Intense Broadband Research Articles

Structure and low energy vibrations in silver borate glasses with low silver content

Structural changes of (Ag2O)x(B2O3)1-x glasses, over the range between X = 0.0 and X = 0.14, have been monitored by Raman spectroscopy. Low temperature heat capacity measurements have been also performed between 0.4 K and 25 K to investigate along with low frequency Raman scattering the behavior of the low-energy vibrational dynamics. A progressively decreasing intensity of the main band at 808 cm−1 and the appearance of a band at about 775 cm−1 with increasing Ag2O content have been observed and analyzed in detail. The strongly polarized band at 808 cm−1 is ascribed to the breathing vibration of boroxol rings and the decrease of its intensity indicates the reduction of the number of these units in the network. The band at 775 cm−1 is assigned to vibrations of pentaborate units, formed from two boroxol rings linked by a tetrahedral BO4 group. The rate of formation of BO4 groups appears to increase as X/(1-X). Raman investigation has been extended to very low frequencies, where a broad intense band, the Boson peak (BP), dominates the spectrum of all the samples below 100 cm−1. Addition of Ag2O shifts the BP position from 26 cm−1 up to 33 cm−1 and gives rise to a decrease of its intensity up to X = 0.09 and a sudden increase for X = 0.14, which has been explained as due to rattling motion of silver ions whose contribution is added to that of localized vibrations. The formation of tetrahedral BO4 groups stiffens the network and leads to a decrease of the excess heat capacity over the Debye prediction below 20 K, which is not taken into account by the simple hardening of the elastic continuum but seems to follow the reduction of boroxol rings. This result contrasts the observations on borate glasses with high Ag content and emphasizes the crucial role of the network continuity on the vibrational dynamics of a glass.

Characterizing intense broadband THz pulses is necessary for their use in spectroscopic studies

A new study on terahertz waves indicates a more efficient access to frequency regions suitable for spectroscopic applications.

Optical properties of the zinc-tellurite glasses doped with Cr3+ ions

The zinc-tellurite glasses doped with Cr3+ ion have been synthesized using orthotelluric acid, zinc nitrate, and ammonium dichromate as raw materials. According to the yielded results, Cr3+ ions in the spectral range from 0.3 to 2.8 µm demonstrate two intense broad bands with maxima 454 and 650 nm, corresponding to the transitions 4A2g(F) → 4T1g(F) and 4A2g(F) → 4T2g(F). For the studied wavelength range the spectral dependence of the specific coefficient of Cr3+ allows establishing the minimum chromium content for achieving the determined level of optical losses in glasses. The electron paramagnetic resonance spectra of the doped glasses demonstrate that ions Cr3+ are presented both in the isolated ions and in Cr3+−Cr3+ paired in the distorted octahedral site. The optical band gap, Urbach energies, the crystal field and Racah parameters of the prepared glasses have been evaluated.

Near-infrared emissions in host sensitized Ba2YV3O11: RE3+ (RE = Nd, Ho, Yb) down-converting phosphors

Nd3+/Ho3+/Yb3+ single-doped Ba2YV3O11 near infrared (NIR) emitting phosphors were produced using sol-gel route, and their structures were determined by X-ray diffraction (XRD). The down conversion spectra, luminescence lifetime and energy transfer (ET) efficiency of samples have been investigated, which indicate that Ba2YV3O11: Nd3+/Ho3+/Yb3+ phosphors offer intense broad absorption band (250–400 nm) and emit efficient 900–1100 nm NIR emission where the crystal silicon solar cells display the optimal response. The ET processes from [VO4]3- to dopants Nd3+/Ho3+/Yb3+ and possible ET mechanisms were also proposed in detail. Results showed that the Ba2YV3O11: Nd3+/Ho3+/Yb3+ phosphors were potential solar spectral converters for enhancing the silicon solar cell efficiency by absorption enhancement.

Intense stimulated Raman scattering in CO2-filled hollow-core fibers.

We demonstrate experimentally, the generation of an intense broadband comb-like spectrum spontaneously built up through stimulated Raman scattering in a low-pressure CO2-filled hollow-core photonic crystal fiber pumped by a single infrared pump.

