Optical Emission Bands Research Articles

Sulfur deficiency mediated visible emission of ZnS QDs by magnesium dopant and their application in waste water treatment

The photocatalyst with antimicrobial activity serves as a better candidate material for wastewater treatment, as wastewater contains microbes, hazardous dyes, and heavy metals. Hence, the present study extensively examines the photocatalytic and antibacterial activities against two waterborne bacterial strains, namely Salmonella typhi and Escherichia coli. Pure and Mg-doped ZnS (Mg:ZnS) quantum dots (QDs) were synthesized using a low-cost and simple co-precipitation method. The QDs' structural, surface morphology, chemical purity, and optical characteristics were analyzed through XRD, SEM, EDAX, TEM, UV–visible, and photoluminescence spectra. The incorporation of Mg dopants did not introduce significant alterations to the cubic blende structure of ZnS, nor did it induce substantial changes in the structural parameters. However, the QDs exhibited a slight sulfur deficiency, which was further increased by the presence of Mg dopant. The Mg dopant, due to its dominant compositional effect, reduced the band gap. Several optical emission bands were observed in the UV, violet, blue, and green regions, corresponding to NBE emission, sulfur-related defects, and Zn-related defects. Initially, Mg doping enhanced visible emission related to defects, while NBE emission was suppressed by the Mg dopant. However, increasing the concentration of the Mg dopant led to a slight increase in NBE emission. The Mg dopant enhanced the photocatalytic activity of the QDs, and a strong correlation was found between photocatalytic activity and NBE emission. The presence of the Mg dopant led to an increased rate of ROS-based decolorization by reducing the electron-hole recombination rate.

Quantitative analysis of trace N2, Ar in O2 using glow discharge optical emission spectroscopy.

A trace level of N2 and Ar gases in O2 ambience were quantitatively analyzed for the first time by glow discharge optical emission spectroscopy. Microplasma was generated in a compact gas cell by a metal (Au) electrode pair of 1mm diameter and ∼1mm separation with the driving voltage of ∼0.9kV and the current of ∼5 mA in ∼60 Torr. 358 and 813nm optical emission bands were used for N2 and Ar detection, respectively. A spectroscopy fiber bundle having a circular input cross section of ∼700 µm in diameter and an output of 100 µm in width and 3mm in height was employed to promote the signal collection efficiency while preserving high spectral resolution. As a result, the detection sensitivities <1 ppm (3 - σ) were attained for both N2 and Ar within 10s. The detection accuracy was also promoted by correcting the N2 and Ar band signal intensities using the neighboring O emission band intensities, which led to detection errors <2% (3 - σ) for both N2 and Ar.

Toward On-Line Slag Composition Analysis: Optical Emissions from Laboratory Electric Arc

Electric arc furnaces and ladle furnaces have an important role in the future of steelmaking where hbox {CO}_2 emissions have to be mitigated to an acceptable level. One way to address this goal is to optimize and improve the current practices by adjusting the chemistry and reactions with material additions or gas injections. These procedures would greatly benefit from on-line slag composition analysis. Since the electric arcs radiate throughout the melting, optical emission spectroscopy is a potential method for such analysis. In this study, optical emissions from the electric arc are measured in a laboratory environment. Dozens of atomic emission lines were correlated with hbox {Cr}_2hbox {O}_3, hbox {Fe}_2hbox {O}_3, hbox {Al}_2hbox {O}_3, hbox {SiO}_2, MnO, MgO, CaO, hbox {CaF}_2, hbox {V}_2hbox {O}_5, and Ni content of the slag together with correlation between hbox {CaF}_2 and molecular optical emission bands of CaF. Optimal spectral resolution for industrial applications was deducted to be between 0.022 and 0.179 nm.

Effect of oxygen vacancy on electronic structure and optical spectra of SrO crystal

Intrinsic defects affect the electronic structure and optical properties of crystals, so their identification is crucial to develop device technology materials. The SrO crystal is an important basic chemical raw material which has attracted special interests as basic heterogeneous catalyst recently. In this work, we used first-principles calculation to study the effect of oxygen vacancy on the electronic structure and optical spectra of SrO crystals. In order to get more accurate results, finite-size correction scheme was employed to correct the defect formation energy and hybrid density functional was performed to reproduce the band gap. We found that V0 introduces a deep impurity level which causing a red shift of the absorption spectrum in SrO crystals. The optical absorption band of F and F+ color centers peak at 2.49eV and 3.06eV, respectively, which are consistent with the experimental results. Meanwhile, the optical emission bands calculated for F and F+ color centers in SrO crystals peak at 2.14 eV and 2.50 eV, respectively. We predict that photoluminescence bands peaks at 554 nm (2.24eV) may be attributed to the F centers and the green emission in SrO crystal (514 nm, 2.53eV) may be caused by F+ centers. Our study will benefit to the apply and design of the novel SrO crystal.

