Characteristic Emission Lines Research Articles

The in-situ excitation on internal electrode of DBD-OES system for cadmium sensitive detection

The utilization of microplasma excitation sources in miniature systems offers reliable tools for the portable detection of heavy metal contamination. Dielectric barrier discharge (DBD)-based optical emission spectrometry has emerged as a significant technique for the detection of metal ions recently. Here, a sensitive miniature DBD-OES system for cadmium enrichment and detection is developed. A piece of ceramic tube with abundant hydroxyl (-OH) and alumina (AlO) functional groups is used for cadmium pre-concentration and serve as a part of the internal electrode of the DBD. When microplasma generates, the cadmium on the surface of the internal electrodes is desorbed and in-situ excited, and the characteristic emission line of cadmium appears. The mechanism of cadmium excitation on ceramic tube, the characteristics of the microplasma excitation and the enrichment on the internal electrode are discussed. Under the working conditions, the emission intensity of cadmium shows linear relationship within the range of 0.5–8 μg L−1, and the limit of detection (LOD) is 0.3 μg L−1. Finally, a series of water samples are determined to validate the applicability of the present system.

Atmospheric pressure plasma jet: Green technology advancements for metals deposition potential

This study explored the utilization of an atmospheric pressure plasma jet (APPJ) for the deposition of metal layers, employing Ar + 2 % H2 as the working gas. The research focuses on three distinct metals - silver (Ag), copper (Cu), and nickel (Ni). Through the application of optical emission spectroscopy, significant peaks of Ar-related and hydrogen-alpha (Hα) species are observed, accompanied by atomic characteristic emission lines specific to Ag, Cu, and Ni, respectively. The XRD examination indicates the successful deposition of metal layers onto the substrates, a confirmation supported by the EDS line scan. Examination of the surface morphology reveals that the metal particles have clustered together, creating a porous structure. The resistivity measurement obtains the values of 5.18, 3.81, and 9.21 μΩ-cm for Ag, Cu, and Ni layers, respectively. Moreover, the paper presents a proposed mechanism for depositing metallic conductive layers using an atmospheric pressure plasma jet (APPJ), elucidating the complex processes inherent in this novel technique.

The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions

Rapid rotation and nonradial pulsations enable Be stars to build decretion disks, where the characteristic line emission forms. A major but unconstrained fraction of Be stars owe their rapid rotation to mass and angular momentum transfer in a binary. The faint, stripped companions can be helium-burning subdwarf OB-type stars (sdOBs), white dwarfs (WDs), or neutron stars. We present optical/near-infrared Center for High Angular Resolution Astronomy (CHARA) interferometry of 37 Be stars selected for spectroscopic indications of low-mass companions. From multiepoch H- and/or K-band interferometry plus radial velocities and parallaxes collected elsewhere, we constructed 3D orbits and derived flux ratios and absolute dynamical masses of both components for six objects, quadrupling the number of anchor points for evolutionary models. In addition, a new wider companion was identified for the known Be + sdO binary 59 Cyg, while auxiliary Very Large Telescope Interferometer/GRAVITY spectrointerferometry confirmed circumstellar matter around the sdO companion to HR 2142. On the other hand, we failed to detect any companion to the six Be stars with γ Cas–like X-ray emission, with sdOB and main-sequence companions of the expected spectroscopic mass being ruled out for the X-ray-prototypical stars γ Cas and π Aqr, leaving elusive WDs as the most likely companions, as well as a likely explanation of the X-rays. No low-mass main-sequence close companions were identified for the other stars.

