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In this study, the light propagation in a structure consisting of S i O x on Si substrate with Al nanoparticles regularly placed in the S i O x layer is considered. Numerical modelling is performed by solving the Maxwell equations for the electromagnetic waves. In distinction from the well-known finite-difference time-domain (FDTD) simulation technique, we do not solve time-dependent wave equations here; rather, we propose a new numerical technique. This technique allows us to determine the stationary amplitudes of the electromagnetic oscillations directly from the linear algebraic equation system. The obtained results apply to silicon solar cells with an S i O x + Al top layer to maximise their efficiency. We found that 26 nm and 39 nm diameters of spherical Al nanoparticles are nearly optimal for a λ = 435.8 nm wavelength of the incident light. In addition, we evaluated the (nearly) optimal parameters of their placement in the S i O x layer. The results show the possibility of increasing the efficiency of solar cells by increasing the light absorption inside the active Si layer from ≈60% to ≈80%. Future perspectives on the proposed method and its possible applications are discussed. [ABSTRACT FROM AUTHOR]

We study a quantum cone, a novel structure composed of multiple quantum dots with gradually decreasing diameters from the base to the top. The dot distribution leads to a dispersive radiated spectrum. The blue edge of the spectrum is determined by the quantum confinement of excitons on top of the cones, while the red edge is determined by the bandgap of a semiconductor. We observe the kinetics of photoluminescence by obeying the stretch-exponential law from quantum cones formed on the surface of diamond-like carbon (DLC). They are explained by an increase in the lifetime of excitons along the height of the cone from the top to the base of the cone and an increasing concentration of excitons at the base due to their drift in the quasi-built-in electric field of the quantum cone. The possible visualization of the quantum cone tops of DLC using irradiation by a UV light source is shown. A quantum cone is an innovative nano-source of light because it substitutes for two elements in a conventional spectrometer: a source of light and a dispersive element—an ultrafast monochromator. These features enable the building of a nano-spectrometer to measure the absorbance spectra of virus and molecule particles. [ABSTRACT FROM AUTHOR]

A quantum prism, a new structure, consisting of many quantum wires with a diameter that gradually decreases from the base to the top, is the focus of our research. This distribution of quantum wires leads to a dispersive emitted spectrum. The red edge of the spectrum is determined by the band gap width of the bulk semiconductor, and the blue edge is determined by the quantum size of the excitons at the top of the prism. The PL spectrum of the silicon prismatic sample was excited by weak and strong light absorption. At weak absorption (hνex = 1.2 eV), the PL spectrum is located in the visible part of the spectrum, from 1.4 eV to 1.9 eV, with an energy higher than the band gap of the Si crystal. Such a "blue shift" of PL spectra by 0.7 eV is characteristic of the quantum confinement effect. It is a rainbow spectrum with an optical upconversion. The quantum prism is a new type of nano light source, as it replaces two elements in a conventional spectrometer: a light source and a dispersive element. These features enable to create a nano-spectrometer for measuring the absorption spectrum of individual molecules or viruses. [ABSTRACT FROM AUTHOR]

We investigated the formation of graphite nanocrystals covered with graphite oxide for white light generation. The nanoparticles were formed using cost-efficient oxidation of a carbon-based dye pigment at different temperatures and verified using X-ray diffraction and Raman measurements. Formation of the graphite nanoparticles via thermal annealing was observed, while their light emission increased at higher oxidation temperatures. This was associated with a higher amount of oxygen defect groups. The time-resolved photoluminescence measurements showed linearly faster decays at shorter wavelengths and similar decays at different annealing temperatures. Broadband and linear vs. excitation emission spectra of the particles were found to be suitable for white-light-emitting devices and phosphor markers. The fast photoluminescence decay opens the possibility for the application of nanoparticles in optical wireless communication technology. [ABSTRACT FROM AUTHOR]

