Deirdre M. O'Carroll

Microcavity effects and optically pumped lasing in single conjugated polymer nanowires

Conjugated polymers have chemically tuneable opto-electronic properties and are easily processed, making them attractive materials for photonics applications. Conjugated polymer lasers, in a variety of resonator geometries such as microcavity, micro-ring, distributed feedback and photonic bandgap structures, have been fabricated using a range of coating and imprinting techniques. Currently, one-dimensional nanowires are emerging as promising candidates for integrated, subwavelength active and passive photonic devices. We report the first observation of optically pumped lasing in single conjugated polymer nanowires. The waveguide and resonator properties of each wire are characterized in the far optical field at room temperature. The end faces of the nanowire are optically flat and the nanowire acts as a cylindrical optical cavity, exhibiting axial Fabry-Pérot mode structure in the emission spectrum. Above a threshold incident pump energy, the emission spectrum collapses to a single, sharp peak with an instrument-limited line width that is characteristic of single-mode excitonic laser action.

Conjugated Polymer/Metal Nanowire Heterostructure Plasmonic Antennas

The spontaneous emission spectrum, polarization direction, and emission lifetime of monolithically coupled poly-(3-hexylthiophene), P3HT, light-emitting nanostructures are modified by gold nanowire antennas. The P3HT nanostructure is integrated onto the end of the gold nanowire antenna, where localized, longitudinal surface plasmon mode fields are strongest. Comprehensive optical characterization and theoretical modeling are employed to demonstrate plasmonic nanoantenna-mediated light emission from P3HT.

Solution-Processed MoS2/Organolead Trihalide Perovskite Photodetectors

Integration of organic/inorganic hybrid perovskites with metallic or semiconducting phases of 2D MoS2 nanosheets via solution processing is demonstrated. The results show that the collection of charge carriers is strongly dependent on the electronic properties of the 2D MoS2 with metallic MoS2 showing high responsivity and the semiconducting phase exhibiting high on/off ratios.

Absorption-Induced Transparency†

In the past decade, the field of optics has been stimulated by new concepts such as plasmonics and extraordinary optical transmission, which are paving the way for next-generation photonic components. In this context, hybrid materials that combine the properties of structured metals with semiconductor or molecular materials to create novel functionalities offer much potential. While studying molecule– metal interactions, we have found a new phenomenon whereby molecules can induce transparency in optically thick metal films perforated with subwavelength holes. Nonintuitively, transparent windows are opened up at wavelengths at which the molecules absorb strongly, that is, where one would normally expect no transmission. Here we report a detailed study of this phenomenon showing, among other things, that the molecular material must be within the dipole coupling distance (less than ca. 20 nm) from the metal surface, and that the mechanism involves surface plasmons but is independent of the arrangement of the holes. The phenomenon thus provides new flexibility for tailoring extraordinary optical transmission through subwavelength holes and points to new directions for preparing plasmonic hybrid materials for photonics and energy-conversion applications. Absorption-induced transparency (AIT) is best illustrated by the schematic and spectra in Figure 1. Figure 1a shows the transmission spectrum of a square array of 100 nm-diameter holes milled by focused ion beam (FIB) in a 200 nm-thick Ag film with a period of 250 nm (black curve). Only the transmission peak associated with the (1,0) surface plasmon (SP) resonance on the glass/metal interface of the hole array is visible at 518 nm. When an approximately 30 nm layer of a J-aggregate of a cyanine compound (2,2’-dimethyl-8-phenyl5,6,5’,6’-dibenzothiacarbocyanine chloride) is adsorbed on the hole array, its transmission spectrum shows an intense new transmission with a sharp onset at 685 nm (red curve). Figure 1b shows the absorption spectrum of the cyanine Jaggregate layer (measured as 1 reflection) taken on a

Absorption-induced scattering and surface plasmon out-coupling from absorber-coated plasmonic metasurfaces

Interactions between absorbers and plasmonic metasurfaces can give rise to unique optical properties not present for either of the individual materials and can influence the performance of a host of optical sensing and thin-film optoelectronic applications. Here we identify three distinct mode types of absorber-coated plasmonic metasurfaces: localized and propagating surface plasmons and a previously unidentified optical mode type called absorption-induced scattering. The extinction of the latter mode type can be tuned by controlling the morphology of the absorber coating and the spectral overlap of the absorber with the plasmonic modes. Furthermore, we show that surface plasmons are backscattered when the crystallinity of the absorber is low but are absorbed for more crystalline absorber coatings. This work furthers our understanding of light–matter interactions between absorbers and surface plasmons to enable practical optoelectronic applications of metasurfaces.

Conjugated polymer-based photonic nanostructures

Conjugated polymer materials are at the forefront of many next-generation organic optoelectronic technologies including organic light-emitting diodes, photovoltaics and lasers. The photophysical properties of these materials can be controlled and optimized through the formation of nanoscale-confined geometries such as nanoparticles, aggregates, nanofibers, or thin films. In this review, we discuss the photonic characteristics of conjugated polymer-based nanostructured materials and devices with a focus on how excitons and photons can be manipulated and managed though confinement of polymer chains and through interactions with inorganic nanostructures. We include case studies from the literature on how internal molecular morphology can be controlled in conjugated polymer thin-film optoelectronics, nanowires and nanofibers and, in turn, how internal morphology affects the photonic properties of these structures. Extrinsic approaches to controlling or modifying the photonic properties of conjugated polymer materials and devices through the addition of inorganic photonic nanostructures are also discussed.

Metal–Polymer–Metal Split‐Dipole Nanoantennas

The conjugated polymer semiconductor poly(3-hexylthiophene), (P3HT), is integrated directly into the slot region of resonant plasmonic split-dipole nanoantennas. The P3HT radiative emission rate is enhanced by a factor of up to 29, in experiment, and 550 for the ideal case, due to the large local density of optical states in the nanoantenna slot region. Additionally, the theoretical modified luminescence quantum efficiency is shown to increase from 1% to 45% for optimized nanoantenna parameters.

Light-management in ultra-thin polythiophene films using plasmonic monopole nanoantennas

Deposition of vertical, cone-shaped plasmonic nanorod arrays onto sub-50 nm polythiophene films on Ag substrates is shown to result in significant absorption enhancement (>12 at the polythiophene band edge) and spectral broadening (more than 250 nm increase) relative to polythiophene/Ag films without plasmonic nanorod arrays. Full-field electromagnetic simulations are used to identify the modes of the plasmonic nanorod array/polythiophene/Ag film system. Both gap modes and longitudinal monopole antenna modes give rise to highly localized electric fields in the polythiophene film and are the primary contributors to polythiophene absorption enhancement. This approach is suitable for large area optoelectronic applications where light management in ultrathin active layers is desired.

Enhancing surface plasmon leakage at the metal/semiconductor interface: towards increased light outcoupling efficiency in organic optoelectronics

The light outcoupling efficiency of organic light-emitting optoelectronic devices is severely limited by excitation of tightly bound surface plasmon polaritons at the metal electrodes. We present a theoretical study of an organic semiconductor-silver-SiO(2) waveguide and demonstrate that by simple tuning of metal film thickness and the emission regime of the organic semiconductor, a significant fraction of surface plasmon polariton mode amplitude is leaked into the active semiconductor layer, thereby decreasing the amount of optical energy trapped by the metal. At visible wavelengths, mode leakage increases by factors of up to 3.8 and 88 by tuning metal film thickness and by addition of gain, respectively.

The role of photonics in energy

Abstract. In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects.