Spectral Emission Intensity Research Articles

Enhancing silicon spectral emission in LIBS using Tesla coil discharge

Laser-induced breakdown spectroscopy (LIBS) is a powerful technique for elemental analysis, offering rapid analysis, minimal sample preparation, wide elemental coverage, and portability. To enhance the detection sensitivity of LIBS, increasing the spectral emission intensity is crucial. This paper explores the use of Tesla coil (TC) discharge as an alternative to spark discharge in silicon LIBS. The study examines the influence of TC discharge on both time-integrated and time-resolved spectra, with and without TC discharge; the corresponding electron temperature and density are obtained. The results show that TC discharge significantly amplifies the spectral intensity, improving signal sensitivity in LIBS analysis. Specifically, in the laser energy range from 7.4 to 24.0 mJ, TC discharge increased the average spectral line intensities of Si (II) 385.60 nm and Si (I) 390.55 nm by factors of 8.4 and 5.1, respectively. Additionally, the average electron temperature and density were enhanced by approximately 3.2% and 4.2%, respectively, under TC discharge. The advantages of TC discharge include higher energy deposition, extended discharge duration, reduced electrode erosion, and enhanced safety. This research contributes to advancing LIBS technology and expanding its applications in various fields.

Double perovskite CaSrMSbO6(M = La, Gd, Y): Bi3+ phosphors for multifunctional application

Bi3+-doping luminescent materials have recently evoked considerable interest in versatile applications. In this work, we have developed a series of Bi3+-activated CaSrMSbO6(M = La, Gd, Y) phosphors with double perovskite structures, exhibiting blue emission from 350 nm to 500 nm. The emission spectral position and intensity of Bi3+ ions can be tuned by changing excitation wavelength and doping concentrations. The relationship between the local crystal field environment and the luminescence properties is comprehensively analyzed. Importantly, optical temperature properties of CaSrLaSbO6: Bi3+ were investigated and were found to reach a maximum relative sensitivity of 4.57 % K−1 at 298 K. Furthermore, the anti-counterfeiting ink was prepared using CaSrLaSbO6: Bi3+ phosphors, and it showed tunable emission under different light stimulation. These results indicate that CaSrLaSbO6: Bi3+ phosphors have application potential in optical temperature sensing and anti-counterfeiting.

System for control the power of an on-board signal generator of an unmanned aerial vehicle

In this paper, the issues of calibration of the transmission coeffi cient of the antenna system of a ground station for monitoring the energy characteristics of signals from global navigation satellite systems are considered. The most commonly used method for calibrating the transmission coeffi cient of large-aperture mirror antenna systems based on solar radio emission is presented, its advantages and disadvantages are described. To eliminate the disadvantages of calibration based on solar radio emission (a limited range of working angles of the site, the need to involve thirdparty data on the spectral intensity of solar radio emission), an alternative approach to calibration based on an artifi cial source of radio emission placed on board an unmanned aerial vehicle is considered. The features of this approach are indicated – the need to work in the near zone of the measured antenna system, as well as the movement of an artifi cial radio source in a plane parallel to the plane of the aperture of the antenna system. A block diagram of the payload of an unmanned aerial vehicle for measurements in the near zone of the antenna system being measured has been developed. The results of a study of the characteristics of the payload signal generator of an unmanned aerial vehicle are carried out. A solution is proposed to eliminate the error in setting the output power of the signal generator (the difference between the nominal and actual signal power) from the measurement results. The necessity of using a control signal power meter and a bandpass fi lter as part of the payload is shown. A subsystem for monitoring the output power of the signal generator has been designed. Payload components have been selected that meet the limitation on weight and size characteristics. The possibility of remotely connecting the operator to the payload equipment of an unmanned aerial vehicle has been implemented. The perspective of the development of the payload layout is described.

Negative Thermal Quenching of Photoluminescence: An Evaluation from the Macroscopic Viewpoint.

