Optical Investigations Research Articles

Nanoscopic structural and optical investigations on blue InGaN single quantum wells serving as layers beneath efficient red active layers

In state-of-the-art red InGaN light-emitting diodes (LEDs), an InGaN-based blue single quantum well (SQW) is used as an underlying layer to improve the red emission efficiency. However, the role of blue SQW is not fully understood. This study investigates the structural and optical properties of blue InGaN SQW by atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy under scanning near-field optical microscopy (SNOM). The AFM images reveal deep and shallow V-pits, corresponding to screw and mixed threading dislocations (TDs). The SNOM-PL intensity image illustrates that all the V-pits correspond to dark spots. We also observe dark spots not associated with the V-pits; given the correspondence between the dark spot density and the edge TD density estimated via x-ray diffraction measurement, these dark spots likely originate from edge TDs. Unlike previous studies, we find that TDs act as nonradiative recombination centers (NRCs) in recent blue SQW, most likely because of the reduction of point defects by InGaN/GaN superlattices. Edge, screw, and mixed TDs have nearly the same impact on the integrated PL intensity of the blue InGaN SQW. Given the correlation of dark emission positions between the blue and red emissions in hybrid red InGaN LEDs in our prior study, all the TDs should function as NRCs in the red emission. The comparable dark spot density between the blue and red SQW suggests that blue SQW suppresses the generation of NRCs in red SQW.

NH2-MIL-125(Ti)/TiO2 heterojunction with non-disturbed dual reactive centers for synchronous photocatalytic removal of Cr(VI) and organic dyes.

Chromium (VI) (Cr(VI)) generally coexists with organic dyes in industrial effluents, posing a formidable challenge in water purification. Herein, NH2-MIL-125(Ti)/TiO2 Z-scheme heterojunction with intimate interfacial contact was synthesized for synchronous removal of pollutant in coexisting Cr(VI)/dyes system under simulated solar irradiation. Structural and optical investigations indicated that a well-defined interface was formed by establishing a Ti-N-C bond, facilitating the spatial separation of the photoexcited carriers of the Z-scheme heterojunction. The optimum NH2-MIL-125(Ti)/TiO2 nanocomposites show superior performance in photocatalytic removal of the pollutants in the Cr(VI) (5mg/L, 97.2%)/MB (40mg/L, 100%) coexistence systems within 120min, which is comparable to that in the single system. The electron spin resonance (ESR) tests, radicals scavenging experiments, and density functional theory (DFT) cannulations unveiled that TiO2 could serve as oxidation centers to generate hydroxyl radicals (•OH) for MB oxidation, while the NH2-MIL-125(Ti) with exposed Ti nodes could act as reduction centers to effectively adsorb Cr2O72- and inject photo-generated electrons (e-) to accomplish the in-site photoreduction of Cr(VI) into Cr(III) under illumination. Particularly, owing to the spatial separation and non-disturbed dual reactive centers, the reduction and oxidation processes could be well accommodated, which could allow MB and Cr(VI) to be removed synchronously. This work demonstrated the great potential of applying duel reactive centers to eliminate multipollutant simultaneously in the actual scenarios for wastewater treatment.

Structural, optical, and dielectric investigations of sodium-modified lead-bismuth borate glasses

Structural, optical, and dielectric investigations of sodium-modified lead-bismuth borate glasses

An optical investigation of the effects of diesel injection pressure and intake air temperature in an ammonia-diesel dual-fuel engine under low-load conditions

An optical investigation of the effects of diesel injection pressure and intake air temperature in an ammonia-diesel dual-fuel engine under low-load conditions

