Synthetic Atmosphere Research Articles

Insight into Structure, Regulatable Photoluminescence of Stably Self and Codoped Phosphor Ba3Y2B6O15: Dy/Eu for nUV wLEDs

AbstractThe exploitation of borate‐based phosphors is garnered tremendous attention in wLEDs. Although previous research provided some insights into borates from the viewpoints of synthesis, structure, and defect evolutions, their photoluminescence (PL) with dopants is still insufficient for actual application, especially on aspects of efficiency/stability. Herein, to alleviate the above issues, a new type of lesser‐known high symmetry Ba3Y2B6O15 (BYB) codoped with Dy3+/Eu3+ phosphors are synthesized via multistep solid‐state reaction and possessed controllable PL based on nUV excitation, defect‐induced (self‐) PL, and energy transfer (ET) from Dy3+ to Eu3+. The origin of blue self‐PL is clarified based on oxygen‐related defects and optimized via adjusting synthetic atmosphere (air/Ar) and (co)doping dopants to control the defect content. Thanks to dense connectivity, and highly symmetric structure with perfectly ordered octahedral sites of Y3+ for accommodation of Dy/Eu and ET, “cool” white and red PL from Dy3+ and Eu3+, respectively, show high PL efficiency with narrow full width at half the maximum (fwhm). The phosphor also exhibits excellent thermal stability because of high bandgap and low electron‐phonon coupling. Finally, a high‐quality phosphor‐converted wLED (pc‐wLED) device is assembled via remote “capping” packaging by adopting the BYB: Dy/Eu and a 350 nm nUV LED chip.

Mechanistic insights into photo-current enhancement in photo-active SrTiO3 heterojunctions under UV illumination

Photo-active heterojunctions were prepared by growing thin La0.9Sr0.1CrO3-δ films on SrTiO3 (STO) single crystals substrates via pulsed laser deposition. The photo-electrochemical characteristics of these heterojunctions under UV illumination were investigated by DC measurements and electrochemical impedance spectroscopy (EIS). Under UV illumination, the photo-current produced by these junctions increases over time by almost an order of magnitude to 1 to 2 mA cm-2 at 350 °C. Two effects governing this increase can be distinguished: A first process, independent of the surrounding atmosphere, is related to a stoichiometry polarization of the STO single crystal upon current flow. A second process is highly sensitive to contaminants in the surrounding atmosphere and is strongly accelerated in pure, synthetic atmospheres. We suggest that it is related to photo-oxidation of the STO single crystal. EIS revealed that both processes result in a decrease of both the electronic transport resistance through the STO single crystal and, to a lesser degree, the space charge resistance of the photo-active junction. Operando EIS under illumination and with DC bias was used to record the cells' photo-power characteristics and identify individual loss processes. Owing to the illumination induced strong increase of the STO single crystal conductivity, the photo-currents of such enhanced cells are limited by the space charge resistance.

Effects of Synthetic Atmosphere and Strain Rate on NO Emission from a Biogas/Hydrogen Mixture in MILD Combustion

Effects of Synthetic Atmosphere and Strain Rate on NO Emission from a Biogas/Hydrogen Mixture in MILD Combustion

Employing defect luminescence of LiGaO2 to realize dynamic readout and multiplexing of optical information

Optical data storage (ODS) materials have attracted much attention due to their unparalleled advantages, including outstanding low cost, high speed, and high storage density. The dynamic readout of high-resolution optical information in a single medium has always been a hotspot in the design of ODS materials. This work successfully developed a multi-mode dynamic luminescent material LiGaO2. By adjusting the defect states in different synthetic atmospheres, LiGaO2 materials with different luminescence properties were obtained, it appears green glow in air and nitrogen atmospheres and orange-red glow in reductive atmospheres. LiGaO2 material synthesized in a reduction atmosphere (R–LiGaO2) not only has the characteristics of rapid filling, but also has more abundant trap distribution, so it has a good optical information storage capacity, which is very suitable for the field of ODS. Through the analysis and characterization of R–LiGaO2 material in thermally-stimulated luminescence (TSL) and photostimulated luminescence (PSL), it is found that the dynamic optical information readout based on intensity-color-wavelength multiplexing in undoped single ODS materials is realized through the synergistic effect of trap centers and luminescence centers. This work provides a new strategy for the design and application of ODS materials.

