Search results for "Absorption"
showing 10 items of 2701 documents
The electronic structure of zircon-type orthovanadates: Effects of high-pressure and cation substitution
2012
The electronic structure of four ternary-metal oxides containing isolated vanadate ions is studied. Zircon-type YVO4, YbVO4, LuVO4, and NdVO4 are investigated by high-pressure optical-absorption measurements up to 20 GPa. First-principles calculations based on density-functional theory were also performed to analyze the electronic band structure as a function of pressure. The electronic structure near the Fermi level originates largely from molecular orbitals of the vanadate ion, but cation substitution influence these electronic states. The studied ortovanadates, with the exception of NdVO4, undergo a zircon-scheelite structural phase transition that causes a collapse of the band-gap energ…
Analytic JV-Characteristics of Ideal Impurity PV-Cells
2017
In this article the mathematical modeling of idealized impurity photovoltaic cells is greatly simplified through the derivation of analytic JV-characteristics. The resulting expressions are also facilitating the intuitive understanding of such photovoltaic devices. The new model is used to investigate the sensitivity of impurity photovoltaic cells to the absorption band width, the impurity related absorptivity and the external radiative efficiency. It is found that impurities with narrow absorption bands or low absorptivity can greatly reduce the efficiency of the device, even if they are fully radiative and have energy levels situated at optimal positions in the band gap. It is also found …
Synthesis of cubic and hexagonal NaYF4:Er3+
2012
Up-conversion luminescence process, which is related to absorption of several light photons (usually infrared) followed by emission of light in the visible or even ultraviolet spectral regions, has attracted interest of scientists due to its potential practical use in various applications including biolabels, temperature sensors, light sources etc. Although observable in d- and f-ions doped materials, the highest efficiency of up-conversion luminescence is usually attained in lanthanides doped hosts. Among huge variety of materials suitable as up-conversion hosts the most prominent is considered to be NaYF4, both due to its low phonon energy and multisite nature of the crystalline lattice. …
Mass absorption indices of various types of natural aerosol particles in the infrared
2010
The mass absorption index of aerosol particles has been measured in the 2-17-microm wavelength region. The measurements were performed on films of aerosol particles that were collected by an automatic jet impactor at polluted and various uncontaminated remote sites. All but marine aerosols possess strong absorption bands in the transparent part of the atmospheric long-wave spectrum, indicating marked influence of aerosol particles on the radiation budget of the atmosphere.
Physicochemical properties of Ru(bpy)32+ entrapped in silicate bulks and fiber thin films prepared by the sol–gel method
1999
Silicate porous xerogels doped with ruthenium bipyridine (Ru(bpy)32+) complex have been obtained in the bulk form and in thin films on optical fibers. The hypsochromic shifts in the absorption and emission maxima are accompanied by fourfold increase in the lifetimes of the entrapped complex. The temperature-dependent lifetimes reveal that silicate xerogels induce two competing thermally activated processes in the excited state decay of the immobilized complex. The excited state lifetimes of the doped bulk xerogels and the fibers coated with thin films containing Ru(bpy)32+ are virtually identical to those obtained for the fibers coated with additional gas-impermeable layers.
Laser ablation of a turbid medium : Modeling and experimental results.
2006
International audience; Q -switched Nd:YAG laser ablation of a turbid medium (paint) is studied. The optical properties (absorption coefficient, scattering coefficient, and its anisotropy) of a paint are determined with a multiple scattering model (three-flux model), and from measurements of reflection-transmission of light through thin layers. The energy deposition profiles are calculated at wavelengths of 532 nm and 1.064 $\mu$m. They are different from those described by a Lambert-Beer law. In particular, the energy deposition of the laser beam is not maximum on the surface but at some depth inside the medium. The ablated rate was measured for the two wavelengths and compared with the en…
Dopants and defects: local structure and dynamics in barium cerates and zirconates
2010
In this paper we present an overview of state-of-the-art EXAFS measurements and data analysis on Ba, Ce, Zr, Y, In and Gd local environments in Y:BaCeO3, In:BaCeO3, Gd:BaCeO3, Y:BaZrO3, and In:BaZrO3, at different temperatures, hydration degrees and doping levels. This approach allows to reach unprecedented insights on the peculiar role of the dopant, and its interactions with the other lattice defects. In particular, we evidence that each different dopant shows unique behavior, depending mainly on its electronic structure, and that the usual criterion of ionic radius matching is not useful to outline an effective doping strategy of proton-conducting perovskites. As what concerns the struct…
Third-order nonlinear optical effects of silver nanoparticles and third harmonic generation from their plasma plumes
2021
Abstract We investigated the third-order nonlinear optical (NLO) properties of the silver (Ag) nanoparticles (NPs) of various sizes, which were produced by disintegration of commercially available 20 and 100 nm NPs in different solvents. It is observed that NPs with the sizes less or greater than 30 nm possess saturable absorption or reverse saturable absorption (or two-photon absorption), respectively. The NPs suspensions show a self-focusing effect. In addition, the third harmonic generation from the plasma plumes produced by nanosecond laser ablation of bulk Ag and Ag NPs of 100 nm and 20 nm sizes is reported. The third harmonic efficiency from the plasmas containing NPs was higher compa…
Luminescence properties of KNbO3 crystals
1997
Thermostimulated luminescence, X-ray-induced luminescence, photostimulated luminescence as well as the time-resolved luminescence and absorption after pulsed electron beam irradiation were studied in KNbO3 crystals at 80–400 K. A correlation between defects causing the luminescence and blue-light-induced IR absorption effects supressing the second harmonic generation efficiency in KNbO3 is discussed.
Raman and IR investigation of silica nanoparticles structure
2013
Abstract In the present investigation we report experimental data regarding the Raman and Infra-Red (IR) absorption activities of commercial silica nanoparticles. We compared the data of the nanoparticles with the ones acquired in the same experimental conditions for commercial bulk silica. By this comparison we highlighted that the variability of the spectral features of the matrix related Raman and IR bands in the nanoparticles is above the one observed for the bulk systems before any treatments. Furthermore, by studying nanoparticles with different sizes (diameters from 40 to 7 nm) and applying the shell-model we can suggest that the core network of the nanoparticles is close to the one …