Optical investigation of supernova remnant G206.7+5.9

Abstract The shell-type supernova remnant (SNR) G206.7+5.9 was recently discovered in the radio band with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The remnant spans about 3.○5 in diameter and exhibits bilateral shells. In this work, we present optical spectra of G206.7+5.9 with the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST), and narrow-band (Hα and [S ii]) images with the 1-m T100 telescope. The filamentary structure seen in Hα image shows a clear correlation with the radio emission. We use optical line ratios to determine the physical parameters of G206.7+5.9. The LAMOST spectra reveal large ratios of [S ii]/Hα ∼ (0.61−1.78) and [N ii]/Hα ∼ (0.63−1.92) consistent with that expected for a shock-heated SNR. The emission lines [O i] λ6300, λ6363 detected in the spectra also support the presence of shocks. Electron density (ne) measurements based on the [S ii] λ6716/λ6731 ratio suggest densities between 117 and 597 cm−3. We estimate the pre-shock cloud density (nc) to be approximately 2.6−13.3 cm−3. We also investigate the archival H i data and have newly identified an expanding gas motion of the H i, whose velocity span is approximately 10 km s−1. We conclude that G206.7+5.9 is an SNR exhibiting properties remarkably similar to those seen in Galactic SNRs.

Effect of Ti Doping on the Structural, Electronic, Optical and Thermoelectric Properties of ZrO2: A Systematic DFT Approach

AbstractIn this work, the density functional theory (DFT) calculations in wien2k code to investigate the effect of (Titanium) Ti doping (25% and 50%) in ZrO2 is utilized. The negative values of the Ef, i.e., −2.14, −3.42 and −2.31 as well as energy versus volume curves show the stability of pure, 25% and 50% doped ZrO2. From band structure and density of states results it is confirmed that upon doping Ti, the band gap of ZrO2 become direct from indirect and reduces from 3.10 eV to 1.26(25% doped)/1.16(50% doped). The optical investigations reveal that incorporation of Ti improved the optical properties significantly, which show the significance of these materials for optoelectronic device applications. The thermoelectric properties are investigated using the Boltzmann transport theory. The Seebeck coefficient, electronic conductivity, thermal conductivity, power factor and figure of merit is calculated. The obtained results show that the under study compounds are best candidates for different thermoelectric applications.

SN 2023xwi: Forbidden line emission in the peak spectrum of a Ca-strong transient

Abstract We present an extensive optical photometric and spectroscopic investigation into the calcium-rich supernova (SN) – SN2023xwi. Observations from a variety of ground-based telescopes follow the SN from 8 days pre-peak brightness to 87 days post-peak, covering both early-time (photospheric) and late-time (nebular) phases of the supernova. Objects of this class are characterised by nebular spectra that are dominated by [Ca II] λλ 7291, 7324 emission. SN 2023xwi displays a unique peculiarity in that its forbidden [Ca II] feature is visible in its peak photospheric spectrum – far earlier than expected in current models. This is one of the strongest and earliest detections of this feature in Ca-rich SNe in photospheric-phase spectra. We investigate the velocity evolution of this spectral feature and show that it cannot be easily explained by conventional progenitor systems. From our observations, we propose a SN progenitor embedded in an environment polluted by a recurrent He-nova AM CVn system.

Polarized UV–Visible Photoluminescence from Bulk β‐Ga2O3 Crystals

Herein, a study of photoluminescence (PL) of bulk β‐Ga2O3 crystals measured at different crystallographic directions is presented. The bulk β‐Ga2O3 crystals are grown using the optical floating zone method and cut to prepare three basic planes for optical investigations. The Ga2O3 emits PL from red (1.7 eV) to near UV (3.5 eV). The maximum is at about 3 eV. It is shown that the excitation of Ga2O3 depends on polarization: the lowest excitation energy 4.7 eV is observed for polarization along the b axis. The PL emission is clearly polarized, which can be used to build diodes emitting polarized light: polarized light‐emitting diodes. For example, the main emission from the (100) plane is polarized along [001] direction. Analysis of polarization and dynamics of PL shows that the main emission band is composed of a few spectrally overlapping luminescence bands. The bands are resolved thanks to different polarization and significantly different dynamics. The violet PL at about 3.0 eV has a lifetime τ = 0.6 μs and the blue PL at about 2.8 eV has τ of about 600 μs. Such long lifetimes are characteristic of deep centers, for example, the oxygen vacancy VO or the VGa–Gai–VGa defect.