Experimental and theoretical studies on isatin-Schiff bases and their copper(II)-complexes: Syntheses, spectroscopy, tautomerism, redox potentials, EPR, PXRD and DFT/TDDFT

Abstract The isatin-Schiff bases 3-(o/p-tolylimino)indolin-2-one (HL1 and HL2) react with the copper(II) acetate or nitrate to give the bis[3-(o/p-tolylimino)indole-2-olato-κ2N,O]copper(II) (1 and 2) via lactam (L)- to enol (E)-tautomerism in solution. IR spectra show solely the L-tautomer at solid state, while both tautomers in solution. 1H NMR results indicate a dynamic tautomerization equilibria between the L- and E-tautomers in solution with varying ratios of ca. 83/17, 60/40 and 54/46 (L/E) within 0.5, 5 and 24 h, respectively. Cyclic voltammograms demonstrate two quasi reversible one electron charge transfer processes for the Cu(II)/Cu(I) and Cu(I)/Cu(0) couples in acetonitrile, respectively. PXRD patterns at 5–50° (2θ) correspond well to the crystalline nature with various degrees of crystallinity for the ligands and complexes. X-band EPR spectrum shows an intense broad band at relatively high field region with isotropic nature. Magnetic moment values (μeff. = 1.56–1.63 μB) indicate paramagnetic nature of the copper(II)-complexes with one unpaired electron in methanol. Optimized structures by DFT show the L-form relatively stable than the E-form by 19.76 kcal/mol, while compounds HL2 and 2 are slightly stable than HL1 and 1 by 0.35 and 0.79 kcal/mol, respectively. Electronic spectra by TDDFT strongly support the experimental results in methanol.

Broadband Near-IR photoluminescence of bismuth-doped pollucite-related phase CsGaGe2O6

Polycrystalline samples of bismuth-doped CsGaGe2O6 with pollucite-related structure were prepared by crystallization from the melt. Intense broadband near-IR photoluminescence was observed in this phase. The photoluminescence emission and excitation spectra are characteristic for Bi+ monocation. Structural disorder in the framework of pollucite-related phase leads to the inhomogeneous broadening of photoluminescence emission spectrum. The influence of melt composition on the stabilization of subvalent Bi+ monocation was discussed in the terms of oxoacidity concept.

Value-addition of water hyacinth and para grass through pyrolysis and hydrothermal liquefaction

Hydrothermal liquefaction (HTL) and pyrolysis (Py) of Loktak lake biomass mixture of water hyacinth (WH) and para grass (PG) were carried out at 260–300 °C and 300–500 °C to compare the products yield and chemical characteristics of the products. In case of HTL, the maximum bio-oil yield was obtained 13.34 wt.% at 280 °C while for Py, the maximum bio-oil yield was observed 38.8 wt.% at 350 °C. The obtained bio-oils and bio-chars were analyzed using GC–MS, FT-IR, NMR, TGA, TOC, and SEM. GC–MS analysis of the bio-oils were showed that the HTL bio-oil majorly contains of nitrogen containing compounds whereas the Py bio-oil contains majority of phenolic compounds. Other compounds like ketones, alcohols, acids were also observed in bio-oil. Higher intensity broad band at 3300–3500 cm−1 was observed in the Py bio-oil compared to HTL bio-oil. TGA and proximate analysis of bio-char revealed the higher devolatilization occured during the HTL compared to Py process. The surface morphology of the HTL bio-char was found to be rough and fragmented as compared to the pyrolysis bio-char, clearly showing the biomass macromolecules breakdown differently in HTL and Py process.

Biohydrolysis of Banana and Plantain Peels for the Production of Biofuel

This study was carried out to assess the potentials of banana and plantain peel as feedstock for biofuel production. Fungi were isolated from spoiled banana, burkutu and spoiled bread using the standard microbiological method. The concentration of reducing sugar of the peels were measured using DNS calorimetry method and biofuel were measured using chromium (VI) reagent by Ultraviolet-Visible Spectrophotometer. Aspergillus niger, Saccharomyces cerevisiae and Mucor racemusus were isolated. A reducing sugar concentration of 59.12 mg/g and 56.62 mg/g was observed for the banana and plantain peels. The highest concentration was found to be 0.35 mg/L for banana peels and 0.10 mg/L for plantain. The IR characterization of the banana and plantain sample revealed an intense strong broad band of alcohol O-H and alkane C-H stretching. The GC-MS result revealed the presence of benzaldehyde in all the biomass while 2,3-butanediol was only detected in the plantain peels biomass. This study showed the potential of banana and plantain peels biomass for biofuel production.