Optimizing Room-Temperature Thermoelectric Performance of n-Type Bi2Te2.7Se0.3.

Bi2Te3-based compounds are exclusive commercial thermoelectric materials around room temperature. For n-type compounds, optimal thermoelectric properties are normally obtained at temperatures higher than room temperature to suppress the bipolar effect through increased carrier concentration. We find that doping with trace amounts of Cd and the addition of excess Bi are effective ways to optimize carrier concentration and achieve enhanced room-temperature thermoelectric performance for the Bi2Te2.7Se0.3 alloy in this work. For the Cd-doped samples, the replacement of Cd with Bi leads to not only a significant decrease in electron concentration but also apparently reduces the total thermal conductivity. The addition of excess Bi in the samples creates a Bi-rich synthetic atmosphere during the synthesis process, leading to increased BiTe antisite defects, decreased electron concentration, and reduced total thermal conductivity. Doping a small amount of Cd or adding excess Bi causes optimal thermoelectric performance of the n-type Bi2Te2.7Se0.3 sample shifts obviously toward low temperatures, and the samples with 0.4 atom % Cd and 0.8 atom % excess Bi achieve maximum zT of ∼0.97 at 448 K and ∼0.88 at 348 K, respectively.

Butyl-Methyl-Pyridinium Tetrafluoroborate Confined in Mesoporous Silica Xerogels: Thermal Behaviour and Matrix-Template Interaction.

Organic-inorganic silica composites have been prepared via acid catalyzed sol-gel route using tetramethoxysilan (TMOS) and methyl-trimethoxysilane (MTMS) as silica precursors and n-butyl-3-methylpyridinium tetrafluoroborate ([bmPy][BF4]) as co-solvent and pore template, by varying the content of the ionic liquid (IL). Morphology of the xerogels prepared using the ionic liquid templating agent were investigated using scanning electron microscopy and small angle neutron scattering (SANS). Thermal analysis has been used in order to evaluate the thermal and structural stability of the materials, in both nitrogen and synthetic air atmosphere. In nitrogen atmosphere, the IL decomposition took place in one step starting above 150 °C and completed in the 150–460 °C temperature interval. In synthetic air atmosphere, the IL decomposition produced two-step mass loss, mainly in the 170–430 °C temperature interval. The decomposition mechanism of the IL inside the silica matrix was studied by mass spectrometric evolved gas analysis (MSEGA). The measurements showed that the degradation of the IL’s longer side chain (butyl) starts at low temperature (above 150 °C) through a C-N bond cleavage, initiated by the nucleophilic attack of a fluorine ion.

Effects of Nitrogen/Fluorine Codoping on Photocatalytic Rutile TiO2 Crystal Studied by First-Principles Calculations.

Nitrogen/fluorine codoping of rutile TiO2 was recently reported to be effective for introducing visible-light absorption, and the resultant TiO2:N,F worked efficiently as an O2 evolution photocatalyst in a Z-scheme water-splitting system. Although an increase in the amount of nitrogen doped into rutile TiO2 lattice in the presence of fluorine was experimentally demonstrated, the role of fluorine in the system remained unclear. Here, we report a computational study on TiO2:N,F through the construction of supercell models with substitutional defects to reveal the atomic arrangement of the material and the electronic band structure. Calculations for all possible structures of nitrogen/fluorine and nitrogen/oxygen-vacancy relative positions revealed that the defect complexes were preferentially located on the (110) plane and that the distance between defects did not have a strong correlation with the formation energy. The present work also showed that although fluorine did not directly contribute to the narrowing of the band gap of TiO2:N,F, the fluorine activity of the synthetic atmosphere promotes the formation of substitutional defect complexes of nitrogen/fluorine for anion sites. This eventually increases the amount of nitrogen incorporated into the rutile TiO2 lattice and also results in reduction of the amount of oxygen vacancy, which is in qualitative agreement with our previous result of transient absorption measurement for rutile TiO2:N,F. The role of fluorine in TiO2:N,F is thus clarified through our systematic first-principles calculations.