An efficient phase matching second harmonic generation of 2-amino-4-methylpyridinium quinoline-2-carboxylate (C16H15N3O2) organic single crystal: structural, optical, thermal, and computational investigations

An efficient phase matching second harmonic generation of 2-amino-4-methylpyridinium quinoline-2-carboxylate (C16H15N3O2) organic single crystal: structural, optical, thermal, and computational investigations

Structural and optical investigations of lithium-modified lead bismuth borate glasses

Structural and optical investigations of lithium-modified lead bismuth borate glasses

Fast determination of terahertz polarization azimuth angle based on the core-anti-resonant effect

The azimuth angle of linearly polarized light plays a crucial role in optical mechanism investigations and various applications. However, in the terahertz (THz) band, traditional detection methods suffer from low efficiency or require complex apparatus. In this work, based on the core-anti-resonant reflection (CARR) principle, we propose a polarization-sensitive CARR cavity, namely, a simple 3D-printed tube with an Archimedean spiral structure of the cross section, which links the input linear polarization azimuth angle to the output resonant frequencies. In this way, the spatial polarization angle can be rapidly resolved via the Fourier-transformed THz spectrum from the detected single THz temporal pulse. Therefore, the experimental system configuration is simplified, and more importantly, the detection efficiency has been significantly enhanced.

Electronic, structural and nonlinear optical investigation of manganese carbonyl complexes of isatin derivatives by DFT.

Isatin-Schiff bases have wide applications in chemistry. The π conjugated electronic system and heterocylic structure of these materials make them valuable for use as photosensitized materials. The delocalization of π-electrons throughout the structure causes the UV-vis absorption spectra to shift to longer wavelengths. In this study, the isatin manganese carbonyl complex shifted the UV-vis absorption wavelength to a longer wavelength (vis. 400-700nm) compared with our previous studies. The isatin derivatives (ISE (3[4-ethyl(phenyl)imino][indoline-2-one]), ISB (3[4-butly(phenyl)imino][indoline-2-one])) and their Mn carbonyl complexes MnISE ((ISE)Mn(CO)3), and, MnISB ((ISB)Mn(CO)3) were investigated via density functional theory (DFT) in different solvent media. The most stable complexes were found in medium polarity THF. The calculated HOMO-LUMO energy gap shows that the charge transfer occurs within the molecule. The HOMO-LUMO energy gap was increased with increasing solvent polarity for all investigated compounds. The smaller energy gap indicates that charge transfer occurs within the Mn(II) complex, in contrast to ISE and ISB, which exhibit larger energy gaps. As a result, the maximum absorption of Mn complexes shifts to the visible region. MnISB has the smallest HOMO-LUMO energy gap in THF. Additionally, the global reactivity parameters indicated that the MnISE complex has the highest electrophilicity index. DFT calculations have also been performed to investigate polarizability and first-order hyperpolarizability of these compounds. In water, the ISE had higher NLO values than the other structures did. These results indicate that all the studied molecules in different solvents could be good candidates for use in photosensitized and nonlinear optical materials. Geometries were determined at the DFT level via the LANL2DZ basis set for Mn and cc-PVTZ for other atoms in the molecules with the B3LYP functional. The UV-vis absorption spectra and HOMO-LUMO energies of ISE, ISB, and their Mn complexes were calculated by Time-dependent DFT (TDDFT) with CAM-B3LYP using the same basis sets. The UV-vis absorption spectra of ISE were also measured in acetonitrile and compared with the calculated spectra, which were consistent with the experimental results. All calculations were repeated in different solvents with the polarizable continuum model (PCM).

Morphological and optical investigation of Ce doped La2O3 nanoparticles for photocatalytic applications

Morphological and optical investigation of Ce doped La2O3 nanoparticles for photocatalytic applications

Carbazole, Fluorene, and Silafluorene Bearing Non-Fullerene Acceptors: Synthesis, Characterization, and Performance in Organic Photovoltaic Devices.

