Characteristic Emission Spectra Research Articles

Molecular laser-induced breakdown spectroscopy for elemental analysis

Abstract Laser-induced breakdown spectroscopy (LIBS) with pulsed laser excitation is a well-established method for analyzing the atomic components of an unknown sample based on their characteristic emission spectra. However, standard LIBS analysis provides insufficient results if the atoms to be measured exhibit weak elemental emission lines or if characteristic elemental spectra are disturbed by overlapping stronger lines of other elements in the sample. The analysis of the molecular emission bands arising in the plasma cooling phase seems to be a promising solution. The analysis is carried out by the observation of newly formed radicals and diatomic molecules whose strong molecular emission bands can often be found in the visible spectral region and offer a higher detection sensitivity. This generally requires a time resolved measurement of the LIBS spectra, but we show that in some cases this is not necessarily needed. As an application we present the measurement of chloride contamination in concrete that could help to estimate the repair demand of infrastructure buildings in future.

Detailed characterization of a highly Yb-doped double-clad fiber

A characterization method based on the careful measurement of the characteristic parameters and fluorescence emission spectra of a highly Yb-doped double-clad fiber is presented. The method is successfully checked by numerically fitting experimental results of a ring laser based on highly doped double-clad Yb-doped silica fibers with different dopant concentrations, fiber lengths and ring-laser output-coupler rates.

In-Field, In Situ, and In Vivo 3-Dimensional Elemental Mapping for Plant Tissue and Soil Analysis Using Laser-Induced Breakdown Spectroscopy.

Sensing and mapping element distributions in plant tissues and its growth environment has great significance for understanding the uptake, transport, and accumulation of nutrients and harmful elements in plants, as well as for understanding interactions between plants and the environment. In this study, we developed a 3-dimensional elemental mapping system based on laser-induced breakdown spectroscopy that can be deployed in- field to directly measure the distribution of multiple elements in living plants as well as in the soil. Mapping is performed by a fast scanning laser, which ablates a micro volume of a sample to form a plasma. The presence and concentration of specific elements are calculated using the atomic, ionic, and molecular spectral characteristics of the plasma emission spectra. Furthermore, we mapped the pesticide residues in maize leaves after spraying to demonstrate the capacity of this method for trace elemental mapping. We also used the system to quantitatively detect the element concentrations in soil, which can be used to further understand the element transport between plants and soil. We demonstrate that this method has great potential for elemental mapping in plant tissues and soil with the advantages of 3-dimensional and multi-elemental mapping, in situ and in vivo measurement, flexible use, and low cost.

Intravital multiphoton photoconversion with a cell membrane dye.

Photoconversion, an irreversible shift in a fluorophore emission spectrum after light exposure, is a powerful tool for marking cellular and subcellular compartments and tracking their dynamics in vivo. This paper reports on the photoconversion properties of Di-8-ANEPPS, a commercially available membrane dye. When illuminated with near-infrared femtosecond laser pulses, Di-8-ANEPPS undergoes multiphoton photoconversion as indicated by the supralinear dependence of the conversion rate ρpc on the incident power (ρpc∝Iexc2.27), and by the ability to photoconvert a thin optical section in a three-dimensional matrix. The characteristic emission spectrum changed from red to blue, and ratiometric analysis on single cells in vitro revealed a 65-fold increase in the blue to red wavelength ratio after photoconversion. The spectral shift is preserved in vivo for hours, making Di-8-ANEPPS a useful dye for intravital cell marking and tracking applications.

Dy3+‐, Sm3+‐, Ce3+‐ and Tb3+‐activated optical properties of microcrystalline BaMgP2O7 phosphors

Photoluminescence (PL) and thermoluminescence (TL) properties of rare earth (RE) ion (RE=Dy3+ , Sm3+ , Ce3+ , Tb3+ ) activated microcrystalline BaMgP2 O7 phosphors are presented in this work. Non-doped and doped samples of BaMgP2 O7 were prepared using a solid state diffusion method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), PL and TL. The XRD measurement confirmed the phase purity of the BaMgP2 O7 host matrix. The average particle size was found through SEM measurement to be around 2μm. All activators using the PL technique displayed characteristic excitation and emission spectra that corresponded to their typical f→f and f→d transitions respectively. Thermoluminescence measurements showed that BaMgP2 O7 :RE (RE=Dy3+ , Sm3+ , Tb3+ , Ce3+ ) and co-doped BaMgP2 O7 :Ce3+ ,Tb3+ phosphors have also TL behaviour.