Biosynthesis of salvinorin A

Salvia divinorum plants were exposed to a synthetic atmosphere containing 600 ppm 13CO2 for 4 hours with white light illumination and were subsequently cultured for a chase period of 10 days under standard greenhouse conditions. Salvinorin A was obtained by solvent extraction of the leaves and was purified chromatographically. The isotopolgue composition of salvinorin A was determined by NMR spectroscopy. The presence of multiply 13C-labeled isotopologues in considerable excess over their natural occurrence showed that the 13C labeling pulse had afforded multiply 13C-labeled biosynthate. Consecutive catabolic and anabolic reactions during the chase period afforded salvinorin A that was a mosaic revealing its origin from a mixture of labeled and unlabeled precursors. The presence of triple labeled isotopologues demonstrated that the IPP and DMAPP precursors of the diterpene, salvinorin A, were predominantly biosynthesized via the recently discovered non-mevalonate pathway.

Structure, valence change, and optical properties of BaMgSiO4:Eu phosphor

Optical properties of stuffed tridymite green color phosphor BaMgSiO4:Eu (BMSO:Eu) are systematic investigated in view of the structure, different synthetic atmosphere and ultraviolet (UV) stimulation. Three different Ba2+ sites are existed in equal amounts within the lattice, and considering the different ion radius between Ba2+, Mg2+, Si4+ and Eu2+/3+, dopants would be only replaced Ba2+ sites due to other sites are too small to accommodate the large Eu2+/3+. The assignments of emission bands to different Ba2+ sites are carried out according to the values of bond valence. BMSO:EuR synthesized under reducing atmosphere shows long-lasting phosphorescence (~1.2 h) while BMSO:EuA exhibits short phosphorescence (~5 min) calcined in air condition due to different concentrations of oxygen vacancies located in the vicinity of photogenerated Eu3+ cations. Photoionization of Eu2+ to Eu3+ in BMSO:EuR after UV irradiation is confirmed, and the photogenerated Eu3+ cannot change back spontaneously to Eu2+ at room temperature. The self-reduction of Eu3+ to Eu2+ is also observed for BMSO:EuAvia a substitution defect model. Altogether, the green emission of BMSO:EuA and long afterglow of BMSO:EuR indicates that this kind of phosphors have numerous potential applications, such as in white light emitting diodes (wLEDs), bioimaging and other related fields.

Development and validation of algorithms for LST measurement from NOAA-11/AVHRR satellite data

The purpose of this project was to develop the algorithms and characterise measurement errors of land surface temperature (LST). An initial investigation of the accuracy of retrieval of LST has employed synthetic radiances, produced using Lowtran7, for a series of land and atmospheric situations representative of the Australian continental climate. The synthetic data have been modelled to incorporate variation of surfaces emissivity, atmospheric temperature, water vapour profile, and the surface or boundary temperature. The study indicated that the success of the scheme depended on the validity of the modelled radiances, particularly with respect to the formulation of the radiative role of the water vapour constituent of the atmosphere. Whirls, the use of regression in deriving the coefficients for LST equation minimised the bias errors in the radiative transfer calculation that may arise from air mass dependence. However, our algorithms derived using statistical regression and synthetic atmospheres indicated good accuracy for LST measurement with and rms error of order 1°C when validated using data for an instrumented field site.

Global ECMWF Analysis Data for Estimating the Water Vapor Content Between Two LEO Satellites Through NDSA Measurements

The normalized differential spectral attenuation (NDSA) approach was proposed years ago as an effective way to estimate the integrated water vapor (IWV) along a tropospheric propagation path between two low Earth orbit satellites. Two applications are possible: the retrieval of vertical profiles of WV if the sense of rotation is opposite and the retrieval of 2-D fields of WV over vertical tropospheric sections if the sense is the same. The method relies on the measurement of the so-called spectral sensitivity $S$ at given frequencies, and on IWV-S relationships that convert $S$ into an estimate of IWV along the radio link where $S$ is measured. In this paper, we recompute the IWV-S relationships using synthetic atmospheres generated by means of European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data instead of radiosonde profiles as done by ourselves in the past. Thanks to the uniform spatial distribution of the ECMWF data on a global Earth scale, we were able to validate the IWV-S relationships in the Ku/K band previously found through synthetic atmospheres generated by means of the aforementioned irregularly spaced radiosonde data, and to define the IWV-S relationships at 179 and 181 GHz that are exploitable in the upper troposphere. Since the ECMWF data also include information about the liquid water (LW) content, we then show that an additional $S$ channel at 32 GHz can be exploited to detect and correct the bias induced by LW on IWV estimates made by applying the NDSA in the Ku/K band.

