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Register a new userPhoton Upconversion with Hot Carriers in Plasmonic Systems
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We propose a novel scheme of photon upconversion based on harnessing the energy of plasmonic hot carriers. Low-energy photons excite hot electrons and hot holes in a plasmonic nanoparticle, which are then injected into an adjacent semiconductor quantum well where they radiatively recombine to emit a photon of higher energy. We theoretically study the proposed upconversion scheme using Fermi-liquid theory and determine the upconversion quantum efficiency to be as high as 25% in 5 nm silver nanocubes. This upconversion scheme is linear in its operation, does not require coherent illumination, offers spectral tunability, and is more efficient than conventional upconverters.
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The phenomenon of upconversion, in which a system sequentially absorbs two or more photons and emits a photon of a higher frequency, has been used in numerous applications. These include high-resolution non-destructive bioimaging, deep-penetrating photodynamic therapy, and photovoltaic devices. Due to the multi-photon mechanism of upconversion, its quantum yield cannot exceed 50%. We propose a new mechanism of upconversion, which is based on single-photon absorption; in this process, unlike in multiple-photon upconversion, the quantum yield can be higher than 50%. We show that in a system of two atoms interacting with a reservoir, a low-frequency excitation of one atom can be upconverted into a high-frequency excitation of another atom. The energy required for such an upconversion is drawn from the reservoir, which destroys coherence. Decoherence leads to the transition of the system from the pure state with a small energy dispersion to the mixed state with greater dispersion of energy, while the system entropy increases. The phenomenon of single-photon upconversion can be used to increase the efficacy of devices utilizing upconversion.
Plasmonic hot carrier devices extract excited carriers from metal nanostructures before equilibration, and have the potential to surpass semiconductor light absorbers. However their efficiencies have so far remained well below theoretical limits, which necessitates quantitative prediction of carrier transport and energy loss in plasmonic structures to identify and overcome bottlenecks in carrier harvesting. Here, we present a theoretical and computational framework, Non-Equilibrium Scattering in Space and Energy (NESSE), to predict the spatial evolution of carrier energy distributions that combines the best features of phase-space (Boltzmann) and particle-based (Monte Carlo) methods. Within the NESSE framework, we bridge first-principles electronic structure predictions of plasmon decay and carrier collision integrals at the atomic scale, with electromagnetic field simulations at the nano- to mesoscale. Finally, we apply NESSE to predict spatially-resolved energy distributions of photo-excited carriers that impact the surface of experimentally realizable plasmonic nanostructures at length scales ranging from tens to several hundreds of nanometers, enabling first-principles design of hot carrier devices.
The ability to harness light-matter interactions at the few-photon level plays a pivotal role in quantum technologies. Single photons - the most elementary states of light - can be generated on-demand in atomic and solid state emitters. Two-photon states are also key quantum assets, but achieving them in individual emitters is challenging because their generation rate is much slower than competing one-photon processes. We demonstrate that atomically thin plasmonic nanostructures can harness two-photon spontaneous emission, resulting in giant far-field two-photon production, a wealth of resonant modes enabling tailored photonic and plasmonic entangled states, and plasmon-assisted single-photon creation orders of magnitude more efficient than standard one-photon emission. We unravel the two-photon spontaneous emission channels and show that their spectral line-shapes emerge from an intricate interplay between Fano and Lorentzian resonances. Enhanced two-photon spontaneous emission in two-dimensional nanostructures paves the way to an alternative efficient source of light-matter entanglement for on-chip quantum information processing and free-space quantum communications.
Ultra-short pulses with high repetition frequency have great application prospects in the field of nano-optics. Here, in the case of continuous wave incidence, the femtosecond pulses with THz repetition frequency are achieved in the transmission system consisting of a rectangular cavity, a V-groove (VG) cavity and a nanowire embedded with quantum emitters (QEs). The generation mechanism of the ultra-short pulses with high repetition frequency is elucidated by semi-classical Dicke model. Attribute to the presence of the two-level QEs, the field amplitude in plasmonic resonator is oscillating with time, resulting in the transmittance of the system behave as the form of pulse oscillation. Moreover, The pulse repetition frequency and extinction ratio can be freely controlled by the incident light intensity and QEs number density to obtain the required ultra-short pulses at nanoscale, which also has potential applications in optical computing.
Promoting performance of generation and transport of hot carriers in metal/semiconductor junctions is critical for harvesting energy of hot carriers. However, the low injection efficiency of hot carriers generated in the commonly used noble metals such as Au hinder the applications of hot-carrier devices. Here, we proposed that metallic TiN might be a better plasmonic material than the noble metals for generating and transporting hot carriers, based on first-principles calculations and Monte Carlo simulations. For the TiN/TiO2 junction, the concentration of hot carriers near the Fermi level is high, the lifetime and mean free path of the hot carriers are long, and the injection efficiency is large. The optimal injection efficiency could be achieved in a core/shell cylindrical TiN/TiO2 junction with the thickness of TiN ~ 5 nm and the incident photon energy ~ 0.6 eV.
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