Europium‐activated rare earth fluoride (LnF3:Eu3+–Ln = La, Gd) nanocrystals prepared by using ionic liquid/NH4F as a fluorine source via hydrothermal synthesis

AbstractLanthanide (Ln) fluorides are considered exceptional luminescent rigid host matrices for various optical active Ln3+ ions due to their high refractive index, high chemical stability and low phonon energy, leading to the low probability of non‐radiative decay, which results in higher photoluminescence quantum yield (PLQY) (usually higher than oxide hosts). In this study, Eu3+‐activated Ln fluorides (LnF3:Eu3+–Ln = La, Gd) are synthesized by the hydrothermal method using 1‐butyl‐3‐methylimidazolium tertrafluoroborate [BMIBF4] and NH4F as fluorine precursors. The synthesized nanocrystals (NCs) are structurally and morphologically characterized, and their optical properties investigated using spectrofluorometry. The X‐ray diffraction (XRD) patterns of Eu3+‐substituted and ‐unsubstituted LnF3 (prepared from a different fluorine source) are indexed based on the hexagonal and orthorhombic crystal structure, respectively. Average crystalline sizes are calculated using the Scherrer equation and it is found that the synthesized NCs have an average crystalline size of 12–35 nm. Transmission electron microscopy (TEM) images reveal that the NCs are well dispersed and nearly ellipsoid, with an average size of ~ 5 nm. Eu3+‐activated NCs show characteristic excitation and emission spectra. The emission spectra show both magnetic (5D0–7F1) and electric (5D0–7F2) dipole transition with appropriate CIE color coordinates; however, the intensity of the magnetic dipole transition is high, which is in accordance with local site symmetry. Owing to their unique size and excellent optical properties, the synthesized NCs may have potential application in the fields bio‐imaging and solar concentrators. Copyright © 2016 John Wiley & Sons, Ltd.

Electric and plasma characteristics of RF discharge plasma actuation under varying pressures**Project supported by the National Natural Science Foundation of China (Grant Nos. 11472306, 51336011, and 51407197).

The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been investigated experimentally. As the pressure increases, the shapes of charge–voltage Lissajous curves vary, and the discharge energy increases. The emission spectra show significant difference as the pressure varies. When the pressure is 1000 Pa, the electron temperature is estimated to be 4.139 eV, the electron density and the vibrational temperature of plasma are 4.71×1011 cm−3 and 1.27 eV, respectively. The ratio of spectral lines which describes the electron temperature hardly changes when the pressure varies between 5000–30000 Pa, while it increases remarkably with the pressure below 5000 Pa, indicating a transition from filamentary discharge to glow discharge. The characteristics of emission spectrum are obviously influenced by the loading power. With more loading power, both of the illumination and emission spectrum intensity increase at 10000 Pa. The pin–pin electrode RF discharge is arc-like at power higher than 33 W, which results in a macroscopic air temperature increase.

Characteristics of the spontaneous emission field and spectrum of a two-level atom in a dynamic photonic crystal

The spontaneous emission field and spectrum of a two-level atom, located in an isotropic photonic crystal with dynamic band edges, are investigated by means of numeric calculation. The investigation is expected to help comprehend the characteristics of the atomic spontaneous emission in the dynamic photonic crystal, and provide a possible way to control dynamically the spontaneous emission in photonic crystal. The expression of the spontaneous radiation field is obtained without using the far-zone approximation and the Weisskopf-Wigner approximation, and expected to be applicable in other relevant researches. In the investigation, the spontaneous radiation field and spectrum are calculated when the band edge frequency is unmodulated, or modulated by a step function or triangle function. In the unmodulated situation, the radiation field intensity tends to a constant which is equal to the intensity of the localized field component. The radiation field pulse presents a wave packet behavior as propagation distance increases. The components of the radiation field correspond one-to-one to the peaks in the spontaneous radiation spectrum. When the band edge frequency is modulated by step function, the radiation field intensity tends to a steady-state value after the modulation has happened. And the steady-state intensity is affected by the time when the modulation happens. The components of the non-localized field and the frequency of the localized field after modulation depend on the atomic transition frequency and the band edge frequency, and are identical to those in the unmodulated situation with the same parameters. When the band edge frequency is modulated by a triangle function, the field intensity presents a decaying quasi-periodic oscillation after a long enough time. The modulation frequency determines the frequency of the oscillation, and influences the decay rate. The radiation energy becomes sharp peaks around a set of the discrete frequencies which are evenly spaced with the modulation frequency. The central frequency of these frequencies depends on the atomic transition frequency and the value range of the band edge frequency. The modulation initial phase affects the intensity of the radiation field emitted in an initial period of time.