Negative thermal quenching (NTQ) denotes that the integral emission spectral intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. NTQ has been the subject of intensive investigations in recent years, and a large number of phosphors are reported to have exhibited NTQ. In this paper, a collection of results in the archival literature about NTQ of specific phosphors is discussed from a macroscopic viewpoint, focusing on the following three aspects: (1) Could the NTQ of a given phosphor be reproducible? (2) Could the associated data for a given phosphor exhibiting NTQ be in line with the law of the conservation of energy? (3) Could the NTQ of a given phosphor be demonstrated in a prototype WLED device? By analyzing typical cases based on common sense, we hope to increase awareness of the issues with papers reporting the NTQ of specific phosphors based on spectral intensity, along with the importance of maintaining stable and consistent measurement conditions in temperature-dependent spectral intensity measurement, which is a prerequisite for the validity of the measurement results.

Spectral emission characteristics of single point exposure LPBF process

Despite the advantages of laser powder bed fusion (LPBF), part defects may arise from inaccurately chosen process parameters or heat accumulation during the scanning of complex geometries. Amongst different monitored entities the chemistry or the process fingerprints related to the material requires further attention. Monitoring the spectral content of light emitted from the laser-material interaction provides insight into thermal conditions and chemical composition of the processed material. This work implements an off-axial spectral monitoring setup for Optical Emission Spectroscopy (OES) in LPBF. Single-point experiment was conducted on AISI316L and Ti-6Al-4V. The study showed that the variation of laser energy input causes consequent variation of spectral emission intensity, as well as that the developed setup successfully captures spectral peaks of alloying elements. Principal Component Analysis demonstrated clear differentiation between the two materials. These findings prove the potential of OES for monitoring alloying elements of processed material and processing conditions in LPBF.

Reduction of agglomeration effect by aluminum trihydride in solid propellant combustion

AbstractAluminum trihydride (AlH3) has gained considerable attention as a substitute fuel for aluminum in solid propellants. In this study, we conducted a systematic investigation to evaluate the effects of AlH3 content, ranging from 0 % to 18 %, on propellant ignition, combustion, and agglomeration. Experimental methods such as thermogravimetry−differential scanning calorimetry (TG‐DSC), laser ignition, high‐speed photography, and collecting condensed combustion products (CCPs) were employed. The results indicate that AlH3 significantly promotes the high‐temperature decomposition of ammonium perchlorate (AP). Meanwhile, the addition of cyclotetramethylene tetranitramine (HMX) in propellant does not affect the hydrogen release reaction of AlH3. As the AlH3 content increases from 0 % to 18 %, the spectral emission intensity of the propellants decreases, and the ignition delay time initially increases from 253 ms to 321 ms, and then decreases to 258 ms. Furthermore, the burning rate increases with increasing the AlH3 content, while the pressure exponent is reduced from 0.551 to 0.460. The inclusion of AlH3 in propellants significantly inhibits aluminum agglomeration near the burning surface. Additionally, as the AlH3 content increases, the mean particle size D43 of the CCPs decreases from 50.95 μm to 8.28 μm at 1 MPa. The agglomeration degree of aluminum is very weak at 7 MPa, especially when the AlH3 content exceeds 9 %. The conclusions drawn from this study can serve as valuable guidance for optimizing propellant formulations.

Achieving Broadband NIR Emission in Fe3+‐Activated ALaBB′O6 (A = Ba, Sr, Ca; B–B′ = Li–Te, Mg–Sb) Phosphors via Multi‐Site Ionic Co‐Substitutions

Phosphor‐converted near‐infrared (NIR) LEDs are becoming increasingly demanded as miniature, portability, and broad emission spectrum. In this work, a class of Fe3+‐activated double perovskite structured is reported ALaBB′O6 (A = Ba, Sr, Ca; B–B′ = Li–Te, Mg–Sb) phosphors. Through the co‐substitution strategy at the A‐site and B‐B' sites, the emission spectral intensity and position of Fe3+ ions can be tuned. Finally, by utilizing Ca2+ at the A‐site and Mg–Sb co‐substitution for Li–Te, long‐wave NIR emission centered at 995 nm in CaLaMgSbO6: 0.6%Fe3+ with a full width at half maximum of 147 nm and internal quantum efficiency of 54.05% is achieved. The effects of the double perovskite crystal structure on Fe3+ photoluminescence properties are comprehensively analyzed. NIR LEDs are fabricated by encapsulating UV chips with the synthetic CaLaMgSbO6: 0.6%Fe3+ phosphors, and their application value in night vision, nondestructive biological monitoring, and NIR detection is evaluated.