The development of new technology, which would be able to shift photosensitivity of Si devices to the mid-infrared range, preserving the benefits of cheap silicon readout circuits, is of high priority for short-wave infrared photo-detection in defense, medical, night vision, and material production applications. Group IV GeSn-based materials have recently shown promising optoelectronic characteristics, allowing extension of the detection range to the mid-infrared region. However, the electronic properties of the material are not well understood and need further research. In this work, we provide temperature dependent studies of carrier lifetime, diffusion coefficient, and diffusion length in Ge0.95Sn0.05 epilayer on silicon by applying contactless light induced transient grating technique. The observed temperature dependence of lifetime was explained by the recombination of carriers on vacancy-related defects. The electron and hole capture cross sections were calculated. The temperature dependence of the diffusion coefficient indicated hole mobility limited by phonon and defect scattering. Weakly temperature dependent diffusion length of ∼0.5 μm verified material suitability for efficient submicrometer-thick optoelectronic devices. [ABSTRACT FROM AUTHOR]

A comparative analysis of the features of UV-stimulated emission (SE) of various disordered active materials based on ZnO crystallites for a random laser (RL) was carried out. The superlinear increase in the intensity of the UV photoluminescence (PL) band of polydisperse nano-micro-crystalline (PNMC) ZnO powder at a wavelength of λ = 387 nm and some narrowing of its halfwidth in the range of 20–15 nm with increasing pump intensity indicates random lasing with incoherent feedback (FB). The properties of similar UV PL bands under the same conditions of a thin film containing hexagonal ZnO microdisks, as well as samples of monodisperse ZnO nanopowder with nanoparticle sizes of 100 nm, indicate stimulated radiation with coherent feedback. It is shown that, among the studied materials, PNMC ZnO powder with widely dispersed crystallites ranges in size from 50 nm to several microns, which in turn, consists of nanograins with dimensions of ~25 nm, is the most suitable for creating a random laser with incoherent feedback at room temperature. The dominant factor of UV SE in PNMC ZnO powder is radiation transitions under exciton–exciton scattering conditions. The possible mechanisms of this random emission with the continuous spectrum are discussed. The average optical gain coefficient αg at λ = 387 nm in this RL system is estimated as αg~150 cm−1. [ABSTRACT FROM AUTHOR]

Photoluminescence of composites containing carbon nanostructures is critical for many modern applications. Of particular significance are metamaterials capable of generating white light photoluminescence within a single structure, as the white luminescence usually needs separate red–green–blue emitters. This work provides an insight into the photoluminescent properties of a promising family of hierarchical metamaterials made of carbon nanocones in a silicon oxide matrix in view of their use as efficient single-layer white light emitters. The composites were prepared using a facile plasma-enhanced technology, followed by a thermal treatment. ATR-FTIR, Raman, SEM, and AFM microscopy and profilometry characterization confirmed the presence of silica and carbon nanocones. The advanced comprehensive photoluminescence studies conducted using solid-state Yb:KGW laser revealed a significant difference in photoluminescent properties for the composites containing sharp nanocones of similar parameters. A comprehensive morphological analysis performed using several analytical techniques including the 2D fast Fourier transform spectra, Hough distributions, spectral density function, and Minkowski functionals revealed the Minkowski boundary functional, ordering, and connectivity to be the most important morphological descriptors for the photoluminescent response. This study suggests that these morphological parameters play a critical role in defining the key properties of advanced metamaterials via the overlap of Ψ functions and may therefore be targeted for informed material design and intelligent fabrication. [ABSTRACT FROM AUTHOR]

Zn nanoparticles characteristics like size and concentration can be tailored by laser irradiation. A pulsed Nd:YAG laser was operated at a wavelength of 266 nm, pulse duration of 3 ns, and a maximum intensity of 315.0 MW cm−2. Zinc nanoparticles formation is proposed to occur in two stages. In the first stage, Zn interstitials (Zni) are generated at the irradiated site. In the second stage, Zni agglomerate to increase the size of Zn nanoparticles up to 120 nm. Zni formation is implied from an increase in the electrical conductivity, but agglomeration occurs from heat treatment provided by laser irradiation. Single laser pulse irradiation creates small nanoparticles about 7 nm in size. Further laser pulses reduces the concentration of small nanoparticles and increases the size of nanoparticles up to 120 nm. The size and structure was observed by field emission scanning electron microscope and Raman spectroscopy. Topography and electrical conductivity was mapped by atomic force microscopy. [ABSTRACT FROM AUTHOR]