NIR emission from Nd3+ doped Sr3WO6 distorted triclinic phosphor

The article describes the synthesis and spectroscopic properties of Sr3WO6:Nd3+ NIR emitting phosphor. The X-ray diffraction analysis confirms the formation of the compound. The Rietveld refinement analysis indicates that the crystal structure is a distorted triclinic system with space group P–1 (C1). The band bap of Sr3WO6:Nd3+ is reported as ≈3 eV from the Kubelka–Munk equation. The phosphor is excited at the wavelength of 824 nm of NIR spectrum. The excitation spectrum is spread over from the visible to the NIR region. The PL emission is obtained in the NIR region with a prominent characteristic emission line at 1083 nm. The obtained PL emission is due to the occupancy of Nd3+ ions in Sr2 2+–O and Sr6 2+–O lattice sites. The quenching of luminescence intensity is due to the exchange interaction mechanism between the host Sr2+ site and dopant Nd3+ ion. As per spectroscopic analysis, Sr3WO6:Nd3+ phosphor may be considered as a promising candidate towards solid–state laser applications.

Copper signal characteristics using collinear LS-DP-LIBS for underwater measurement

The collinear long-short double-pulse laser-induced breakdown spectroscopy (LS-DP-LIBS) was employed in the detection of underwater copper samples. Discrete emission lines were obtained using LS-DP-LIBS with an appropriate delay between two pulses, while characteristic emission lines were covered by continuous background and noise using LIBS with a single pulse. In the condition of LS-DP-LIBS, signal characteristics of the measured spectra at different experimental parameters including long-pulse width, lens-to-sample distance (LTSD), and long-pulse energy have been investigated to determine the optimal condition. The results indicated that the long-pulse width and the long-pulse energy were closely related to the formation of a cavitation bubble, thus affecting the plasma state and signal characteristics for underwater measurement. The parameter of the LTSD imposed an effect on the spectral signal through changing the ablation mass of the sample and the plasma temperature. The experimental results demonstrated the feasibility of the underwater measurement of metal samples using the collinear LS-DP-LIBS and showed a significant signal improvement through this method. With further development, it is of great potential to apply this new method based on LIBS to ocean exploration.

Taking a break: Paused accretion in the symbiotic binary RT Cru

Symbiotic binaries sometimes hide their symbiotic nature for significant periods of time. There is mounting observational evidence that, in symbiotics that are powered solely by the accretion of the red giant’s wind material onto a white dwarf, without any quasi-steady shell burning on the surface of the white dwarf, the characteristic emission lines in the optical spectrum can vanish, leaving the semblance of an isolated red giant spectrum. Here we present compelling evidence that this disappearance of optical emission lines from the spectrum of RT Cru in 2019 was due to a decrease in the accretion rate, which we derived by modeling the X-ray spectrum. This drop in accretion rate leads to a lower flux of ionizing photons and thus to faint or absent photoionization emission lines in the optical spectrum. We observed the white dwarf symbiotic RT Cru with XMM-Newton and Swift in X-rays and UV and collected ground-based optical spectra and photometry obtained over the last 33 yr. This long-term coverage shows that, during most of the year 2019, the accretion rate onto the white dwarf was so low, Ṁ = (3.2 ± 0.06) × 10−11 M⊙ yr−1 (d/2.52 kpc)2, that the historically detected hard X-ray emission almost vanished, the UV flux faded by roughly 5 mag, the U, B, and V flickering amplitude decreased, and the Balmer lines virtually disappeared from 2019 January through March. Long-lasting low-accretion episodes such as the one reported here may hamper the chances of RT Cru experiencing a nova-type outburst despite the high mass of the accreting white dwarf.

In-situ deposition of lead halide perovskite quantum dots in mesoporous YF3:Eu3+ matrices with multi-wavelength emission and remarkably enhanced stability

Lead halide perovskite quantum dots (CsPbX3 PQDs, X = Cl, Br and I) have aroused wide concerns due to their outstanding optoelectronic characteristics. However, the simultaneous promotion of both high luminescence performance and brilliant stability is still a major challenge for their practical applications. Herein, Eu3+ doped YF3 nanospheres with hollow mesoporous structure are used to construct reactors for in-situ depositing CsPbX3 QDs through hot injection method. The as-synthesized CsPbBr3+YF3:Eu3+ nanocomposites exhibit multi-wavelength emission consisting of blue from self-trapped excitation (STE) emission of YF3 host, green from CsPbBr3 excitonic peak and red from characteristic emission lines of Eu3+. Besides, CsPbX3+YF3:Eu3+ composites with different halide compositions have been prepared and show multicolor emission with a wide color gamut. It is interesting to note that the stability of CsPbBr3+YF3:Eu3+ nanocomposites is remarkably enhanced under humid air, UV irradiation, and high temperature conditions compared to pristine CsPbBr3 QDs. This study provides new insights to realize stable CsPbX3 QDs-based multifunctional materials with multi-wavelength emission by combining with rare earth ions doped mesoporous materials and CsPbX3 QDs.