Study on exothermic effect of surface modified porous aluminum

Aluminum powder is widely used in the field of energy materials due to its high energy density. However, the combustion of aluminum powder is limited by the dense oxide film on the surface. In this study, surface modified porous aluminum (TFA@Al) was prepared by a simple chemical method. The morphology and structure of the TFA@Al surface were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The thermal oxidation and thermal nitridation processes of TFA@Al were analyzed by thermal analyzer (TG-DSC). The results show that the etched holes on the surface of TFA@Al can effectively promote the oxidation of aluminum and improve the exothermic effect of aluminum. The coupling reaction mechanism between Al core and oxygen at the etched holes is proposed. The explosion heat and combustion of thermite composed of TFA@Al and CuO (TFA@Al/CuO) and thermite composed of Al and CuO (Al/CuO) were also studied. The results show that TFA@Al/CuO has higher explosion heat value and emission spectral intensity than Al/CuO. Surface modified porous aluminum is expected to be used in the field of aluminum-containing energy materials.

Effect of Isopropanol on the Fluorescence of Crude Oil-in-Water Dispersions

Fluorescence spectroscopy is a promising technique to quantify crude oil-in-water because it provides information on both dissolved and dispersed molecules. One of the challenges of measuring properties of dispersions is the creaming of droplets, mainly due to density differences with the continuous phase. The addition of isopropanol to oil-in-water dispersions is an often-recommended trick to prevent the creaming of dispersed oil and obtain more reproducible measurements. Although isopropanol does not in itself fluoresce, the aim of the present work was to investigate if the emission from crude oil-in-water would be affected by the addition of isopropanol. The data set comprised synchronous fluorescence and emission spectra of 193 samples of crude oil-in-water/isopropanol mixtures, with oil concentrations varying from 10 to 1271 mg L–1 covering typical concentrations along the water treatment system offshore and isopropanol mass fractions from 0 to 1. Selected spectral features were used as input for principal component analysis, from which it was observed that the samples clustered into three groups. The isopropanol content in each mixture and, consequently, the dielectric constants were found to be the main underlying factors driving the shape and intensity of the emission bands. In the range of 0.01 to 0.5 w/w of isopropanol, the samples became milky which cleared at higher isopropanol content. Additional experiments showed that significant changes in the spectral shapes and emission intensities were observed more as a function of the isopropanol content than of the actual oil concentration. Furthermore, the quantum yield of crude oil is highly dependent on the isopropanol-to-water fraction, which means that adding isopropanol to crude oil-in-water dispersions is not advisable for oil quantification purposes by fluorescence spectroscopy.

Study of the Optical Features of Tb3+:CaYAlO4 and Tb3+/Pr3+:CaYAlO4 Crystals for Visible Laser Applications

