Region Of Electromagnetic Spectrum Research Articles

The structural, electronic, magnetic and optical properties of the new promising spintronic material Bi0.92Tb0.08FeO3: A first-principles approach

With a view to obtain high performance multiferroic devices for applications in data storage media and multiple storage memories, we have investigated the multiferroic properties of Bi0.92Tb0.08FeO3 for the first time based on density functional theory calculations. Our results on Bi0.92Tb0.08FeO3 reveal the presence of incommensurate band gaps in the up and down spin channels and thus confirm the existence of bipolar magnetic semiconductor, a rare and promising candidate among spintronic materials. The hybridization between Bi, Tb 6s states and O 2p states gives rise to cation off-centering and distortion and the partial density of states indicates the presence of exchange splitting of Fe 3d states. In addition, we have also obtained a ferrimagnetic arrangement of Fe atoms as a result of destruction of the antiferromagnetic spin structure. Accounting for optical properties, when electric field is perpendicular with respect to the crystallographic c axis (E⊥c) the maximum value of refractive index reached to 3.3 at 3.3 eV (375.7 nm, UV region) and 3.3 at 2.5 eV (496 nm, visible region). This is one of the largest values of refractive index known in the visible region of electromagnetic spectrum and thus Bi0.92Tb0.08FeO3 can become a promising candidate for optical communication devices. Also the dielectric constant reaches maximum to 10.6 at 2.5 eV (496 nm, visible region) for E⊥c and 10.5 at 3.3 eV (375.7 nm, UV region). A high polarization value 82.56 µC/cm2 was calculated for Bi0.92Tb0.08FeO3 and is in good agreement with the known experimental values.

Preparation and spectroscopic analysis of zinc oxide nanorod thin films of different thicknesses

AbstractZinc oxide thin films with different thicknesses were prepared on microscopic glass slides by sol-gel spin coating method, then hydrothermal process was applied to produce zinc oxide nanorod arrays. The nanorod thin films were characterized by various spectroscopic methods of analysis. From the images of field emission scanning electron microscope (FESEM), it was observed that for the film thickness up to 200 nm the formed nanorods with wurtzite hexagonal structure were uniformly distributed over the entire surface substrate. From X-ray diffraction analysis it was revealed that the thin films had good polycrystalline nature with highly preferred c-axis orientation along (0 0 2) plane. The optical characterization done by UV-Vis spectrometer showed that all the films had high transparency of 83 % to 96 % in the visible region and sharp cut off at ultraviolet region of electromagnetic spectrum. The band gap of the films decreased as their thickness increased. Energy dispersive X-ray spectroscopy (EDS) showed the presence of zinc and oxygen elements in the films and Fourier transform infrared spectroscopy (FT-IR) revealed the chemical composition of ZnO in the film.

Investigations on electrical and optical properties of samarium chloride coordinated urea-thiourea semi-organic complex

ABSTRACTSamarium chloride coordinated urea-thiourea semi-organic complex was prepared at room temperature by slow evaporation technique. The complexes were prepared with high degree of crystallinity. The unit cell parameters determined by powder X-ray diffraction reveals the complex to be having orthorhombic system with Pnma space group. The dielectric measurements were made by impedance spectroscopy and various dielectric parameters were studied as a function of temperature and frequency. The ac conductivity is governed by Arrhenius type behaviour and universal power law. In optical analysis, the transmittance characteristics of complexes were studied in ultra-violet and visible region of electromagnetic spectrum.

Benign Synthesis of Black Microspheres of Anatase TiO2 with Paramagnetic Oxygen Vacancies through NH3 Treatment.

Coloured TiO2 is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres (B-TiO2 ) through a two-step process is reported. In the first step, amorphous white TiO2 microspheres (W-TiO2 ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W-TiO2 is thermally annealed at 500 °C to obtain B-TiO2 . The diffuse reflectance analysis showed that B-TiO2 absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B-TiO2 that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single-electron-trapped (or paramagnetic) oxygen vacancies (Vo ⋅) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins.