Angular distribution of characteristic X-rays following electron impact ionization

In this paper, we present a theoretical study of the X-ray fluorescence emission after vacancy of K-shell due to electron impact ionization. In particular, we focus on the angular distributions of the characteristic Kα emission lines following this process. Rh was chosen for the analysis since it is a common element in X-ray tube anodes. In this analysis we also considered some elements along the period-4, i.e., Ni, Cu and Co as case-studies. In doing so, we studied the magnetic sub-level population of the ionized states, which is directly related to the angular distribution of the emission. A relative low angular distribution for the Kα emission of Rh of 0.5% was observed, which makes the assumption of isotropic emission correct for most studies. Moreover, a comparison with the respective angular emission for adjacent elements in the fourth period of the periodic table shows that this isotropy is attributed to a small total angular momentum of the resulting configurations after ionization, as well as to opposite angular distributions of the various transitions, which average to a maximum of 0.7% angular asymmetry in Ni.

In situ simultaneous quantitative analysis multi-elements of archaeological ceramics via laser-induced breakdown spectroscopy combined with machine learning strategy

With the characteristics of precious, rare and non-renewable, archaeological ceramics cannot be used for destructive analysis and testing. Valuable physical and chemical information can be obtained through scientific micro damage analysis of precious pottery, which plays a positive role in the protection of ceramics and archaeological research. In this study, LIBS spectroscopy combined with sequential backward selection-random forest regression (SBS-RFR) algorithm was proposed for simultaneous quantitative analysis of multi-elements in ceramic samples. Firstly, the experimental conditions for LIBS spectrum acquisition of ceramic samples were optimized, including delay time, laser pulse energy and cumulative times, and the characteristic emission lines of typical elements in LIBS spectra of ceramic samples were identified based on national institute of standards and technology (NIST) database. Four different spectral preprocessing methods are used to preprocess LIBS spectral data to find a better preprocessing method. And then, SBS algorithm is applied to eliminate irrelevant or redundant feature variables of LIBS spectrum. SBS-RFR calibration model is constructed based on the screened input variables to realize the rapid determination of multi-element content of ceramic samples. To further verify the prediction performance of the SBS-RFR calibration model, its prediction performance is compared with several other models. The results show that SBS-RFR model has better prediction performance than partial least squares regression (PLSR), support vector machine (SVM), and random forest regression (RFR), of which the R2 values of prediction set are all over or close 0.98, and the RMSE values for Mg, Al, Ca and Fe are 0.3954%, 0.4627%, 0.2532% and 0.3791% respectively. This study shows that LIBS technology combined with SBS-RFR algorithm is a feasible method for the quantitative analysis of elements in ceramic samples.

Insight into the spectroscopic behavior of Dy3+‐substituted and Li+ charge–compensated molybdate phosphors

AbstractEfficient utilization of phosphors in solid‐state lighting and phosphor‐converted light‐emitting diodes demands high emission intensity, narrow size distribution, and tunable luminescence. Here in this work, un‐doped and Li+ co‐doped CaMoO4:Dy3+ nanoparticles are synthesized via modified reflux method in ethylene glycol medium at 130°C. The host shows broad dual band emission centered in blue and green regions endowed by charge transfer and defects. Upon Dy3+ doping, the host‐to‐dopant energy transfer causes the CaMoO4:Dy3+ nanoparticles to exhibit characteristic emission lines from Dy3+. The Commission Internationale de L'Eclairage (CIE 1931) chromaticity coordinates for the prepared phosphors are estimated and found to lie in the nearly white region of color space. The light output as well as excited state lifetimes are successfully improved by lithium co‐doping by virtue of reduced charge compensating defects and sensitization via oxygen‐related defects. The positron annihilation studies show that all the lithium concentration co‐doped for charge compensation is merely helping in the removal of cations. This work shows the role of lithium co‐doping and its optimum concentration in improving the optical properties of phosphors.