Single crystals of Tb3+ single-doped and Tb3+/Pr3+ co-doped CaYAlO4 were produced by the Czochralski method. The room-temperature polarized absorption spectra, emission spectra, and decay curves were recorded and analyzed in detail. The absorption cross-section around 487 nm was found to be 1.53 × 10−22 cm2 for the π polarization in the Tb3+:CaYAlO4 crystal and increased to 5.23 × 10−22 cm2 in the Tb3+/Pr3+:CaYAlO4 crystal. The spectroscopic parameters were calculated through the Judd–Ofelt theory. For the Tb3+:CaYAlO4 crystal, the emission bands of green light at 546 nm and yellow light at 587 nm had fluorescence branching ratios of 64.7% and 6.65% with cross-sections of 8.82 × 10−22 cm2 (σ-polarization) and 0.44 × 10−22 cm2 (π-polarization), respectively. The decay lifetimes of 5D4 multiplets were measured to be 1.41 ms and 1.1 ms for Tb3+:CaYAlO4 and Tb3+/Pr3+:CaYAlO4 crystals, respectively. The energy transfer mechanisms of Tb3+ and Pr3+ and their emission spectral intensities at different temperatures were analyzed. As the temperature increased, the luminescence intensity of the Tb3+:CaYAlO4 and Tb3+/Pr3+:CaYAlO4 crystals decreased almost linearly with the CIE coordinate variation, from (0.370, 0.621) to (0.343, 0.636) and from (0.345, 0.638) to (0.246, 0.698), respectively. The results indicate the potential of Tb3+:CaYAlO4 and Tb3+/Pr3+:CaYAlO4 crystals as visible laser materials with a wide temperature range.

Influence of inter-pulse delay on CN molecular emission from femtosecond-nanosecond double-pulse laser-induced breakdown spectroscopy of PMMA

An experimental study on molecular emission in laser-induced breakdown spectroscopy (LIBS) was performed using an integrated femtosecond (fs) and nanosecond (ns) double-pulse (DP) laser scheme at the different inter-pulse delay between the fs and ns pulses. This work mainly included the influence of the DP inter-pulse delay on the spectral emission intensity and signal-to-background ratio (SBR). The ablated sample was polymethyl methacrylate (PMMA), and the measured molecular band was CN (Δv = 0) in the B2Σ+ − X2Σ+ transition. The results showed that the negative (ns + fs scheme) and positive (fs + ns scheme) inter-pulse delays were not much different in terms of spectral emission. The SBR excited by the fs + ns DP was higher than that excited by the ns + fs DP, and the maximum value of the SBR in the fs + ns DP-LIBS scheme was about two times that in the ns + fs DP-LIBS scheme. The higher SBR was suitable for spectral analysis, and was easy to reduce the influence of continuous emission on spectral analysis. Also, the vibration temperature of the CN molecule as a function of the inter-pulse delay between the two laser pulses was discussed. This discovery fully demonstrates that the fs + ns DP-LIBS is of great significance for detecting molecular emissions in LIBS.

Study of ignition and combustion characteristics of kerosene-based nanofluid fuel containing n-Al/CuO thermite

The ignition and combustion properties of n-Al/CuO/kerosene nanofluid fuels are examined, with a focus on the formulation effects of the n-Al/CuO nano-thermite. The DSC data shows the addition of CuO facilitates the exothermic process of n-Al particles, which then promote the n-Al/CuO/kerosene droplets to evaporate. There are two exothermic peaks on the DSC curve of n-Al/CuO (5 %) at 249.3 ℃ and 463.8 ℃, respectively. The burning of n-Al/CuO/kerosene droplets consists of four stages: ignition, d2-law combustion, vapor flame extinguishment, and agglomerate burning. During the agglomerate burning stage, n-Al/CuO (5 %)/kerosene shows the minimum ignition delay at 0.057 s and the highest emission spectral intensity. Droplet combustion conforms well to the d2-law, and the maximum combustion rate is found for n-Al/CuO (20 %)/kerosene, at 1.287 mm2 s−1. The particle size of combustion residues is uniform, and the overall appearance smoothens as the CuO content increases. A new nanofluid fuel with better ignition and combustion properties than traditional nanofluid fuels is proposed.