Synthesis of MoS2 Quantum Dots Uniformly Dispersed on Low Dimensional MoS2 Nanosheets and Unravelling its Multiple Emissive States

AbstractWe demonstrate a simple and green route for the synthesis of MoS2 quantum dots (QDs) of size 1‐4 nm dispersed uniformly over the mono and bilayered, low dimensional MoS2 sheets, referred as MoS2 quantum dots dispersed over nanosheets (MoS2 QDNS). The synthesis was accomplished by the high temperature hydrothermal reaction of bulk MoS2 in aqueous NaOH. The MoS2 QDNS displays luminescence emission spanning a large portion of the UV and visible region of electromagnetic spectrum, envisaged to stem from both QDs and the nanosheets. A detailed photophysical characterization including time resolved fluorescence were carried out to unfold the origin of photoluminescence (PL) emission from this hybrid nanostructure. Our studies reveal that, blue and red portion of the emission are solely from QDs and the nanosheets, respectively. Whereas intermediate segment of the emission hail from the synergistic contribution of QDs and nanosheets. The MoS2 QDNS, manifests excellent stability, retained its characteristic morphology and PL even after several months. Finally, the excellent pH responsive PL emission of MoS2 QDNS makes them a promising candidate for biological and environmental applications.

Theoretical investigation of optical properties and band gap engineering for Zn1−xTMxTe (TM = Fe, Co) alloys by modified Becke–Johnson potential**Project supported by the Deanship of Scientific Research at King Saud University (for Shahid M Ramay) (Grant No. RG 1435-004), the University of the Punjab, Lahore for financial support through Faculty Research Grant Program (for M Hassan), and the HEC Pakistan

The direct band gap ZnTe with transition metal (TM) impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke–Johnson (mBJ) functional for performing the structural computations and detailed investigations of the optical characters in (, Co) alloys with . By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for (, Co) have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with TM content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing TM concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.

Arsenic carbide monolayer: First principles prediction

Using the first principles calculation, a new pentagonal indirect band gap semiconductor namely arsenic carbide monolayer (As2C) is predicted. The calculated cohesive energy of −5.69eV/atom the thermodynamic stability of the predicted monolayer. Furthermore, the kinetic stability of the monolayer is examined by phonon dispersion calculation, where the absence of imaginary modes and high value of maximum phonon frequency confirms the high dynamic stability of the proposed monolayer. Investigating in the electronic properties of the As2C monolayer indicates that it is a semiconductor with an indirect band gap of 1.62eV. Analyzing the optical properties of the As2C monolayer imply that the monolayer has high UV light absorption, however, it has an almost zero absorption in visible region of electromagnetic spectra. The specific electronic and optical properties imply that As2C monolayer may be used in new generation of nano-optoelectronic technology design.

A comprehensive study of the optoelectronic properties of donor-acceptor based derivatives of 1,3,4-oxadiazole

A variety of 1,3,4-oxadiazole derivatives based on electron- donor pyrrole and -acceptor nitro groups are modelled. Various isomers of pyrole-oxadiazole-nitro unit and its dimer linked to substituted and unsubstituted phenyl group are studied using the dispersion corrected density functional theoretical method. The electron density distribution in frontier orbitals of the phenyl-spacer compounds bearing amino and phenylamino groups indicates the possibility of intramolecular charge transfer. The isomers of phenyl-spacer compounds absorb in visible region of electromagnetic spectrum. The compounds show high values of light harvesting efficiency, despite the weak anchoring nature of nitro groups.

Methylene Blue Photocatalytic Degradation under Visible Irradiation on In2S3 Synthesized by Chemical Bath Deposition

In this work, we synthesized In2S3 powder through chemical bath deposition method (CBD) in acid medium; we used thioacetamide as sulphide source and InCl3 as indium ion source. X-ray diffraction, diffuse reflection, and Raman spectroscopy measurements were used for In2S3 powder physicochemical characterization. Optical analysis indicated that In2S3 was active in the visible region of electromagnetic spectrum; it had a band gap of 2.47 eV; the diffraction patterns and Raman spectroscopy suggested that powder had polycrystalline structure. Furthermore, we also studied the adsorption process of methylene blue (MB) on In2S3 powder; adsorption studies indicated that the Langmuir model describes experimental data. Finally, photocatalytic degradation of MB was studied under visible irradiation in aqueous solution; besides, pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation; results indicated that the powder catalyst reduces 26% concentration of MB under visible irradiation.