Neural network-based classification of X-ray fluorescence spectra of artists’ pigments: an approach leveraging a synthetic dataset created using the fundamental parameters method

X-ray fluorescence (XRF) spectroscopy is an analytical technique used to identify chemical elements that has found widespread use in the cultural heritage sector to characterise artists' materials including the pigments in paintings. It generates a spectrum with characteristic emission lines relating to the elements present, which is interpreted by an expert to understand the materials therein. Convolutional neural networks (CNNs) are an effective method for automating such classification tasks—an increasingly important feature as XRF datasets continue to grow in size—but they require large libraries that capture the natural variation of each class for training. As an alternative to having to acquire such a large library of XRF spectra of artists' materials a physical model, the Fundamental Parameters (FP) method, was used to generate a synthetic dataset of XRF spectra representative of pigments typically encountered in Renaissance paintings that could then be used to train a neural network. The synthetic spectra generated—modelled as single layers of individual pigments—had characteristic element lines closely matching those found in real XRF spectra. However, as the method did not incorporate effects from the X-ray source, the synthetic spectra lacked the continuum and Rayleigh and Compton scatter peaks. Nevertheless, the network trained on the synthetic dataset achieved 100% accuracy when tested on synthetic XRF data. Whilst this initial network only attained 55% accuracy when tested on real XRF spectra obtained from reference samples, applying transfer learning using a small quantity of such real XRF spectra increased the accuracy to 96%. Due to these promising results, the network was also tested on select data acquired during macro XRF (MA-XRF) scanning of a painting to challenge the model with noisier spectra Although only tested on spectra from relatively simple paint passages, the results obtained suggest that the FP method can be used to create accurate synthetic XRF spectra of individual artists' pigments, free from X-ray tube effects, on which a classification model could be trained for application to real XRF data and that the method has potential to be extended to deal with more complex paint mixtures and stratigraphies.

Indicators of upcoming electric breakdown in a pyroelectric accelerator

This paper describes indicators that can be used to monitor the operating mode of a pyroelectric accelerator. It is shown that the ratio of the characteristic X-ray emission lines from the target and the vacuum chamber walls is very sensitive to the state of the accelerator. Also, the peak to total count rate ratio in the electron spectrum exhibits similar properties. These parameters change sharply ahead of the electric breakdown and are very sensitive to the residual gas pressure level. Monitoring these indicators during the accelerator operation provides a fine tool aiding the implementation of pyroelectric technology for stable and reliable charged particle generation and acceleration.

Quantitative laser-based x-ray fluorescence and particle-induced x-ray emission

In this work, we demonstrate the feasibility of quantitative laser-based x-ray fluorescence (XRF) combined with particle-induced x-ray emission (PIXE) (called XPIF for x-ray and particle-induced fluorescence) spectroscopy analysis for elemental composition in solid samples. A multi-hundred TW laser system accelerated protons and produced x-rays that were impinging on solid samples, inducing characteristic line emissions of the elements contained in the material. The x-ray yield obtained from the characteristic emissions for each element can be related to its mass concentration using both the thick PIXE and thick XRF formalism. This is performed by using of an iterative numerical procedure. We tested the validity of our method on three homogeneous metallic materials, stainless steel, bronze and brass. The mass proportions of these samples retrieved by our analysis (XPIF) is within the errors bars compared with a commercial energy dispersive x-ray spectrometer.