Thermal and fluorescence properties of Nd2O3-doped Gd2O3-Ga2O3-GeO2 glass based on the Judd-Ofelt theory

A novel type of xNd2O3-doped 14.75Gd2O3-23.33Ga2O3-(61.92-x)GeO2 glasses were successfully prepared. The thermal stability of the glass was studied by DSC and the forming ability of the glass was analyzed by XRD. Based on Judd-Ofelt theory, the strength parameters (Ω = 2, 4, 6) and radiation characteristics of the glass were analyzed detailedly by absorption and emission spectra. The results show that when the doping Nd2O3 is 1 mol%, the glasses not only have more stable thermal properties, but also have the best emission spectral intensity at 4F3/2→4I11/2 (1060 nm) with excellent radiative transition probability and stimulated emission cross section (σemis). Furthermore, it is found that the luminescence intensity of the glass ceramics obtained after heat treatment was increased by about 4.5 times due to the formation of GdGaGe2O7 crystal phase. In conclusion, the novel Nd2O3-doped Gd2O3-Ga2O3-GeO2 glass has the potential as a high power laser (1.06 μm) application material.

Luminescence properties and thermal stability of Dy3+/Eu3+co-doped single-component BaZn2(PO4)2 glass-ceramic phosphors

Highly thermally stable BaZn2(PO4)2: Dy3+/Eu3+ glass-ceramic (GC) phosphors were synthesized using a high-temperature solid-state reaction and controlled-temperature pre-crystallization method. It is found that Dy3+-doped BaZn2(PO4)2 GC phosphors produce cold white light emission at 484 nm and 575 nm under 350 nm excitation with the optimal Dy3+ doping concentration of 0.25 mol%. The theoretical analysis indicates that the dipole-dipole interaction might be the origin of the concentration quenching mechanism of phosphor. The Eu3+-doped BaZn2(PO4)2 GC phosphors produce orange-red emission at 592, 616, 654 and 700 nm under 395 nm excitation. More than that, tunable white light emission can be achieved by optimize the co-doped concentration of Eu3+ on BaZn2(PO4)2: 0.25Dy3+ GC phosphor. The emission spectral intensity and luminescence decay curves from BaZn2(PO4)2: 0.25Dy3+/yEu3+ (range of y) GC phosphors show the energy transfer from Dy3+ to Eu3+ and the emission color can be tuned from cool white to warm white region with the color correlated temperatures (CCTs) reduction from 7299 K to 2520 K. The typical BaZn2(PO4)2: 0.25Dy3+/1Eu3+ GC phosphors have a high thermal stability with an activation energy of 0.30641 eV. Finally, the white LED devices were fabricated by coupling a 363 nm UV light-emitting diode chip with the BaZn2(PO4)2: 0.25Dy3+/yEu3+ GC phosphors. These results suggest that BaZn2(PO4)2: Dy3+/Eu3+ GC phosphors may be suitable candidates for single-component white light-emitting phosphors for application in UV-WLEDs.

Experimental investigation of discharge characteristics of alternating current rotating gliding arc discharge under high air pressure

In order to study the stability of gliding arc plasma discharge under mal-conditions, an experimental system for studying the high air pressure alternating current rotating gliding arc discharge is built. The discharge characteristics, arc motion characteristics and spectral characteristics of rotating gliding arc discharge are analyzed under high pressure experimentally. Experimental results show that the voltage, current and energy increase in the gliding arc discharge with the increase of air pressure. As the air pressure rises to 0.52 MPa, the discharge energy increases from 84.74 to 147.13 J. With the increase of gas pressure, the breakdown frequency of the arc does not change monotonically, but reaches a maximum value of 26.55 kHz at 0.2 MPa, while the emission spectral intensity increases. The “arc channel mutation” occurs in the process of arc motion under high pressure. The electron excitation temperature in the process of gliding arc discharge is calculated by the two-line method, and the electron excitation temperature of gliding arc discharge is 0.8153 eV at an atmosphere pressure. The electron excitation temperature rises with the increase of air pressure. The excitation temperature increases to 5.3165 eV at an air pressure of 0.4 MPa.