Discovery of a warm, dusty giant planet around HIP 65426

Aims. The SHINE program is a high-contrast near-infrared survey of 600 young, nearby stars aimed at searching for and characterizing new planetary systems using VLT/SPHERE’s unprecedented high-contrast and high-angular-resolution imaging capabilities. It is also intended to place statistical constraints on the rate, mass and orbital distributions of the giant planet population at large orbits as a function of the stellar host mass and age to test planet-formation theories. Methods. We used the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE to acquire high-contrast coronagraphic differential near-infrared images and spectra of the young A2 star HIP 65426. It is a member of the ~17 Myr old Lower Centaurus-Crux association. Results. At a separation of 830 mas (92 au projected) from the star, we detect a faint red companion. Multi-epoch observations confirm that it shares common proper motion with HIP 65426. Spectro-photometric measurements extracted with IFS and IRDIS between 0.95 and 2.2 μm indicate a warm, dusty atmosphere characteristic of young low-surface-gravity L5-L7 dwarfs. Hot-start evolutionary models predict a luminosity consistent with a 6–12 MJup, Teff = 1300–1600 K and R = 1.5 ± 0.1 RJup giant planet. Finally, the comparison with Exo-REM and PHOENIX BT-Settl synthetic atmosphere models gives consistent effective temperatures but with slightly higher surface gravity solutions of log (g) = 4.0–5.0 with smaller radii (1.0–1.3 RJup). Conclusions. Given its physical and spectral properties, HIP 65426 b occupies a rather unique placement in terms of age, mass, and spectral-type among the currently known imaged planets. It represents a particularly interesting case to study the presence of clouds as a function of particle size, composition, and location in the atmosphere, to search for signatures of non-equilibrium chemistry, and finally to test the theory of planet formation and evolution.

Pretreatment Effect on the Thermal Degradation of a Feedstock with Low Hemicellulose Content: Brazilian Ginseng

Pyrolysis is a well-known process for biomass upgrading, and a great deal of works are available about it. However, they focus on conventional lignocellulosic samples, and the information about any other less common samples, while still valuable, is very difficult to find. For instance, Brazilian ginseng (Pfaffia glomerata) is a feedstock without hemicellulose and a profitable source of target compounds (like beta-ecdysone) via an extraction process, also generating an exhausted solid. However, there is not much information about this biomass in the literature. For this reason, this work deals for the first time with the effect of different pretreatments on the thermal degradation behavior of Brazilian ginseng. To do so, thermogravimetric analysis (TGA) of the raw material and post-treated samples was done in a synthetic air atmosphere (20% oxygen). The thermograms were fitted via an autocatalytic model (deviation of 4.22%), and the calculated kinetics were used to analyze how the pretreatment modifies th...

Physical and chemical characteristics of Maytenus rigida in different particle sizes using SEM/EDS, TG/DTA and pyrolysis GC–MS

Thermoanalytical techniques have been widely applied in the characterization of herbal medicines, providing data about the herbal products quality. The objective of this work was to use analytical techniques for the Maytenus rigida powder in different particle sizes characterization. The techniques used were scanning electron microscopy (SEM) with energy-dispersive spectroscopy, differential thermal analysis (DTA), Thermogravimetry (TG), using the model of Ozawa to evaluate the kinetic parameters and gas chromatography coupled to pyrolysis/mass spectrometry (PYR-GC/MS). Different particle morphologies and size were verified by SEM. The thermoanalytical techniques (TG and DTA) showed physical and chemical processes occurred. Different degradation profiles curves were obtained when the samples were exposed to the atmosphere of nitrogen and synthetic air. Kinetic data showed different activation energy values and the same reaction order to the studied samples. Through Ozawa kinetic parameters, it was possible to observe granulometries distinctions to the herbal medicine powder batches. Pyrolysis allowed to correlate TG decomposition data with the identification of its degradation products and showed two similar compounds among the samples at lower temperatures (250 °C) and at higher temperatures (600 °C). The fingerprint of the degradation components by PYR-GC–MS and the other analytical tools has been utilized as an alternative to the quality control of herbal medicine evaluation. Ea obtained by dynamic TG in air synthetic atmosphere was the parameter which better differentiate the samples.