Photoluminescence study of rare earth doped Yttrium aluminum garnet—YAG:RE (RE: Eu3+, Pr3+ and Tb3+)

Yttrium aluminum garnet (YAG) phosphor powders doped with rare earth ions (Eu3+, Pr3+and Tb3+) were synthesized by mixed fuel combustion method at low temperature. The XRD analysis of the powders confirms the formation of pure phase of YAG even at low temperature. A systematic study of the fluorescence properties of YAG:Eu3+, YAG:Pr3+ and YAG:Tb3+ shows respective characteristics excitation and emission spectra confirms the incorporation of ions in YAG.

Characterisation of estuarine intertidal macroalgae by laser-induced fluorescence

The article reports the application of laser-induced fluorescence (LIF) for the assessment of macroalgae communities of estuarine intertidal areas. The method was applied for the characterisation of fifteen intertidal macroalgae species of the Tagus estuary, Portugal, and adjacent coastal area. Three bands characterised the LIF spectra of red macroalgae with emission maxima in the ranges 577–583 nm, 621–642 nm and 705–731 nm. Green and brown macroalgae showed one emission maximum in the red region (687–690 nm) and/or one in the far-red region (726–732 nm). Characteristics of LIF emission spectra were determined by differences in the main fluorescing pigments: phycoerythrin, phycocyanin and chlorophyll a (Chl a). In the green and brown macroalgae groups, the relative significance of the two emission maxima seems to be related to the thickness of the photosynthetic layer. In thick macroalgae, like Codium tomentosum or Fucus vesiculosus, the contribution of the far-red emission fluorescence peak was more significant, most probably due to re-absorption of the emitted red Chl a fluorescence within the dense photosynthetic layer. Similarly, an increase in the number of layers of the thin-blade green macroalgae Ulva rigida caused a shift to longer wavelengths of the red emission maximum and the development of a fluorescence peak at the far-red region. Water loss from Ulva's algal tissue also led to a decrease in the red/far-red Chl fluorescence ratio (F685/F735), indicating an increase in the density of chloroplasts in the shrinking macroalgal tissue during low tide exposure.

Photoluminescence of Sm3+ doped ZrO2 coatings formed by plasma electrolytic oxidation of zirconium

In this paper, we have investigated photoluminescence (PL) of Sm3+ doped ZrO2 coatings formed by plasma electrolytic oxidation (PEO) of zirconium in electrolyte containing Sm2O3 powder. Obtained PL emission spectra feature two distinct regions. The first region is related to ZrO2 PL band with maximum positioned at about 490nm, while the second region in the orange-red part of the spectrum shows four sharp emission bands which are related to f–f transitions of Sm3+ from excited level 4G5/2 to the lover levels 6HJ (J=5/2, 7/2, 9/2, and 11/2). Increase of PL with time is related to increase of oxygen vacancy defects and the content of Sm3+ in the coatings formed during the process.

Improving the efficiency of emission extraction from nitride LED structures with textured interfaces

The light-emitting diode (LED) structures based on gallium nitride (GaN) and grown on sapphire substrates were investigated. The obtained experimental data include the emission spectrum, optical power and current-voltage characteristics. Monte Carlo simulation based on the parameters of the structures was conducted. During the simulation optimal parameters of surface texturing were evaluated, and alternative methods of structure modification were shown.