Due to their tunable energy levels, ability for intense light absorption, stability and ease of purification, non-fullerene acceptors (NFAs) have significantly contributed to the progress of organic photovoltaics (OPVs). Herein, a series of newly designed and synthesized NFAs specifically tailored are presented for OPV applications. A new class of NFAs possessing carbazole, fluorene, silafluorene derivatives, and benzothiadiazoles are synthesized. The electrochemical and optical investigations are conducted thoroughly. The utilization of these new materials with commercial donor polymers P3HT and PTB7-Th in OPVs shows their potential applications for future studies. The optimal performance is achieved with an inverted structured OPV device, which demonstrates a power conversion efficiency (PCE) of 3.77%, an open-circuit voltage (VOC) of 1.06V, a short-circuit current (JSC) of 9.66mAcm- 2, and a fill factor (FF) of 37.08%.

Structural, Morphological and Optical Investigations of Pure and Iron Doped Manganese Sulfide Thin Film by Chemical Bath Deposition

Thin films of pure and iron doped MnS, have been deposited on glass substrates using a straightforward and cost-effective technique named Chemical Bath Deposition (CBD). The temperature of the heating water bath was maintained at 90°C for three hours of deposition. Deposition is done by varying the doping concentration of Fe from 0 to 10%. Manganese chloride, iron chloride tetrahydrate, urea, and thioacetamide were the precursors employed in this work. The X-ray diffraction method was used to ascertain the thin film's structural properties. Using the Scherrer formula, the average crystallite size for an undoped MnS thin film was observed to be 30.28 nm and is decreased to 24.02 nm for 4% of Fe doping. For an undoped MnS thin film, the values of dislocation density and material strain were 1.09× 10−3()−2 and 3.418× 10−3, respectively. These values were increased to 1.73× 10−3()−2 and 4.65× 10−3, respectively due to decrement in the crystallite size. Grain size and morphology were examined using Scanning Electron Microscopy (SEM). Micrographs of samples were obtained at different magnifications and their values were noted as 0.9 μm for pure and 4.69 μm for 4% Fe doped thin films. Optical properties were determined using DRS method. The energy band gap was found as 2.21 eV for pure samples and it was decreased to 2.14, 2.09, 1.98, 1.96 and 1.93 eV for 2, 4, 6, 8 and 10% iron doping, respectively. Solar cells, solar selective coatings, sensors, optical mass memory, and anti-reflection coatings have all made substantial use of MnS thin films.

Structural, electronic, vibrational, optical and thermoelectric properties of 1T-Na2O monolayer via MD and DFT study

Abstract Density Functional Theory (DFT) was implemented to determine the physical properties of the 1T-Na2O monolayer with the aid of WIEN2k software. To determine the electronic property exchange correlation such as GGA and hybrid functionals were implemented. The electronic property studies unveiled the 1T-Na2O monolayer as a direct bandgap semiconductor that has band gap values of 1.68 eV and 2.75 eV with GGA and hybrid correlation functionals. The dynamical stability of the 1T-Na2O monolayer was established by harnessing Phonon dispersion analysis, while the thermal stability was established by harnessing the Ab-initio Molecular Dynamics (AIMD). The optical properties investigation revealed that the 1T-Na2O monolayer shows an excellent absorption coefficient in the UV region and has a potential application in optoelectronic applications. The 1T-Na2O monolayer shows promise for waste heat recovery systems due to its thermoelectric properties, with a figure of merit of 0.82 at 400 K. The effective masses of electrons and holes (charge carriers) are determined. The relative ratio was estimated to determine the recombination rate of charge carriers and was found to be limited.