Relativistic air-plasma far-infrared radiation effects by ultrashort laser pulses in air

Interactions of ultrashort laser pulses with gases have a wide variety of applications including lighting control, electromagnetic radiation and remote sensing. Considering the radiation effects, the ionization process, plasma formation and the current produced due to the formed plasmas, are the important fundamental processes. Here, a 2D relativistic fluid model is presented in which the interaction of an ultrashort laser pulse with air, leading to the electromagnetic pulse generation, is investigated. As the model is relativistic, it is appropriate for the investigation of the air-plasma radiation effects at high intensities. The results show that the intense laser-air interaction is suitable for the intense broadband far-infrared pulse generation due to the fact that the wave amplitude increases with the laser intensity. Moreover, for the laser intensities above 1020 W/m2, the laser pulse magnetic field gives rise to a strong axial electron current and a consequent axial wave component, which has to be accounted for in the proposed physical models. In addition, the Fourier transform analysis reveals that the radiated pulse is broadband and its frequency spectrum is not affected by the laser intensity.

Emission properties of Nd3+:Y2Si2O7 nanocrystals under high excitation power density

In present work the influence of high excitation power density of laser diode on emission properties of Y2Si2O7:Nd3+ nanocrystals is reported. It was found that if a characteristic power threshold is exceeded intense broadband was observed in visible and infrared regions. It increased with a simultaneous decrease of f-f transitions. In particular, the influence of excitation power density and concentration of Nd3+ ions were investigated. The intensity of white emission was characterized by exponential dependence on excitation power density and threshold behavior. Moreover, it increased with the concentration of Nd3+ ions demonstrating exponential dependence due to the cooperative interaction between Nd3+ ions. The photocurrent accompanying the laser induced broadband white emission was measured. It increased exponentially with excitation power and Nd3+ concentration.

Weak thermal quenching of the luminescence in Y2.94-xLuxAl4GaO12: 0.06Ce3+ green phosphor for white light-emitting diodes

A series of Y2.94-xLuxAl4GaO12: 0.06Ce3+ phosphors were prepared by the conventional solid-state reaction method. It was confirmed that the phosphors exhibit cubic garnet crystal structures by XRD and Rietveld refinements. The phosphors show an intense broad emission band from 475 nm to 650 nm, which attributed to the 5d→4f transitions of the Ce3+ ions under the excitation of 450 nm. Simultaneously, obvious blue shift is observed from 518 nm to 497 nm with increasing Lu3+ concentrations from 0 to 2.94. With the increase of Lu3+ concentrations the emission intensity increases and reaches to the maximum for x = 2.5. By optimizing Lu3+ concentration, the quantum efficiency up to 89.8% is obtained. The emission intensity at 453 K is up to 92% of that at room-temperature indicating a weak thermal quenching and a superior thermal stability. These results indicate that the phosphor can be used in blue LED-Chip based white LEDs in the future.

Effect of up-conversion luminescence in Er3+ doped phosphate glasses for developing Erbium-Doped Fibre Amplifiers (EDFA) and G-LED's

The (NPbPEr) glasses of the composition (20-x) Na2SO4–20PbO–60P2O5-xEr2O3 (x = 0.1, 0.3, 0.5, 0.7, 1.0 mol %) are synthesized by melt quenching process. The basic characterization studies like XRD and EDS have confirmed amorphous nature and contents of the samples. The spectroscopic studies viz., optical absorption, photoluminescence (PL) and decay profiles were carried out. The PL spectra exhibited an intense sharp green emission peak at 544 nm due to 4S3/2 → 4I15/2 transition of Er3+ ions both in down-conversion (DC, λexc = 377 nm) and up-conversion (UC, λexc = 977 nm) PL spectra. The spectra also exhibited a broad intense NIR band at 1532 nm ascribed to 4I13/2→4I15/2 transition of Er3+ ions at λexc = 977 nm. The analysis of the spectra indicated 0.5 mol% of Er2O3 is the optimal concentration for achieving maximal PL output both in the green and in NIR regions. The CIE color coordinates and the corresponding CCT (K) values were estimated from both UC and DC emission spectra. Overall analysis of the results suggested that the investigated glasses are potential candidates for getting intense green light emission and are quite suitable as optical fibre amplifiers in the green and NIR (around 1.5 μm) regions.

