Search results for "Quantum dot"
showing 10 items of 418 documents
Sub-critical InAs layers on metamorphic InGaAs for single quantum dot emission at telecom wavelengths
2014
We report on the design, the growth by MBE and the optical and morphological characterization of metamorphic InAs/InGaAs quantum dots (QD) with a density low enough to allow single dot characterization without the need of complex litographic steps to isolate single QDs. InAs sub-critical coverages were deposited on InxGa1-xAs metamorphic buffers (MBs) and the transition from 2D growth to 3D island nucleation was monitored by reflection high energy electron diffraction (RHEED). We discuss the fundamental differences of the sub-critical growth method compared with the Stranski-Krastanow one, also by considering available theoretical models. AFM confirmed that the density of QDs can be control…
Size-And Wavelength-Dependent Two-Photon Absorption Cross-Section of CsPbBr3 Perovskite Quantum Dots
2017
All-inorganic colloidal perovskite quantum dots (QDs) based on cesium, lead, and halide have recently emerged as promising light emitting materials. CsPbBr3 QDs have also been demonstrated as stable two-photon-pumped lasing medium. However, the reported two photon absorption (TPA) cross sections for these QDs differ by an order of magnitude. Here we present an in-depth study of the TPA properties of CsPbBr3 QDs with mean size ranging from 4.6 to 11.4 nm. By using femtosecond transient absorption (TA) spectroscopy we found that TPA cross section is proportional to the linear one photon absorption. The TPA cross section follows a power law dependence on QDs size with exponent 3.3 +- 0.2. The …
Color Tuning and White Light by Dispersing CdSe, CdTe, and CdS in PMMA Nanocomposite Waveguides
2013
In this paper, active nanocomposite waveguides based on the dispersion of CdS, CdTe, and CdSe colloidal quantum dots (QDs) in PMMA are proposed. Their propagation properties are studied as a function of the concentration of nanoparticles in the polymer using the variable length stripe method. When the three nanostructures are dispersed in the same film, the structure is able to waveguide the three basic colors: red (CdSe), green (CdTe), and blue (CdS), it being possible to engineer any waveguided color by an appropriate choice of the filling factor of each QD in the PMMA matrix. For this purpose, it is important to take into account reabsorption effects and the Förster energy transfe…
Photovoltaic module characteristics from CIGS solar cell modelling
2013
We describe our approach to the task of modelling, both at single cell structure and complete module levels, during the solar cell technology development process. This can give very helpful indications, in terms of global photovoltaic module characteristics, for the assessment of intermediate research results and planning of further experiments. We make reference specifically to the fabrication of thin film CIGS solar cells by means of single-step electrodeposition, a technique which appears fairly easy and low-cost but, at the same time, can lead to quite different structural and electrical properties.
Quantum dots functionalised artificial peptides bioinspired to the D1 protein from the Photosystem II of Chlamydomonas reinhardtii for endocrine disr…
2021
Herein we describe the design and synthesis of novel artificial peptides mimicking the plastoquinone binding niche of the D1 protein from the green photosynthetic alga Chlamydomonas reinhardtii, also able to bind herbicides. In particular, molecular dynamics (MD) simulations were performed to model in silico the behaviour of three peptides, D1Pep70-H, D1Pep70-S264K and D1Pep70-S268C, as genetic variants with different affinity towards the photosynthetic herbicide atrazine. Then the photosynthetic peptides were functionalised with quantum dots for the development of a hybrid optosensor for the detection of atrazine, one of the most employed herbicides for weed control in agriculture as well …
Si:O Alloys for Photovoltaics: Optical and Electrical Properties from Quantum Dots to Thin Films
2010
In current Si based PV devices the sun-light-electricity conversion rarely exceeds the 20% in efficiency, stimulating significant efforts towards new solutions and technologies for giving a boost to Si for PV. One of the most promising routes for the 21st century is exploiting the quantum confinement effect in reduced dimensionality systems, with the aim to harvest the full solar spectrum. Recently, it has been proposed that a certain modulation of the optical bandgap (EG OPT) can be attained by changing the size of Si quantum dots (QDs), which should allow for a large absorption of the solar photon flux [1]. By this way, an all-Si tandem solar cell could be fabricated, by stacking solar …
Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds
2008
We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers in silica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which we ascribe to the departure from the Frank-Condon region of the first excited singlet state in 240 fs, followed by cooling in ∼10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramolecular vibrat…
Influence of dissipative tunneling on the photodielectric effect associated with the excitation of impurity complexes A+ + e in a quasi-zero-dimensio…
2022
Effect of tunneling decay for the quasi-stationary A+-state, in an impurity complex A+ + e (a hole, localized on a neutral acceptor, interacting with an electron, localized in the ground state of a quantum dot) on the photodielectric effect, associated with the excitation of impurity complexes A+ + e in a quasi-zero-dimensional structure, has been studied in the zero-radius potential model in the one-instanton approximation. Calculation of the binding energy of a hole in an impurity complex A+ + e was performed in the zero radius potential model in the adiabatic approximation. It is shown that as the probability of dissipative tunneling increases, the binding energy of a hole in a complex A…
Resonant hyper-Raman scattering in spherical quantum dots
1998
A theoretical model of resonant hyper-Raman scattering by an ensemble of spherical semiconductor quantum dots has been developed. The electronic intermediate states are described as Wannier-Mott excitons in the framework of the envelope function approximation. The optical polar vibrational modes of the nanocrystallites (vibrons) and their interaction with the electronic system are analized with the help of a continuum model satisfying both the mechanical and electrostatic matching conditions at the interface. An explicit expression for the hyper-Raman scattering efficiency is derived, which is valid for incident two-photon energy close to the exciton resonances. The dipole selection rules f…
Magnetic field dependence of quantum dot ground states
2008
We study the ground states of a planar quantum dot with N = 5,6,7 electrons, in the presence of a perpendicular magnetic field. Using a spatially unrestricted Hartree Fock technique followed by spin and angular momentum symmetry restoration, chemical potentials are calculated and transitions between different ground states are identified. A spin blockade in the 6 -> 7 transition is found. The structure of the quantum dot wave functions is illustrated by their electron densities. (c) 2007 Elsevier B.V. All rights reserved.