Synthesis and cathodoluminescent properties of Lu3(Al,Ga)5O12:Tb3+ with and without niobium-doped TiO2 coating

(Lu0.95Tb0.05)3(Al0.80Ga0.20)5O12 (LuAGG:Tb) phosphor is synthesized by a high-temperature solid-state reaction, and a thin layer of niobium-doped TiO2 (NTO) is deposited on the phosphor particles by coprecipitation-assisted solvothermal synthesis. The crystal structure, micromorphology, chemical bonding, and cathodoluminescent (CL) properties of both the uncoated and NTO-coated phosphors are determined. The phosphor powders possess a single phase, and the average diameter of the particles is about 3 μm. NTO nanoparticles with the anatase crystal structure are connected to the phosphor particles electrostatically. Both types of phosphors exhibit the characteristic emission spectrum of Tb3+ under electron excitation. The CL intensity decreases, whereas the resistance to luminance saturation and degradation increases with the coating.

Physically-based in silico light sheet microscopy for visualizing fluorescent brain models.

BackgroundWe present a physically-based computational model of the light sheet fluorescence microscope (LSFM). Based on Monte Carlo ray tracing and geometric optics, our method simulates the operational aspects and image formation process of the LSFM. This simulated, in silico LSFM creates synthetic images of digital fluorescent specimens that can resemble those generated by a real LSFM, as opposed to established visualization methods producing visually-plausible images. We also propose an accurate fluorescence rendering model which takes into account the intrinsic characteristics of fluorescent dyes to simulate the light interaction with fluorescent biological specimen.ResultsWe demonstrate first results of our visualization pipeline to a simplified brain tissue model reconstructed from the somatosensory cortex of a young rat. The modeling aspects of the LSFM units are qualitatively analysed, and the results of the fluorescence model were quantitatively validated against the fluorescence brightness equation and characteristic emission spectra of different fluorescent dyes.AMS subject classificationModelling and simulation

Assessing Spatial Resolution of Cathodo-Luminescence Imaging and Spectroscopy at the Nanoscale for Inorganic Phosphor Powders

It is now possible to easily collect CL images (using a photomultiplier tube using total or filtered light) and emission spectra from individual nanometer sized particles using the commercially available Gatan Vulcan attachment for a transmission electron microscope (TEM). In our case, at Brunel University London, we have fitted this to a JEOL 2100F field emission TEM. This work demonstrates the spatial resolution that has been achieved when imaging various phosphor nano materials and discusses the limitations of the technique. It also demonstrates the uniformity of excitation/emission from various phosphors, and hence the effectiveness of the synthetic method used to manufacture the phosphor can be seen. Conventionally, photoluminescence (PL) and cathodoluminescence (CL) spectra are collected from bulk phosphor samples and are the average of all of the particles in the sample. This is true of most samples made either in the laboratory for research or commercial materials prepared by industrial companies. Cathodoluminescence spectra have been collected from nanometer-sized crystals of quantum dots (spherical and rods) and various oxide and oxysulfide phosphors. The latter phosphors have been implemented into CL applications on a vast scale whereas the quantum dot materials are not designed for CL application and therefore great care is required when imaging these materials to minimize the effect of beam damage. When observing mixtures of phosphors (Gd2O2S:Tb3+ and Y2O3:Eu3+) it is apparent that when the electron beam is positioned onto one of these two materials and the spectrum observed, then the other phosphor emission spectrum can be observed if the particles are nearby. However when observing quantum dot materials the spatial resolution is only limited by the particle size. A tentative explanation for this effect is given. In this work we compare the spectra of nanometer sized phosphor crystals/particles in order to understand any variation in the emission spectra between the phosphor grains and to understand the effect of temperature on their luminescent properties. Our results will be presented that could only have been found by using CL spectra obtained directly from single nanoparticles. In conclusion: 1) The effect of different TEM machine parameters will be discussed 2) The CL spatial resolution will be demonstrated Figure 1. Left) HAADF STEM of nanometre-sized single crystals of Y2O3Eu3+ and Gd2O2S:Tb3+; The green line spectrum image shows where 10 emission spectra were recorded at equally spaced intervals. Right) Extracted spectra taken from opposite ends on the line scan show the characteristic CL emission spectrum for both the Eu3+ and Tb3+ are observed in both spectra. Figure 1

Synthesis and Luminescence of Y2O3:Eu3+ Nanoparticles by the Coprecipitation

The Y2O3:Eu3+ nano-phosphors were synthesized by coprecipitation with the addition of oleic acid. The XRD pattern and TEM images show that the obtained Y2O3:Eu3+ samples are spherical nanoparticles with the body centered cubic structure. Upon excitation into the CTB of Eu3+ ions at 266 nm, Y2O3:Eu3+ samples show the characteristic emission spectra of Eu3+ ions originating from the 5D0 → 7Fj transitions. The corresponding luminescence decay times can be fitted well with a single exponential decay curve. The emission intensity increases with the increase of Eu3+ doped concentration, but the luminescence lifetime is just opposite to it.