Pressure-driven configurational crossover between 4f7 and 4f65d1 States – Giant enhancement of narrow Eu2+ UV-Emission lines in SrB4O7 for luminescence manometry

Accurate, fast, and non-invasive methods for the determination of the local pressure magnitude are crucial for the investigation of the physical and chemical behavior of materials at the extreme conditions of high pressure. A promising method for remote operando pressure measurements is luminescence manometry. However, a limiting bottleneck for high-pressure readout is the usually occurring quenching of the emission signal of the luminescent sensor material upon compression. In this work, we reported for the first time the pressure-induced intensity enhancement (by 3 orders of magnitude) of the 4f7(6P7/2)→4f7 (8S7/2) emission line of Eu2+ in the UV range due to pressure-induced configurational crossover between the excited 4f65d1 and 4f7 energy levels in SrB4O7 host. The peak centroid of the narrow 4f7 → 4f7 transition exhibits a significant red-shift (∼ -12.84 cm−1 GPa−1; 0.17 nm GPa−1) with simultaneous temperature independence of the line position (4.8·10−4 nm K−1). The pressure sensitivity of the proposed system is competitive to the so far well-established luminescent pressure sensors based on Al2O3:Cr3+ (ruby) and SrB4O7:Sm2+ with characteristic narrow line emission in the red range, and offers an alternative spectral range in parallel with an intensity enhancement at higher pressures. This novel pressure gauge may significantly improve the accuracy of the remote pressure measurements and open up new horizons for materials science research at even higher pressures.

Investigation on photoluminescence properties of MWCNTs@Gd2O3: RE3+ (RE = Eu, Tb, and Tm) hybrid nanocomposites

A facile synthesis of rare earth (RE3+) activated gadolinium oxide (Gd2O3) decorated on the surface of multiwall carbon nanotubes (MWCNT), i.e., MWCNTs@Gd2O3: RE3+ (RE = Eu, Tb, and Tm) have been carried out. The X-ray diffraction patterns and scanning electron microscope (SEM) micrographs of as-prepared nanocomposites confirm the homogeneous dispersion of the nanocomposites. The emission spectrum of MWCNTs@Gd2O3:Eu3+ nanocomposite exhibits the characteristic emission lines of Eu3+ at 590 nm and 610 nm with the radiation of 254 nm. MWCNTs@Gd2O3:Tb3+ nanocomposite displays an intense green emission at 547 nm, while MWCNTs@Gd2O3:Tm3+ nanocomposite shows a strong blue emission at 457 nm under ultra-violet (UV) excitation of 360 nm. The calculated values of emission lifetimes in the studied phosphors could attribute to more radiative relaxation. Henceforth, the results affirm that these spectral engineered luminescent materials may envision prospective applications in fluorescent imaging, bio-separation, fluorescent lamps, and display devices, etc.

Time-Resolved Imaging of Femtosecond Laser-Induced Plasma Expansion in a Nitrogen Microjet

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation led to plasma generation with a characteristic spectral line emission at 391 nm. By following the emitted signal with a detection system based on an intensified charge-coupled device (ICCD) we captured the two-dimensional spatial evolution of the photo-excited nitrogen ions with a temporal resolution on the nanosecond time scale. We fabricated the micronozzle on a fused silica substrate by femtosecond laser micromachining. This technique enabled high accuracy and three-dimensional capabilities, thus, providing an ideal platform for developing glass-based microfluidic structures for application to plasma physics and ultrafast spectroscopy.

Effects of the refractive index of the X-ray corona on the emission lines in AGNs

ABSTRACT X-ray reflection from an accretion disc produces characteristic emission lines allowing us to probe the innermost regions in active galactic nuclei. We investigate these emission lines under a framework of Riemannian geometrical optics where the corona has a refractive index of n ≠ 1. The empty space outside is a vacuum with n = 1. The Kerr metric is modified to trace the light rays that are bent due to not only the gravity of the black hole but also the effects of coronal plasma dependent on n. The choice of n alters the null geodesics, producing the effect which is analogous to the light deflection. For the corona with n > 1, the disc on the far side within the corona covers a larger area on the observer’s sky, enhancing the blue wing of the line and producing more flux difference between the blue peak and extended red tail. The inverse effects are seen when n < 1. Moreover, the corona with n > 1 and n < 1 could induce extra shifts in the blue wing (Δgmax) to higher and lower energy, respectively. These effects are more prominent when the inclination angle is ≳60° and the corona extends to ≳5rg. To obtain the deviation of the line shift of Δgmax ≳ 0.01, the difference between the refractive index of the corona and that of the empty space must be $\Delta n \gtrsim 0.5{{\ \rm per\ cent}}$. Finally, the lensing corona can influence the arrival time of photons that may affect the observed variability of these emission lines.