Optical emission bands of Sm2O3 and their link with crystalline defects and 4fd→4fd electronic transitions at UV-Vis region

The Chemical Bath deposition method has been used to synthesize Samarium Oxide (Sm2O3) in previous research where the morphological, structural, and optical properties were studied after thermal annealing treatment at ~1000 °C in the air atmosphere. The present study continues the research on this interesting inorganic material. The average grain size is located at ranges ~22.10 nm to ~28.20 nm, and the optical absorption shows two bands located at ~277 nm (~4.47 eV) and ~408 nm (~3.03 eV) situated in the UV-Vis region. We apply the photoluminescence (PL) spectroscopic technique to examine the emission bands that overlap with the 4fd→4fd electronic transitions in the context of some optical properties at the UV-Vis region. The emission signals present peaks at ~2.52, ~2.55, ~2.56, ~2.60, ~2.63 and ~2.66 eV. Likewise, the Maxwell-Boltzmann statistical model (MBSM) is employed to correlate the native crystalline defects with the cited electronic transitions and emission bands. Finally, the MBSM theoretical curve wraps the emission signals associated with the 4fd→4fd electronic transitions linked with crystalline native defects confirmed by the calculated density of traps. A brief analysis of the chemical kinetics of crystal growth is proposed here.

Physicochemical and DFT studies on new organic Bis-(2-amino-6-methylpyridinium) succinate monohydrate good quality single crystal for nonlinear optical applications

X-ray single-crystal study on the slow evaporation technique grown 2-amino-6-methylpyridinium succinate (2A6MS) exposes its crystal system which belongs to triclinic with centrosymmetric space groupP1¯. A crystal having a dimension of 20 × 8 × 4 mm3 was achieved. 1H NMR spectrum was recorded to investigate the chemical surroundings of various hydrogens in the grown 2A6MS complex and to compliment the X-ray single crystal analysis. FTIR and Raman spectral analyses supported the presence of identified functional groups in the chemical structure. The optical studies by UV–Vis and PL have shown the cut-off wavelength at 348 nm and an occurrence of a high optical emission band at 380 nm under an excitation with 342 nm. The thermal/chemical stability up to 104.3 °C and the absence of phase transformation were confirmed by the TG-DSC study. Vicker’s micro hardness test at room temperature and Chemical etching perceived the mechanical property and the grown-in features of the 2A6MS crystal. SHG study confirmed that the grown 2A6MS crystal has SHG which is very well compared with the standard KDP crystal. Density functional theory (DFT) computation was used on B3LYP/6–311++G (d, P) basis set to optimize molecular geometry, HOMO-LUMO energies, Mulliken population analyses, molecular electrostatic potential, NBO, and first order hyperpolarizability.

Dual photoluminescent blue and green emission bands by the enantiopure (S)-(+)-1-(4-bromophenyl)-N-1-phenylethylmethanimine crystals

Herein, the analysis of the (S)-(+)-1-(4-bromophenyl)-N-1-phenylethylmethanimine organic material in solid state is reported, i.e., the crystal structure, molecular packing, morphological and optical analysis, as well as the correlation of these parameters are presented. The crystalline phase and spatial group were established by X-ray Diffraction (XRD) studies. The surface morphology of the crystal was recorded by Scanning Electron Microscopy (SEM) technique. SEM images showed a packing with dense plates stacked and fragmented. The UV–Vis spectral analysis was registered in the ~350–700 nm (~4.13–1.77 eV) range. The band gap energy (Eg) was determined by the Tauc model and located at Eg ~3.45 eV. Two experimental emission bands were recorded by Photoluminescence (PL) at room temperature in the Vis-region located in the ~415 nm (~2.88 eV) and ~558 nm (~2.22 eV) ranges. These emission signals were identified as blue (BE) and green (GE) emission bands, respectively. By applying the theoretical Maxwell-Boltzmann model as a proxy to considering crystalline defects as fixed particles, the optical emission bands of PL were calculated suggesting that the crystalline defects (e.g., vacancies and molecular interstices) generated the GE and BE bands. The experimental-theoretical results have values very close to each other when comparing the relative maxima, as it is presumed that this optical phenomenon is generated by the crystalline defects. A Raman spectroscopy study was also performed.