Effect of ligands on crystallography, morphology and photo-catalytic ability of ZnS nanostructures

ZnS nanostructures have been synthesized using zinc complexes: Zn(ethyl xanthate)2] & [Zn(morpholine4-dithiocarbamate)2] from ligands potassium ethyl xanthate (KEX) and morpholine4-dithiocarbamate (MDTC) by solvothermal route of synthesis. Crystallographic and morphological analyses of synthesized ZnS nanostructures have been done by X-ray diffraction (XRD) and electron microscopy [Transmission Electron Microscope (TEM)], respectively. Diffraction and electron microscope studies reveal the formation of hexagonal structured ZnS nanocrystals of various morphologies (nanosheets & nanorods). UV–vis. absorption studies have been carried for the detailed optical analyses. Photoluminescence (PL) study was carried out to check luminescence of synthesized ZnS nanostructures in blue region of electromagnetic spectrum. It has been reported that the morphology of synthesized nanostructures strongly depends upon the precursor complexes prepared from two different classes of ligands; potassium ethyl xanthate and morpholine4-dithiocarbamate. Photo-catalytic activity potential of the synthesized ZnS nanostructures has been tested in UV light using methylene blue (MB) dye as a test contaminant in aqueous media. About 88.49% and 87.96% of MB dye was photo-degraded by ZnS nanostructures synthesized from Zn(EX)2 [ where EX stands for ethyl xanthate] and Zn(MDTC)2, respectively.

Broadband infrared response of sulfur hyperdoped silicon under femtosecond laser irradiation

Broadband infrared response has attracted great attention due to its potential applications in silicon based photodetectors. We have studied broadband infrared response of sulfur hyperdoped silicon under femtosecond laser irradiation. The fabricated PN photodiodes exhibit several photoresponse spectral peaks in near and mid-infrared region of electromagnetic spectrum. The onset energies corresponding to the distinct sub-band gap photoresponse features are consistent with the active energy levels of known sulfur within the silicon band-gap. This technique may offer a promising approach to fabricate low-cost broadband silicon based detectors.

γ irradiation induced effects on the TCO thin films

We report on gamma irradiation induced changes both in the optical and electrical properties of the Transparent Conductive Oxide (TCO) thin films. We used Co-60 radioisotope as a natural source of γ in our experiments. Applied total irradiation doses to the prepared samples change from 1 to 4kGy. The dose rate is kept finely constant at 200Gy/min. Optical transmissions in VIS-NIR region of electromagnetic spectrum and electrical conductivity (I-V) measurements on irradiated samples are conducted with respect to the total dose. Results show that regardless of the irradiation dose, there is no change in the current flow through the contacts on the TCO thin films after the irradiation. On the other hand, based on the on-line measurements, the current increases with the gamma irradiation and a threshold irradiation is detected in the optical properties of irradiated samples. Also, thin films are seen to preserve their initial amorphous structures at such a low irradiation doses according to XRD measurements. We propose that these thin films can be used in gamma sensors for both optical and electrical applications.

Optical Response of Coated Iron Oxide (s) Nanoparticles Towards Biomedical Applications

We studied the optical properties of coated iron and its oxide (s) nanoparticles as core and silver/gold as shell materials because of their fascinating properties in tissue engineering, cancer therapy, and information storage. The maximum absorption peaks for Fe, FeO, Fe₂O₃ and Fe₃O₄ are found at 421 nm, 1500 nm. 1169 nm and 1100 nm with Ag coating, and 530 nm, 1507 nm, 1115 nm and 1200 nm with Au coating. Furthermore, the larger absorption efficiency has been found at 16 nm Ag/Au shell thickness of all considered core-shell nanostructures and especially absorption efficiency gradually increases for entire considered Au shell thickness. The largest LSPR is found for Fe₂O₃-core with Ag and Au-shell. It is found that the absorption LSPR spectra which are almost fixed for coated iron and varied for coated iron oxides, shows the tunability in the visible and NIR region respectively with increasing shell thickness. The LSPR peaks in visible and NIR region of electromagnetic spectrum opens the door to photonic-magnetic nanodevices, and therapeutic applications.

