Region Of Electromagnetic Radiation Research Articles

Characterizations of Galena as Potential Photosensitizer in a Natural Dye-Sensitized Solar Cell

Dye is one of the principal parts for high power conversion efficiency in a Dye-Sensitized Solar Cell. Conspicuous developments have taken place via the work of several researchers in the engineering of novel dye structures so as to enhance the performance of the system. The properties of a natural mineral dye were studied in this work. The structure of the dye was determined and discovered to have contains constituents that could enhance better absorption of solar radiation for use in a Dye-Sensitized Solar Cell (DSSC). The Lead sulphide and iron content of the mineral dye studied as revealed by the X-Ray diffraction analysis done suggest this. The X-Ray Fluorescence (XRF) done revealed that the concentration of Lead and Iron (Fe) is high as compared to other elements present in the material, probably as a result of the fact that it is a geological sample (of the earth) and which may even suggest its colour and hence makes it absorbs solar radiation of visible region at its wavelength (around 380 nm – 800 nm). The functional groups present in the dye as obtained from the Fourier transform infrared spectroscopy are the Amine, Carbonyl, and hydroxyl groups, all of which confirm the suitability of the dye material in photosensitizing a semiconductor in a DSSC. The absorption spectra of the dye within the visible region of electromagnetic radiation show that the material has high, increased, and stable absorption of visible light which is suggesting a more durable natural dye for a DSSC than the easily degraded natural dyes of plants source.

Effects of Ni-doping on the photo-catalytic activity of TiO2 anatase and rutile: Simulation and experiment

The Ni impurity has an inconsistent impact on the photo-catalytic activity of TiO2 in different regions of electromagnetic radiation. In this work, the effect of different concentrations of Ni doping into anatase and rutile TiO2 structures is investigated theoretically and experimentally. Doubling the concentration of doped Ni does not change the photo-catalytic activity of TiO2 significantly according to photo-degradation of Acid Blue 92 (AB 92) under ultra violate and visible (UV–Vis) lights. However, increment of the dopant concentration enhances the thermodynamic yield of TiO2 crystalline structure (i.e. rutile) at low temperature calcination of TiO2. Density functional theory (DFT) calculations also confirm the impact of Ni impurity on the higher stability of rutile phase. Computational geometry optimization favors a heterogeneous distribution of Ni atoms in 12.5 at% Ni-TiO2, that is verified by a broad impurity peak inside the band gap of TiO2 in UV–Vis diffuse reflectance spectrum (UV–Vis DRS). The DRS and DFT results denote a negligible change in the band gap energy of TiO2 compared to Ni-TiO2. Based on DFT results, generation of defect states gives rise to photo-catalytic activities of Ni-TiO2 in the invisible region. However, adding Ni to anatase TiO2 changes the type of the band gap from indirect to direct and reduces its photo-efficiency in the degradation of AB 92 under UV irradiation. In addition, a positive shift of the valance and conduction band edges of TiO2 occurs after Ni doping, which reduces the photo-oxidation activity of TiO2.

Optical properties of one-dimensional photonic crystals obtained by micromatchining silicon (a review)

The theoretical and experimental investigations of photonic band gaps in one-dimensional photonic crystals created by micromatchining silicon, which have been performed by the author as part of his doctoral dissertation, are presented. The most important result of the work is the development of a method of modeling photonic crystals based on photonic band gap maps plotted in structure–property coordinates, which can be used with any optical materials and in any region of electromagnetic radiation, and also for nonperiodic structures. This method made it possible to realize the targeted control of the optical contrast of photonic crystals and to predict the optical properties of optical heterostructures and three-component and composite photonic crystals. The theoretical findings were experimentally implemented using methods of micromatchining silicon, which can be incorporated into modern technological lines for the production of microchips. In the IR spectra of a designed and a fabricated optical heterostructure (a composite photonic crystal), extended bands with high reflectivities were obtained. In a Si-based three-component photonic crystal, broad transmission bands and photonic band gaps in the middle IR region have been predicted and experimentally demonstrated for the first time. Si–liquid crystal periodic structures with electric-field tunable photonic band-gap edges have been investigated. The one-dimensional photonic crystals developed based on micromatchining silicon can serve as a basis for creating components of optical processors, as well as highly sensitive chemical and biological sensors in a wide region of the IR spectrum (from 1 to 20 μm) for lab-on-a-chip applications.

Influence of the defect state of samples on the luminescence spectra of CdS single crystals irradiated by electrons

The photoluminescence spectra of CdS single crystals irradiated by electrons (E = 1.2 MeV, Φ = 2×1017 cm−2) are investigated in the visible and near-infrared regions of electromagnetic radiation. Some samples of the CdS single crystals are preliminarily irradiated by neutrons (E = 2 MeV, Φ = 2 × 1018 cm−2) with the aim of increasing the concentration of initial structural defects. From analyzing the peak intensities of photoluminescence in the irradiated single crystals at the wavelengths λm = 0.720, 1.030, and 0.605 μm, it is concluded that the CdS samples with a low concentration of structural defects in the initial state possess the highest resistance to electron radiation. It is assumed that the observed transformation of the photoluminescence spectra of the imperfect CdS single crystals subjected to electron irradiation is determined by either the mechanisms of subthreshold defect formation or the transformation of the defect complexes in elastic and electric fields near the large structural damages of the crystal lattice.