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes.

In a systematic survey of luminescent bis(terdentate) osmium(II) complexes, a tipping point involving a reversal in photophysical tuning is observed whereby increasing stabilization of the ligand-based lowest unoccupied molecular orbital (LUMO) results in a blue shift in the optical absorption and emission bands. The complexes [Os(N^N'^N″)2]2+ [N^N'^N″ = 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine (Os1), 2,6-bis(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os2), 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyridyl (Os3), 2-(pyrid-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os4), 2-(pyrazin-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyridine (Os5), and 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyrazinyl (Os6)] have been prepared and characterized, and all complexes display phosphorescence ranging from the orange to near-IR regions of the spectrum. Replacement of the central pyridine in the ligands of Os1 by the more π-accepting pyrazine in Os2 results in a 55 nm red shift in the triplet metal-to-ligand charge-transfer-based emission band, while a larger red shift of 107 nm is observed for the replacement of one of the triazole donors in the ligands of Os1 by a second pyridine ring in Os3 (λemmax = 702 nm). Interestingly, replacement of the central pyridine ring in the ligands of Os3 by pyrazine (Os4,λemmax = 702 nm) fails to result in a further red shift in the emission band. Reversal of the relative positions of the pyridine and pyrazine donors in Os5 (λemmax = 733 nm) compared to Os4 does indeed result in the expected red shift in the emission with respect to that for Os3 based on the increased π-acceptor character of the ligands present. However, an inversion in emission tuning is observed for Os6, in which the incorporation of a second pyrazine donor in the ligand architecture results in a blue shift in the optical absorption and emission maxima (λemmax = 710 nm). Electrochemical studies reveal that while incorporating pyrazine in the ligands indeed results in an expected anodic shift in the first reduction potential through stabilization of the ligand-based LUMO, there is also a concomitant anodic shift in the OsII/OsIII-based oxidation potential. This stabilization of the metal-based highest occupied molecular orbital (HOMO) thus nullifies the effect of stabilization of the LUMO in Os4 compared to Os3, resulting in these complexes having coincident emission maxima. For Os6, stabilization of the HOMO through the incorporation of two pyrazine donors in the ligand structure now exceeds stabilization of the LUMO, resulting in a larger HOMO-LUMO gap and a counterintuitive blue shift in the optical properties in comparison with those of Os5. While it is known that the replacement of ligands (e.g., replacing bipyridyl with bipyrazinyl) can result in a larger HOMO-LUMO energy gap through greater stabilization of the HOMO, these results importantly allow us to capture the tipping point at which this inversion in photophysical tuning occurs. This therefore enables us to explore the limits available in emission tuning with a relatively simple and minimalist ligand structure.

Coexistence of interface states and confined electronic levels contribution for the light emission of Si nanocrystals embedded in SiO2

This article shows results on photoluminescence measurements of Si nanocrystals embedded in a SiO2 matrix. Photoluminescence spectra were obtained as functions of both temperature (10–510 K) and excitation power (0.01–100 mW). Optical emission bands with interesting behavior as temperature was raised were observed, and a model to explain these bands considering contributions from interface states associated with SiOx and Si–O–Si units, whose emissions are located around 1.32 eV, 1.41 eV and 1.57 eV, and from quantum confinement states associated with the Si nanocrystals, was proposed.

Trivalent ion mediated abnormal growth of all-inorganic perovskite nanocrystals and their divergent emission properties.

In this work, a new trivalent ion-mediated one-pot synthetic protocol is reported to create two well-defined optical absorbance and photoluminescence (PL) emissions in all-inorganic halide perovskite nanocrystals (NCs). The foreign M3+ cations (M = Bi, Al, In), typically from BiBr3, BiFeO3, BiCl3, AlBr3 or InBr3, function as capping ligands for generating a growth-constrained thinner nanoplatelet (NPL) population displaying the quantum confinement effect. The formation mechanism of the growth-constrained NPLs is proposed based on density functional theory (DFT) on the different slab energy of the representative NPLs achieved in the presence of Bi3+ ions and the density of states (DOS) of the supposed bulk perovskites. Notably, the formation of two groups of NCs with different sizes allows for the generation of dual optical absorbance and PL emissions. The influence of the M : Pb molar ratios on the precursors is systematically elucidated, from which the relative intensity and position of each PL emission can be fine-tuned. By virtue of the representative NPLs with well-defined green and blue emissions, the M3+-assisted synthetic protocol provides a facile and cost-effective route for producing unique NCs and nanostructures for optoelectronic device applications.

