring both narrow and broad band resonances, particularly in UV specific areas.