Search results for "Physics::Optics"
showing 10 items of 1958 documents
Photoionization of metal clusters.
1996
The photoionization cross section of metal clusters is studied using simple theoretical models. In the case of small clusters, the plasmon is well below the photoionization threshold and the photoionization is dominated by simple independent-particle processes: One electron absorbs all the energy of the photon and immediately leaves the cluster. For large sodium clusters the photoionization efficiency curve is a result of a two-step process: First, the photon excites a plasmon and then the plasmon decays, either by emitting a photoelectron or by heating the cluster. A simple expression for the photoionization cross section near the threshold is derived. \textcopyright{} 1996 The American Ph…
Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites
2016
Semiconductor nanocrystals have arisen as outstanding materials to develop a new generation of optoelectronic devices. Their fabrication under simple and low cost colloidal chemistry methods results in cheap nanostructures able to provide a wide range of optical functionalities. Their attractive optical properties include a high absorption cross section below the band gap, a high quantum yield emission at room temperature, or the capability of tuning the band-gap with the size or the base material. In addition, their solution process nature enables an easy integration on several substrates and photonic structures. As a consequence, these nanoparticles have been extensively proposed to devel…
Photoluminescence of Si nanocrystals embedded in SiO2: Excitation/emission mapping
2014
Time-resolved photoluminescence from Si nanocrystals produced by 1100∘C thermal annealing of SiOx/SiO2 multilayers were investigated by tunable laser excitation, achieving a detailed excitation/emission pattern in the visible and UV range. The emission lineshape is a gaussian curve inhomogenously broadened because of the size distribution of Si nanocrystals, the excitation spectrum consists of the overlap of two gaussian bands centered around 3.4 and 5.1 eV. The mapping of luminescence spectral components with the lifetime points out the energy cubic dependence of the spontaneous emission rate. These findings are interpreted on the basis of models proposed in literature that associate this …
Valence-band splitting energies in wurtzite InP nanowires : Photoluminescence spectroscopy and ab initio calculations
2010
We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, r…
Plasmon-induced slow aging of exciton generation and dissociation for stable organic solar cells
2016
Fast degradation is a major issue with organic photovoltaics (OPVs). Integrating plasmonics with OPVs has improved their efficiency; however, the stability effects are unknown. We demonstrate that plasmonic effects can improve the lifetime and efficiency. The aging effects on charge carrier generation and transport are investigated. Confocal time-resolved photoluminescence of Au nanoparticle (NP) doped polymer blend was performed to understand the plasmonic effects on excited-state dynamics. Hot exciton generation is observed directly at the Au-NP surface, which contributed to achieving a nearly perfect exciton dissociation yield. We found that slow aging of the plasmonic effect and the hot…
Photoluminescence spectral dispersion as a probe of structural inhomogeneity in silica
2011
We perform time-resolved photoluminescence measurements on point defects in amorphous silicon dioxide (silica). In particular, we report data on the decay kinetics of the emission signals of extrinsic oxygen deficient centres of the second type from singlet and directly excited triplet states, and we use them as a probe of structural inhomogeneity. Luminescence activity in sapphire (alpha-Al(2)O(3)) is studied as well and used as a model system to compare the optical properties of defects in silica with those of defects embedded in a crystalline matrix. Only for defects in silica did we observe a variation of the decay lifetimes with emission energy and a time dependence of the first moment…
Engineering light emission of two-dimensional materials in both the weak and strong coupling regimes
2017
Abstract Two-dimensional (2D) materials have promising applications in optoelectronics, photonics, and quantum technologies. However, their intrinsically low light absorption limits their performance, and potential devices must be accurately engineered for optimal operation. Here, we apply a transfer matrix-based source-term method to optimize light absorption and emission in 2D materials and related devices in weak and strong coupling regimes. The implemented analytical model accurately accounts for experimental results reported for representative 2D materials such as graphene and MoS2. The model has been extended to propose structures to optimize light emission by exciton recombination in…
Light-Driven Extremely Nonlinear Bulk Photogalvanic Currents
2021
We predict the generation of bulk photocurrents in materials driven by bichromatic fields that arc circularly polarized and corotating. The nonlinear photocurrents have a fully controllable directionality and amplitude without requiring carrier-envelope-phase stabilization or few-cycle pulses, and can be generated with photon energies much smaller than the band gap (reducing heating in the photoconversion process). We demonstrate with ab initio calculations that the photocurrent generation mechanism is universal and arises in gaped materials (Si, diamond, MgO, hBN), in semimetals (graphene), and in two- and three-dimensional systems. Photocurrents are shown to rely on sub-laser-cycle asymme…
Determining the optical properties of adsorbate covered surfaces by dichroism in VUV-photoemission
1999
The dichroic effects of photoemission excited by polarised light depend on the angle of photon incidence. Measurements of the difference in the angle-resolved photoemission intensities from Cs 5p semi-corelevels excited by photons of opposite helicity, or of orthogonal linear polarisation are reported. It was thought that the dependence of dichroism on the angle of incidence cannot be described using equations omitting metal optics. A complete consideration of the vector potential of the exciting light is needed, including the phase shift between it's parallel and perpendicular components. The phase shift is produced by the complex index of refraction. Using the Fresnel equations for struct…
Unconditional generation of bright coherent non-Gaussian light from exciton-polariton condensates
2012
Exciton-polariton condensates are considered as a deterministic source of bright, coherent non-Gaussian light. Exciton-polariton condensates emit coherent light via the photoluminescence through the microcavity mirrors due to the spontaneous formation of coherence. Unlike conventional lasers which emit coherent Gaussian light, polaritons possess a natural nonlinearity due to the interaction of the excitonic component. This produces light with a negative component to the Wigner function at steady-state operation when the phase is stabilized via a suitable method such as injection locking. In contrast to many other proposals for sources of non-Gaussian light, in our case, the light typically …