Optical Investigations of Nano‐LEDs Based on Submicron‐Sized III‐Nitride Platelets

A study of submicron‐sized InGaN containing a single quantum well, intended for use as nano‐light‐emitting diodes in high‐resolution display based on direct emission, is presented. Herein, the structures are grown by a bottom‐up method from holes in a masked GaN/sapphire substrate and are intended for red emission. Many of the platelets show dark lines in cathodoluminescence images, previously identified as stacking mismatch boundaries. These introduce local shifts in the reduced emission, perhaps related to local strain. However, the total emission position stays unaffected, just reduced in intensity. Due to an unintended variation in the size of the c‐facet, there is a gradient in the indium content which, in turn, leads to a significant shift in the peak position of the quantum well emission. With increasing probe current there is a slight blueshift, likely a result of the quantum confined Stark effect.

Linear and Nonlinear Optical Characteristics of Basic Fuchsin-Doped Polyvinyl Alcohol Films for Flexible Optoelectronics

Abstract Polyvinyl alcohol (PVA) containing different levels of basic fuchsine (BF) was prepared using the solution casting method. Characterization via Fourier-transform infrared spectroscopy detailed changes in functional groups within the PVA/BF composites, indicates the hydrogen bonding between OH group of PVA and BF molecules. Optical investigations spanning the 190-2500 nm range demonstrated UV blocking properties in prepared PVA/BF composites (fromn 2.05 to 2.56 eV and from 4.08 to 6.32 eV). Moreover, the studies on optical band gap indicated a decrease with increased BF concentrations, reflecting altered electronic transitions within the prepared composites. The study also employed the single oscillator model provided by Wemple-DiDomenico to elucidate refractive index variations. After incorporating BF dye into the PVA polymer, the values of the dielectric constant as the frequency approaches infinity (ε∞), the dielectric constant of lattice (εL), dispersion energy (Ed), and oscillator energy (Eo) in PVA/BF composite samples showed an increase. Moreover, the nonlinear optical properties, including optical susceptibility and nonlinear refractive index were investigated and discussed. These findings underscore the versatility of PVA doped with BF for various applications including optical filters, and solar cell devices.

New imidazole sensors synthesized for copper (II) detection in aqueous solutions

Water security, safety, availability and sustainability of water supply are increasingly problematic and difficult across the planet. Safe and rapid methods have been developed to purify water from cationic pollutants. New imidazole-derived fluorescent sensors, 2-(4,5-diphenyl-1-(p-tolyl)-1H-imidazol-2-yl) phenol (TS) and 2-(1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazol-2-yl) phenol (AS), have been synthesized and characterized, and their possibility as fluorescence sensors for copper (II) has been examined. In CH3CN/H2O (90 v/v), the TS and AS revealed a noticeable an electronic band at 320.00 nm and fluorescence band at 460.90 nm. The ratio metric alterations in the absorption and fluorescence spectra of TS and AS due to the dative covalent bond between them and the copper (II) were shown by the findings of copper (II) titration. The sensing mechanism was validated by optical investigations and FT-IR spectra. In mixed solvent solutions, the selectivity of TS and AS to copper (II) as fluorescent sensors has been demonstrated, with sensitivity as low as 0.09 and 0.28 µM, significantly less than the limit permitted via the US EPA for drinking water (2.00 µM). The identification limits of TS and AS were assessed to be 0.05 and 0.50 µM, respectively, using the spectrophotometric procedure. Stoichiometry binding between TS and AS with copper (II) was found to be 2:1 (tetrahedral structure) as indicated by Job's method.

Combined Raman spectroscopy and electrical transport measurements in ultra-high vacuum down to 3.7 K

An instrument for the simultaneous characterization of thin films by Raman spectroscopy and electronic transport down to 3.7 K has been designed and built. This setup allows for the in situ preparation of air-sensitive samples, their spectroscopic characterization by Raman spectroscopy with different laser lines and five-probe electronic transport measurements using sample plates with prefabricated contacts. The lowest temperatures that can be achieved on the sample are directly proven by measuring the superconducting transition of a niobium film. The temperature-dependent Raman shift and narrowing of the silicon F2g Raman line are shown. This experimental system is specially designed for in situ functionalization and optical spectroscopic and electron transport investigation of thin films. It allows for easy on-the-fly change of samples without the need to warm up the cryomanipulator.