Effect of novel Nd3+ doping on physical properties of nebulizer spray pyrolysis fabricated ZnS thin films for optoelectronic technology

Neodymium doped zinc sulphide (Nd: ZnS) thin films were coated on glass substrates at 450 °C through low cost nebulizer spray pyrolysis (NSP) method. Structure, morphology, opto-electrical characteristics of Nd doped ZnS films with various Nd doping concentrations (0%, 1, %, 3% and 5%) were studied. X-ray diffraction patterns revealed that all coated films were polycrystalline hexagonal structure with (102) as a preferential direction. SEM images showed smooth and uniform spherical grains without any cracks and pinholes. Topological view by AFM described the increasing of roughness of the film through doping concentration. EDAX and Elemental mapping images confirmed the presence of Zn, S and Nd without any other impurities. Raman spectra reveals that E1(LO), 2TO, 2LO and 3LO emission modes with corresponding to the wave number. PL spectra showed high intense visible and broad UV emission band at 463 nm and 397 nm, respectively. Thickness of the films increased with Nd doping concentration reflecting the reduction of transparency of the films from 86% to 78% for 0% and 5% of Nd. UV–Vis Spectrum was used to study the energy gap (Eg), dielectric constant(ε), refractive index(n), and extinction coefficient (k) of the prepared films. Four-point probe method was used to calculate the activation energy of Nd: ZnS thin films from the graph drawn between ln (ρ) and (1/T).

Impacts of broadband sound on silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp hearing thresholds determined using auditory evoked potential audiometry.

Invasive silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp, collectively referred to as bigheaded carps, threaten aquatic ecosystems of the Upper Midwestern USA. Due to the extensive ecological impacts associated with these species, prevention of their further range expansion is the aim for fisheries management. Recent behavioral studies indicate bigheaded carps are deterred by acoustic barriers and exhibit negative phonotaxis in response to anthropogenic sound sources (≥ 150dB re 1μPa). However, the impact of long-term exposure to these sounds on the hearing capabilities of bigheaded carps has not been well documented. In this study, the auditory evoked potential (AEP) technique was used to determine auditory thresholds among bigheaded carps before and after exposure to high intensity (155.7 ± 4.7dB re 1μPa SPLrms; - 8.0 ± 4.7dB re 1ms-2 PALrms; mean ± SD) broadband sound. Fish were exposed to sound for 30min or 24h and AEP measurements were taken at three time points: immediately after exposure, 48h, or 96h later. Results indicate that silver and bighead carp experience temporary threshold shifts (TTSs) in frequency detection following sound exposure with the magnitude and length of TTS correlated with exposure duration. The findings from this study will be used to increase the long-term efficacy of acoustical deterrent measures aimed at preventing further range expansion of bigheaded carps.

Broadband Intensity Tomography: Spectral Tagging of the Cosmic UV Background

Abstract Cosmic photons can be efficiently collected by broadband intensity mapping but information on their emission redshift and frequency is largely lost. We introduce a technique to statistically recover these otherwise collapsed dimensions by exploiting information in spatial fluctuations and apply it to the Galaxy Evolution Explorer (GALEX) All Sky and Medium Imaging Surveys. By spatially cross-correlating photons in the GALEX far-UV (1500 Å) and near-UV (2300 Å) bands with a million spectroscopic objects in the Sloan Digital Sky Survey as a function of redshift, we robustly detect the redshift-dependent intensity of the UV background (UVB) modulated by its clustering bias up to z ∼ 2. These measurements clearly reveal the imprints of UVB spectral features redshifting through the filters. Using a simple parameterization, we simultaneously fit a UVB emissivity and clustering bias factor to these observations and constrain the main spectral features of the UVB spectrum: (i) the Lyman break, (ii) the non-ionizing UV continuum, which agrees with the Haardt & Madau model but does not rely on any assumption regarding the nature of the sources, and (iii) the Lyα emission, the luminosity density of which is consistent with estimates of the combined galaxy and active galactic nucleus contributions at z ∼ 1. Because the technique probes the total background including low surface brightness emission, we place constraints on the amount of UV light originating from the diffuse intergalactic medium (IGM). Finally, the clustering bias of UV photons is found to be chromatic and evolving. Our frequency- and redshift-dependent UVB measurement delivers a summary statistic of the universe’s net radiation output from stars, black holes, and the IGM combined.

Piston sensing of sparse aperture systems with a single broadband image via deep learning.