A novel image-guided FT-IR sensor using chalcogenide glass optical fibers for the detection of combustion gases

An optical-fiber-based sensor suitable for the detection of combustion gases was designed and experimentally implemented with state-of-the-art sensitivity and capabilities. The system can not only provide imaging capability, but also provide spectral capability of the field of view (FOV) center guided by the imaging. The sensor employs a Fourier transform infrared (FT-IR) spectrometer, coupled with chalcogenide glass optical fiber, and a specially designed infrared optic lens. A special kit provided by Bruker Optics is connected on the spectrometer to focus the infrared beam from the lens at the entry of the fiber. It was tested in situ, in real time, under real-world conditions. Since each gas shows a characteristic optical emission spectrum, it is possible to detect selectively and quantitatively the presence of gases in combustion environment by analyzing mid-IR spectra. Spectral investigation techniques based on spectral shape band intensities and areas are tested to find the most effective tool for monitoring combustion gases. A comparison with experimental data has demonstrated that this sensor is well designed to study gases coming from combustion processes.

케로신/공기 와류 화염의 화학발광 세기 특성에 관한 실험적 연구

The present study presents experimental results on the characteristics of emission spectra of kerosene/air swirl flames. The aviation fuel Jet A-1, which is used for the liquid rocket engines of the Korea Space Launch Vehicle, is used with three different swirlers to investigate the swirl strength effects. The emission spectra from the flames are measured with a spectrometer as the swirl strength and combustion air temperature are varied. Chemiluminescence intensities of , and are identified from the spectra. The chemiluminescence intensities from the kerosene flames show sensitivity to the swirl strength and are affected by changes in the combustion air temperature. Among the three radicals of interest, show the most significant changes in chemiluminescence intensity with the swirl strength and equivalence ratio. The intensity ratios and are adequate for indicating changes in the equivalence ratio with the air and fuel mass flow rates, respectively.

Photooxidation and Photoluminescence of Triarylmethane Dye-Conjugated Zinc Complexes: Optical Anisotropy and Optical Activity Emerging from Distinct Crystal Packing Modes

Abstract A series of hexanuclear zinc complexes was prepared using a triarylmethane (TAM)-based ligand. Depending on the alkyl chains at the peripheral position of the complex, the complexes crystallized as needles, octahedral crystals, or both. A needle crystal consisting of molecular columns in which P- and M-forms of propeller-shaped complexes were alternately stacked. Octahedral crystals had an enantiomeric cubic system. All crystals were photooxidized under UV irradiation to yield the corresponding TAM dyes with characteristic absorption (ca. 540 nm) and emission (ca. 600 nm) spectra. The crystals with the columnar packing structure exhibited linearly polarized emission, while the crystals with the cubic system did not show noticeable dichroism in either absorption or emission. The differences in photophysical properties among the complexes with various alkanoic groups were interpreted in terms of the spatial arrangement of the TAM dye molecules in the crystals.

Caging metal ions with visible light-responsive nanopolymersomes.

Polymersomes are bilayer vesicles that self-assemble from amphiphilic diblock copolymers, and provide an attractive system for the delivery of biological and nonbiological molecules due to their environmental compatibility, mechanical stability, synthetic tunability, large aqueous core, and hyperthick hydrophobic membrane. Herein, we report a nanoscale photoresponsive polymersome system featuring a meso-to-meso ethyne-bridged bis[(porphinato)zinc] (PZn2) fluorophore hydrophobic membrane solute and dextran in the aqueous core. Upon 488 nm irradiation in solution or in microinjected zebrafish embryos, the polymersomes underwent deformation, as monitored by a characteristic red-shifted PZn2 emission spectrum and confirmed by cryo-TEM. The versatility of this system was demonstrated through the encapsulation and photorelease of a fluorophore (FITC), as well as two different metal ions, Zn2+ and Ca2+.