Fabrication and determination of growth regimes of various Pd NPs based on the control of deposition amount and temperature onc-plane GaN

Abstract

Growth, spectral, mechanical, thermal and dielectric studies of undoped and rhodamine-B doped l-alanine acetate crystals

Single crystals of undoped and rhodamine-B doped l-alanine acetate have grown from solution by slow evaporation method at room temperature (30 °C). The title samples were synthesized and purified by repeated re-crystallization process. Solubility of the samples in water was found at different temperatures. The crystals were characterized by single crystal X-ray diffraction and Fourier Transform Infrared Spectroscopic (FTIR) analysis. The range and percentage of optical transmission was ascertained by recording UV–vis–NIR spectra and the optical band gap was determined. The second harmonic generation behavior of the samples was tested by Kurtz–Perry powder technique. Mechanical hardness, yield strength and stiffness constant were estimated by Vickers microhardness method. Laser damage threshold values were found out using Nd:YAG laser for the grown crystals. EDAX analysis was done to identify elements present in the undoped and rhodamine-B doped l-alanine acetate crystals. Dielectric constant and dielectric loss of the samples were estimated to understand the polarization processes and insulating behavior in the samples. TG/DTA studies were carried out to find the thermal stability and photoluminescence spectra were recorded for the samples to find the optical emission bands.

Preparation of Highly Flexible SiC Nanowires by Fluidized Bed Chemical Vapor Deposition

High flexible SiC nanowires with diameters in the range of 10 to 50 nm and lengths of several hundred micrometers to several millimeters are synthesized using a novel catalyst-assisted fluidized bed chemical vapor deposition method. Methyltrichlorosilane (MTS) is used as source material and particles containing cobalt were used as catalyst. The fluidized bed is specially designed to form a perpendicular uneven temperature distribution. Suspended nanosized liquid catalyst droplets are produced at middle high temperature zone and SiC nanowires are formed in situ on the catalyst droplets then accumulated at the upper part of fluidized bed. The nanowires exhibit a single crystal feature with some stacking faults. Transmission electron microscopy (TEM) analysis verifies a growth direction along the <111> axis of the nanowires. A blue shift optical emission band at about 420 nm is detected using photoluminescence spectroscopy. From the high-resolution TEM investigation, a nanoscale smooth plane between the nanowire and the catalyst tip is observed and the two phases exhibit highly epitaxial growth interface. The growth process of the nanowires is discussed and a possible formation mechanism is proposed.

Enhancement of the luminescence intensity by co-doping Mn2+ into Er3+-doped SrAl2O4

Structural and optical properties of erbium- and manganese-doped strontium aluminates (SrAl2O4) phosphor materials synthesized by a solid state reaction were investigated. The samples presented the fundamental optical transitions due to Er3+ and Mn2+ which are typical features of the well-diluted doping process. A significant enhancement of the Er3+ optical emission band at 1530nm was observed when the matrix is co-doped with Mn. Photoluminescence intensity under ultraviolet excitation was three times larger as compared to samples without Mn content. A model of energy transfer mechanism from Mn2+ to Er3+ ions due to optical energy matching is proposed to explain the experimental results. This result, presented first time, can be applied as useful tool for developments in optical communications.

Formation of size controlled silicon nanocrystals in nitrogen free silicon dioxide matrix prepared by plasma enhanced chemical vapor deposition

This paper reports the growth of silicon nanocrystals (SiNCs) from SiH4–O2 plasma chemistry. The formation of an oxynitride was avoided by using O2 instead of the widely used N2O as precursor. X-ray photoelectron spectroscopy is used to prove the absence of nitrogen in the layers and determine the film stoichiometry. It is shown that the Si rich film growth is achieved via non-equilibrium deposition that resembles a interphase clusters mixture model. Photoluminescence and Fourier transformed infrared spectroscopy are used to monitor the formation process of the SiNCs, to reveal that the phase separation is completed at lower temperatures as for SiNCs based on oxynitrides. Additionally, transmission electron microscopy proves that the SiNC sizes are well controllable by superlattice configuration, and as a result, the optical emission band of the Si nanocrystal can be tuned over a wide range.