NIR induced photopolymerization of acrylate-based composite containing upconversion particles as an internal miniaturized UV sources

Abstract Inventing a new light source for overcoming the disadvantages of conventional radiation curing technology is essential. Upconversion particles capable of emitting photon span from ultraviolet to NIR region of electromagnetic spectrum under excitation of NIR laser, could play the role of a light source within the formulation. Different amount of these upconversion particles were introduced to TMPTA monomer in order to survey their curing ability. The curing process was performed under various NIR laser intensities. The monomer to polymer conversion was studied using FT-IR and real-time FT-IR analysis. Increasing the filler content leads to better curing of the composite. Furthermore, the feasibility of curing TMPTMA containing camphorquinone as photoinitiator, by the blue upconversion emission was studied. Besides, the ability of these particles as UV and blue source cooperation in dual curing was observed. Increasing the photo-initiator and upconversion particles concentration resulted in higher double bond conversion. Increasing the laser intensity, by enhancing the upconversion emissions leads to better monomer to polymer conversion. The new source passed the inducing of dual curing process.

Classical trajectories in polar-asymmetric laser fields: Synchronous THz and XUV emission.

The interaction of intense near- and mid-infrared laser pulses with rare gases has produced bursts of radiation with spectral content extending into the extreme ultraviolet and soft x-ray region of electromagnetic spectrum. On the other end of the spectrum, laser-driven gas plasmas has been shown to produce coherent sub-harmonic optical waveforms, covering from terahertz (THz) to mid- and near-infrared frequency spectral band. Both processes can be enhanced via a combination of a driving field and its second harmonic. Despite this striking similarity, only limited experimental and theoretical attempts have been made to address these two regimes simultaneously. Here we present systematic experiments and a unifying picture of these processes, based on our extension of the semi-classical three-step model. Further understanding of the generation and coherent control of time-synchronized transients with photon energies from meV to 1 keV can lead to numerous technological advances and to an intriguing possibilities of ultra-broadband investigations into complex condensed matter systems.

Experimental and theoretical investigation on 2-amino 5-bromopyridinium L-tartrate-A new organic charge-transfer crystal for optoelectronics device applications

A new organic charge transfer (CT) complex of 2-amino 5-bromopyridinium L- tartrate (2A5BPTA) has been synthesized successfully and single crystals were grown by conventional slow evaporation solution technique (SEST). Single crystal X-ray diffraction analysis reveals that 2A5BPTA crystallized in orthorhombic system with noncentro symmetric space group P212121. The various vibrational modes in the crystal were confirmed by FTIR analysis. Optical transmission analysis shows that 2A5BPTA is transparent in the entire visible region of electromagnetic spectrum. Spectral dependence of optical birefringence study was carried out over the wavelength range of 480–620 nm for the crystal thickness of 0.141 mm. Thermal behaviour of the grown crystal has been studied using thermogravimetric and differential thermal analysis. Dielectric studies were carried out for the grown crystal at a different temperature. Photoconductivity study shows that evidence of positive photoconducting nature at room temperature. The NLO characteristics and phase matching ability were explored by powder second harmonic generation studies. Phase matching studies were elucidated for the titled compound. The first order hyperpolarizability investigation was performed using the Gaussian 09 program with B3LYP method.

Effects of temperature on the optical properties of iron oxide (Fe2O3) thin films synthesized by chemical bath deposition

Synthesis of iron oxide (Fe2O3) thin films on glass substrates was carried out by chemical bath deposition technique, with a view to investigate the effects of variation of temperature on the optical properties of the films. Structural characterization of the films obtained by X-ray diffraction (XRD), revealed that they were γ-Fe2O3. The optical property study revealed that the as deposited films had a transmittance of about 75–90% in the VIS-NIR regions of electromagnetic spectrum, but this was slightly reduced to a range of about 70–83% in the same regions when treated with heat. Their band-gap was found to be 2.38eV for the unannealed, while it ranged from 2.55–2.68eV for the annealed films. A variation in other optical properties − refractive index, extinction coefficient etc –, was observed with heat treatment of the films, though not sequential. Their optical properties and band gaps make the films good materials for wide range of applications.