The pistons of sparse aperture systems need to be controlled within a fraction of a wavelength for the system's optimal imaging performance. In this paper, we demonstrate that deep learning is capable of performing piston sensing with a single wide-band image after appropriate training. Taking the sensing issue as a fitting task, the deep learning-based method utilizes a deep convolutional neural network to learn complex input-output mapping relations between the broadband intensity distributions and corresponding piston values. Given a trained network and one broadband focal intensity image as the input, the piston can be obtained directly and the capture range achieving the coherence length of the broadband light is available. Simulations and experiments demonstrate the validity of the proposed method. Using only in-focused broadband images as the inputs without defocus division and wavelength dispersion, obviously relaxes the optics complexity. In view of the efficiency and superiority, it's expected that the method proposed in this paper may be widely applied in multi-aperture imaging.

A PL and PLE Study of High Cu Content Cu2ZnSnSe4 Films on Mo/Glass and Solar Cells

Cu2ZnSnSe4 (CZTSe) is amongst leading candidates for the absorber layer in sustainable solar cells. We examine CZTSe thin films with [Cu]/[Zn + Sn] of 0.99 and [Zn]/[Sn] of 1.07, deposited on Mo/glass substrates, and solar cells fabricated from these films. The bandgap (Eg) of the as deposited films and solar cells was examined by photoluminescence excitation (PLE) whereas the temperature and excitation intensity dependence of photoluminescence (PL) spectra was used to examine the nature of radiative recombination. The 6 K PL spectra of CZTSe/Mo exhibit an intense broad and asymmetrical band P1 at 0.822 eV and a lower intensity band P2 at 0.93 eV. The shape of this band, high rates of blue shift with excitation intensity rise ( j-shift) j(P1) = 14 meV and j(P2) = 8 meV per decade, and red shifts of both bands with increasing temperature suggest that both bands are associated with valence band tails due to potential fluctuations caused by high populations of charged defects. The mean depth of such fluctuation γ of 24 meV was estimated from the low energy side of P1. Device processing increased Eg, blue shifted P1, decreased its width, j-shift and the mean depth of potential fluctuations. These can be due to the annealing and/or can partly be related to KCN etching and the chemical effect of Cd, from CdS replacing copper at the CdS–CZTSe interface layer. Processing induced a new broad band P3 at 1.3 eV (quenching with Ea = 200 meV). We attributed P3 to defects in the CdS layer.

A facilely one pot low temperature synthesis of novel Pt doped PbS nanopowders and their characterizations for optoelectronic applications

Different concentrations of Pt doped PbS nanostructures synthesis has been attained facilely by chemical route. X-ray diffraction (XRD) and FT-Raman spectroscopy analyses confirms the structure. After close inspection and indexing of diffraction peaks, the absence of additional peak owing to any contamination or free Pt in final products was confirmed. XRD data was further used to evaluate the lattice constants, crystallite size, density and strain to see the effect of Pt on these. Calculated lattice parameters confirm the single cubic phase, which was in correlation with vibrational modes analysis. The crystallite size was calculated in range from 9 to 11 nm. For further confirmation of Pt doping and its homogeneity in final product the EDX/SEM mapping was carried out and approved the homogeneous presence of Pt in PbS. SEM study revealed that the morphology is changing from nanoparticles (NPs) to nanosheets (NSs). Diffused reflectance spectra (DRS) were measured for powdered samples and energy gap was estimated up to 1.32 eV. Photoluminescence spectra was recorded and shows an intense green and broad red emission bands at 518 and 700 nm, correspondingly. The values of dielectric constant are found in range of 18–28. Total ac electrical conductivity is rising with applied frequency. The energy gap value suggest the application of synthesized Pt:PbS NPs and NSs in solar cell.

Some insights into the mechanism of photoluminescence of As-S-based films synthesized by PECVD

Chalcogenide arsenic sulphide thin films were obtained by reacting arsenic and sulfur vapors in a low-temperature plasma discharge. Photoluminescence (PL) of As-S films with compositions As34S66 and As53S47 is studied in detail. An increase in the arsenic concentration leads to the emergence of a crystalline phase in the As53S47 films. In addition, these films exhibit an intense broad PL band with a maximum at 2.2 eV upon a continuous 473 nm laser excitation. The interplay between composition, structure and optical properties is revealed. By coupling of PL, Raman spectroscopy and absorption data, possible mechanisms of radiative recombination in the context of the glass structure formation in the plasma discharge are discussed.