Quantum Optoelectronics

Abstract:

The photocatalytic overall water splitting (POWS) reaction using particulate catalysts is considered as an ideal approach for capturing solar energy and storing it in the form of hydrogen, however, current POWS systems are hindered by the slow separation but fast recombination of the photo-generated charge carriers, hence giving unsatisfactory performances. Here we report a dramatically improved POWS system for a Au-supported Fe₃O₄/N-TiO₂ superparamagnetic photocatalyst promoted by local magnetic field effects. Strong local magnetic flux was induced by a weak external magnetic field of 180 mT, which then resulted in a quantum efficiency of 88.7% at 437 nm at 270 °C without any sacrificial reagent. The mechanism of the magnetic field effects was explored systematically and quantitatively by time-resolved spectroscopic technique and first-principles calculations, which suggested such enhancement was due to the greatly prolonged excitonic lifetime, originating from both the Lorentz force and spin-polarisation effects. By controllable manipulation of both features using local magnetic field, an unprecedented solar-to-hydrogen conversion efficiency of 11.9 ± 0.5% and an overall energy efficiency of 1.16 ± 0.05% were achieved in a particulate POWS system under AM 1.5G simulated solar illumination, which exceeds the STH goal of 10% for practical applications of POWS systems imposed by the United States Department of Energy.

Abstract:

We report on the experimental observation of mirror-enhanced directional surface-enhanced Raman scattering (SERS) from a self-assembled monolayer of molecules coupled to a nanowire-nanoparticle (NW-NP) junction on a mirror in a remote excitation configuration. Placing the NW-NP junction on a metallic mirror generates multiple gap plasmon modes that have unique momentum space-scattering signatures. We perform Fourier plane imaging of the SERS from the NW-NP on a mirror to understand the effect of multiple hotspots on molecular emission. We systematically study the effect of the ground plane on the directionality of emission from the NW-NP junction and show that the presence of a mirror drastically reduces the angular spread of emission. The effect of multiple hotspots in the geometry on the directionality of the molecular emission is studied using 3D numerical simulations. The results presented here will have implications in understanding plasmon hybridization in the momentum space and its effects on molecular emission.

Abstract:

We have designed a method of harvesting electrical energy using plasmon-enhanced light pressure. A device was fabricated as a cut cone structure that optimizes light collection so that the weak incident light pressure can be sufficiently enhanced inside the cut cone to generate electrical energy. An increase in the device's current output is a strong indication that the pressure of incident light has been enhanced by the surface plasmons on a platinum layer inside the cut cone. The electrical energy harvested in a few minutes by irradiating pulsed laser light on a single micro device was possible to illuminate a blue LED.

Abstract:

Abstract:

Covalent triazine frameworks (CTFs) synthesized through nucleophilic substitution of 4,4’ bipyridine on the carbon atoms of cyanuric chloride were studied as fluorescent sensors. The band gap of the materials was calculated to be 2.95 eV from diffuse reflectance measurements, while from the adsorption in aqueous dispersions, we obtained the value of 3.7 eV. A partial exfoliation of the layered CTFs in water or tetrahydrofuran led to different morphologies, increased emission lifetime and fluorescence quantum yield. The pattern of their light emission properties in combination with their redox states was defined with the addition of a series of acidic and basic analytes. Another unique aspect of these semiconducting materials is the induced aggregation and the subsequent enhancement of emission under ultraviolet illumination.