First-principles studies of pure and fluorine substituted alanines

This paper communicates the structural, electronic and optical properties of L-alanine, monofluoro and difluoro substituted alanines using density functional calculations. These compounds exist in orthorhombic crystal structure and the calculated structural parameters such as lattice constants, bond angles and bond lengths are in agreement with the experimental results. L-alanine is an indirect band gap insulator, while its fluorine substituted compounds (monofluoroalanine and difluoroalanine) are direct band gap insulators. The substitution causes reduction in the band gap and hence these optically tailored direct wide band gap materials have enhanced optical properties in the ultraviolet (UV) region of electromagnetic spectrum. Therefore, optical properties like dielectric function, refractive index, reflectivity and energy loss function are also investigated. These compounds have almost isotropic nature in the lower frequency range while at higher energies, they have a significant anisotropic nature.

Structural, electronic and photoluminescence properties of Eu3+-doped CaYAlO4 obtained by using citric acid complexes as precursors

The search for new materials that meet the current technological demands for photonic applications, make the Rare Earth ions embedded in inorganic oxides as excellent candidates for several technological devices. This work presents the synthesis of Eu3+-doped CaYAlO4 using citric acid as ligand to form a complex precursor. The methodology used has big draw due to its easy handling and low cost of the materials. The thermal analysis of viscous solutions was evaluated and the obtained compounds show the formation of a polycrystalline tetragonal phase. Rietveld refinement was used to understand the structural and the cell parameters of the crystalline phase as a function of temperature of heat-treatment. Crystallite size and microstrain were determined and were shown to have a direct relationship with the temperature of the heat-treatment. The band-gap of the CaYAlO4 doped with 1 and 10 mol% of Eu3+ showed values close to 4.30 eV, resulting in their transparency in the visible region between 330 and 750 nm. Besides the intense photoluminescence from Eu3+, a study was conducted to evaluate the possible position of the Eu3+ in the CaYAlO4 as host lattice. Lifetime of the emission decay from Eu3+ excited state 5D0 show that CaYAlO4 is a good host to rare earth ions, once it can avoid clustering of these ions in concentration as high as 10 mol%. The predictions of the sublevels of the 7F1 crystal field level are discussed through the method of equivalent nearest neighbours (MENN). The intensity parameters (Ωλ, λ = 2 and 4) are reproduced with physically reasonable values of average polarizabilities. The set of charge factors used in both calculations are in good agreement with the charge of the europium ion described by the Batista-Longo improved model (BLIM). The quantum efficiencies of the materials were calculated based on Judd-Ofelt theory. Based on the results obtained in this work, the materials have potential use in photonic devices such as lasers and solid state imaging devices in the red region of electromagnetic spectrum.

GPS YER KONTROL NOKTALARI KULLANILARAK LiDAR VERİSİNİN DOĞRULUK ANALİZİ

Gunumuzde, harita uretiminde kullanilan calismalarda, geleneksel olcum tekniklerinden farkli olarak hem daha hizli, hem de dogrulugu daha yuksek yeryuzu verisi elde etme cabalari gun gectikce artmaktadir. Bu calismada, elektromanyetik spektrumun 1.064nm yakin infrared bolgesinde algilama yapan bir Uzaktan Algilama Teknigi olan Hava LiDAR teknolojisinin, yatay ve dusey dogrulugunun RTK/GPS verileri ile (Real Time Kinematik- Global Positioning System) test edilmesi amaclanmistir. Bu kapsamda, Turkiye’nin Dogu Karadeniz bolgesinde yer alan Artvin Ili Borcka ilcesinde 2x2 km2 buyuklugunde bir ormanlik bolge, calisma alani olarak secilmistir. Calismada, RTK/GPS ile elde edilmis Yer Kontrol Noktalari (YKN) ile bu noktalarin karsilik geldigi LiDAR noktalarinin belirlenmesi icin arama capi yontemi gelistirilmis ve ayrica, degisik arazi kategorileri icin karsilastirmali test sonuclari ortaya konulmustur. Calismanin sonucunda, dusey hata miktari (KOHz) normal dagilimda 0.20 m olarak ve %95 guven araliginda dusey dogruluk (dogrulukz) ise 0.39m olarak bulunmustur. Yatay hata (KOHr) normal dagilimda minimum 0.36m, maksimum 1.01m; yatay dogruluk (dogrulukr) ise %95 guven araliginda minimum 0.62m, maksimum 1.75m duzeyinde gerceklesmistir. Bu calismada kullanilan Hava LiDAR verisi icin dusey dogruluk, yatay dogruluga gore yaklasik iki kat daha prezisyonlu olarak gerceklesmistir.