An Endpoint Detection System for Ion Beam Etching Using Optical Emission Spectroscopy

An ion beam etching system with etching endpoint detection (EPD) capability based on optical emission spectroscopy (OES) was conceived, built, and tested. An expansion chamber was added on the right side of the etching chamber to fix the optical detector for in-situ detecting. In this system, the optical detector was mounted on a seven-shaped bracket, which was fixed by two straight guides, thus the position of the optical detector could be adjusted arbitrarily to collect the emission spectrum generated by the sample during the etching process. The signal was transmitted by optical fiber to the computer for processing, and the etching endpoint could be detected after analyzing the data. Firstly, we used simple substances (Al, Cr, Si, and Mg) to analyze the feasibility of the system and determine the best position of the optical detector. In addition, we also tested the detection limit of the system. Finally, a complex multilayer film sample with different materials was tested, and the results showed that the system could clearly detect the characteristic emission lines of different layers and had a good real-time performance and excellent endpoint detection capabilities.

Luminescence Properties of Gd2(MoO4)3 Modified with Sm(III) and Tb(III) for Potential LED Applications

Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd1.97−y SmyTb0.03(MoO4)3 (y = 0.01–0.11, step 0.02) and Gd1.95−xSm0.05Tbx(MoO4)3 (x = 0.01–0.09, step 0.02), were synthesized and characterized by X-ray diffraction, UV-Vis spectroscopy, scanning and transmitting electron microscopy (SEM, TEM) as well as photoluminescence spectroscopy. The effect of the doping content of Tb/Sm was followed. The unit cell parameters for Gd1.97−ySmyTb0.03(MoO4)3 and Gd1.95−xSm0.05Tbx(MoO4)3 changed with the increase in the Tb/Sm content. The microstrain values also increased, proposing an increased concentration of defects. The mean particle size was estimated to be approximately 0.6 µm. Based on a Williamson–Hall plot, the size of the crystallites was determined to be in the range of 42–60 nm for modified and pure Gd2(MoO4)3 samples, respectively. The samples excited at 406 nm exhibited characteristic emission lines of Sm (485, 555, 646 nm). The host material Gd2(MoO4)3 emission in visible light was explained by the crystal structure defects, namely, oxygen vacancies. The CIE x/y color coordinates of the phosphors were determined and the related points were located in the green-yellow/pale yellow region of the visible light. The excited state lifetimes were determined for both groups of the samples, showing values in the millisecond range and indicating the samples as promising phosphors.

Nanosecond laser-assisted micro-scribing of a copper film on a dielectric material with laser-induced breakdown spectroscopy based monitoring

Pulsed laser-based material removal is a preferred micro-scribing technique for Copper (Cu) cladded onto an insulating substrate, such as a flame-retardant glass-reinforced epoxy resin (FR4), because of the less thermal diffusion as well as the process flexibility. This paper reports the pulsed laser-assisted micro-scribing of Cu (35 µm) from a dielectric material. The process was monitored by laser-induced breakdown spectroscopy technique (LIBS). For the complete removal of Cu from the substrate material, multiple laser scans were required. The Cu I line intensity in the LIBS spectra was decreasing with an increase in the microchannel depth. During the final laser scan, the FR4 substrate was getting ablated, and in the LIBS spectra, the characteristic emission lines from the substrate elements such as Calcium (Ca), Aluminum (Al), Sodium (Na) and Silicon (Si) were observed. The depth for a single laser pulse was estimated from a theoretical model, including the melt ejection due to the recoil pressure. Approximate microchannel depth was predicted based on the theoretical simulation.