Cold large-diameter plasma jet near atmospheric pressure produced via a triple electrode configuration

In this letter, a triple electrode discharge configuration is presented for producing large-diameter plasma jet near atmospheric pressure. Different from various cold atmospheric pressure plasma jets via concentric dielectric barrier discharge (DBD) configurations, the novel kind of large-diameter plasma jet generates with much larger dimension in diameter in pure argon or Ar/N2 mixture near atmospheric pressure (750 torr). The voltage and current waveform (I–V) measurement indicates that the discharge composes of two consequent sections, one of which occurs as coaxial DBD mode while the other forms large-diameter plasma jets. The overall temperature of the plasma is determined to be about 300 K by fitting the plasma optical emission bands of N2(B-C) and OH(A-X). Therefore the plasma is believed as cold as those atmospheric pressure plasma jets with concentric DBD configurations.

XAFS and XEOL of tetramesityldigermene – An electronic structure study of a heavy group 14 ethylene analogue

Digermene, the germanium analogue of ethylene, has a multiple bonding motif that differs greatly from that of alkenes and exhibits no pure σ or π type bonds. The electronic structure of digermenes is difficult to study experimentally due to their reactivity, and is computationally challenging because of their shallow potential energy surfaces. Using X-ray absorption near edge structures at both the germanium K and L edges we have been able to directly probe the unoccupied electronic states, or the lowest unoccupied molecular orbital (LUMO), and LUMO+ etc. in the Ge=Ge bond of tetramesityldigermene. We have demonstrated that the LUMO, LUMO+, etc. are composed of hybrid Ge 4s and 4p orbitals. Additionally, our data suggest that the LUMO exhibits relatively more Ge 4s character, whereas the LUMO+ and LUMO+2 exhibit relatively more Ge 4p character. An X-ray excited optical luminescence study of Ge2Mes4 revealed one broad optical emission band at 620 nm, which is significantly red shifted compared to the known energy gap of this molecular germanium compound.

Optical emission of InAs nanowires

Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende–wurtzite alternating layers, and to the donor–acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature.

The synthesis and spectral investigation of a novel highly water-soluble, aggregation-free antimony(V)-phthalocyanine absorbing light in optical therapeutical window

A novel antimony–phthalocyanine, [Sb(H3tsppc)(OH)2], where H3tsppc denotes monodeprotonated tetrakis{(2′,6′-dimethyl-4′-sulfonic acid)phenoxyl}phthalocyaninate, has been synthesized through sulfonation of [Sb(tppc)(OH)2]+ (tppc denotes tetrakis{(2',6'-dimethyl)phenoxyl}phthalocyaninate) in concentrated sulfuric acid. This compound is highly soluble in water (ca. 4×10−2M) without surfactant or alcohol. Moreover, it has been found free from aggregation in water up to almost 10−4M, unlike its copper and metal-free analogues, and show an intense optical absorption and emission band in optical therapeutical window (700–800nm). The axial hydroxyl groups play a crucial role in disaggregation of the antimony derivative in water.

Visible-Light-Induced Photosplitting of Water over γ′-Fe4N and γ′-Fe4N/α-Fe2O3 Nanocatalysts

The application of γ′-Fe4N, a noble-metal-free, low-cost catalyst, in the photosplitting of neat water into stoichiometric amounts of H2 and O2 under visible-light irradiation is reported for the first time. The catalyst showed optical absorption and photoluminescence emission bands in the entire visible region. The photocatalytic water-splitting activity was wavelength-dependent, the quantum efficiency for H2 evolution being ca. 1.7 and 0.7% at excitation wavelengths of 450 and 500 nm, respectively. Addition of electron donor/acceptor sacrificial reagents considerably affected the yield and stoichiometry of H2 and O2. At the same time, the product yield increased in a composition-dependent manner for (γ′-Fe4N)x + (α-Fe2O3)1–x nanocomposites. This activity augmentation is ascribed to the better dispersion of the active component γ′-Fe4N and also to the availability of more active surface sites at Fe4N/Fe2O3 contacts. Moreover, the proximity of the valence band potential of the component photosystems promo...