Analysis of pulse-to-pulse fluctuation in underwater Laser-Induced Breakdown Spectroscopy on the basis of error propagation calculation

We study the pulse-to-pulse variation of the emission spectral intensity of underwater laser-induced breakdown spectroscopy. Emission spectral intensity and its dispersion were measured as a function of the fluence of the laser pulse at a metal target surface immersed in water. The coefficient of variation, which is an index of the dispersion, showed a minimum at a certain fluence. The dispersion at the low fluences was attributed to the variations of the population density and the atomic excitation temperature, according to the error propagation analysis of the theoretical spectral line intensity based on the Boltzmann distribution. The population density and the temperature showed a negative correlation, which is consistently explained by the unstable division of pulse energy into two parts, i.e., the early part of a pulse is attributed to materials ablation and hence to the population density, while the other part to plasma heating and hence to the temperature.

Comparison of sample temperature effect on femtosecond and nanosecond laser-induced breakdown spectroscopy

In this paper, we investigated the emission spectra of plasmas produced from femtosecond and nanosecond laser ablations at different target temperatures in air. A brass was selected as ablated target of the experiment. The results indicated that spectral emission intensity and plasma temperature showed similar trend for femtosecond and nanosecond lasers, and the two parameters were improved by increasing the sample temperature in both cases. Moreover, the temperature of nanosecond laser-excited plasma was higher compared with that of femtosecond laser-excited plasma, and the increase of the plasma temperature in the case of nanosecond laser was more evident. In addition, there was a significant difference in electron density between femtosecond and nanosecond laser-induced plasmas. The electron density for femtosecond laser decreased with increasing the target temperature, while for nanosecond laser, the electron density was almost unchanged at different sample temperatures.

Comparison of emission signals for different polarizations in femtosecond laser-induced breakdown spectroscopy

In this study, a femtosecond laser was focused to ablate brass target and generate plasma emission in air. The influence of lens to sample distance (LTSD) on spectral emission of brass plasma under linearly and circularly polarized pulses with different pulse energies was investigated. The results indicated that the position with the strongest spectral emission moved toward focusing lens with increasing the energy. At the same laser energy, the line emission under circularly polarized pulse was stronger compared with linearly polarized pulse for different LTSDs. Next, electron temperature and density of the plasma were obtained with Cu (I) lines, indicating that the electron temperature and density under circularly polarized pulse were higher compared to that under linearly polarized pulse. Therefore, changing the laser polarization is a simple and effective way to improve the spectral emission intensity of femtosecond laser-induced plasma.

Electrical and optical characterizations of a rotating gliding arc plasma-enhanced combustion dome in an aero-engine combustor

A gliding arc discharge is a typical method of producing non-equilibrium plasma, presenting excellent advantages in the field of enhanced combustion. In this study, a rotating gliding arc (RGA) plasma was combined with an aero-engine combustor dome to develop a RGA plasma-enhanced combustion dome. Experiments were conducted to investigate discharge, spectral, and infrared radiation temperature characteristics in the RGA plasma-enhanced combustion dome. Experimental results showed that two different discharge modes occurred during the RGA discharge process, the breakdown gliding mode and the steady arc gliding mode. The results had major implications for understanding the effects of the airflow rate and input voltage on the arc gliding mode transformation. The breakdown voltage, the average power, and the gliding arc rotational velocity increased with an increase in the airflow rate and a decrease of the input voltage. The spectral emission intensities of OH, O2, and O and vibrational temperature of N2 (C3Πu→B3Πg) were relatively high at a high airflow rate. Additionally, the RGA discharge had a weak temperature rise effect on electrode, which had no obvious impact on the discharge process. These characteristics could be important for future applications for controlling plasma-enhanced combustion process.

SPECTROSCOPY PECULIARITIES OF ELECTRIC ARC DISCHARGE PLASMA WITH IRON VAPOURS

This work is devoted to spectroscopy peculiarities of electric arc discharge plasma with iron vapours. The solution of the main issue of optical emission spectroscopy, namely, selection of iron spectral lines, to study the parameters of non-uniform and non-steady-state plasma source, was considered within this paper. Specifically, the Boltzmann plots technique was used for detailed analysing of application possibility of Fe I spectral lines as well as for determination of plasma temperature. The spatial profiles of selected spectral line emission intensities were used to measure the radial distributions of plasma temperature of free-burning arc discharge between consumable electrodes at 3.5 A.