Fundamental M-dwarf parameters from high-resolution spectra using PHOENIX ACES models

M-dwarf stars are the most numerous stars in the Universe; they span a wide range in mass and are in the focus of ongoing and planned exoplanet surveys. To investigate and understand their physical nature, detailed spectral information and accurate stellar models are needed. We use a new synthetic atmosphere model generation and compare model spectra to observations. To test the model accuracy, we compared the models to four benchmark stars with atmospheric parameters for which independent information from interferometric radius measurements is available. We used $\chi^2$ -based methods to determine parameters from high-resolution spectroscopic observations. Our synthetic spectra are based on the new PHOENIX grid that uses the ACES description for the equation of state. This is a model generation expected to be especially suitable for the low-temperature atmospheres. We identified suitable spectral tracers of atmospheric parameters and determined the uncertainties in $T_{\rm eff}$, $\log{g}$, and [Fe/H] resulting from degeneracies between parameters and from shortcomings of the model atmospheres. The inherent uncertainties we find are {\sigma}$T_{\rm eff}$= 35 K, {\sigma}$\log{g}$ = 0.14, and {\sigma}[Fe/H] = 0.11. The new model spectra achieve a reliable match to our observed data; our results for $T_{\rm eff}$ and $\log{g}$ are consistent with literature values to within 1{\sigma}. However, metallicities reported from earlier photometric and spectroscopic calibrations in some cases disagree with our results by more than 3 {\sigma}. A possible explanation are systematic errors in earlier metallicity determinations that were based on insufficient descriptions of the cool atmospheres. At this point, however, we cannot definitely identify the reason for this discrepancy, but our analysis indicates that there is a large uncertainty in the accuracy of M-dwarf parameter estimates.

Herbal medicine physical quality evaluation by thermal analysis using adapted Ozawa method

The aim of this study was to evaluate the physical quality of Tabebuia caraiba (Mart.) Bur. powder, separately in three batches of different particle sizes, through the adapted Ozawa method. The Ozawa model was used for thermogravimetry (TG) data analysis in dynamic synthetic air and nitrogen atmospheres in different heating rates (5, 10, 20 and 40 °C min−1). The software TA-50 was used to data treatment. Kinetic data showed different values of activation energy and same reaction order according to the particle powder sample size in a specific model (derivative or tangent) of data treatment. The difference factor (F 1) was used to compare the parallelism line of the samples constructed by Ozawa graphs. Different kinetic results discriminate the particles size of the samples. TG technique allowed discriminating different particle sizes of herbal medicine powder.

Luminescence properties and a substitution defect model for self-reduction of europium ions in silicate Ba(Eu)MgSiO4 phosphors

The variations of luminescence properties of silicate Ba(1−x)MgSiO4:xEu phosphors are investigated in view of the structure of the host matrix and different synthetic atmosphere. X-ray powder diffraction patterns, luminescent spectra and electron spin resonance are used to confirm the compound structure and detected the simultaneous existence of both divalent and trivalent europium ions. The results indicate that both Eu2+ and Eu3+ are co-existing in the silicate when synthesized under air atmosphere due to the substitution of Eu3+cations for alkaline earth (Ba2+) triggers the formation of VBa// vacancies that play the role of electron donor towards EuBa defects. The higher the concentration of VBa//, the easier the reduction of Eu3+ into Eu2+. The co-doping with higher state chemical elements (i.e., La3+, Zr4+) helps a lot in increasing the concentration of Eu2+cations at the expense of Eu3+ ions in the Ba(1−x)MgSiO4:xEu phosphors. The energy transfer between Eu2+ cations in different sites within the BaMgSiO4 host matrix is also observed and its mechanism is charged by multipolar interaction.

Carbon-free Cu2ZnSn(S,Se)4 film prepared via a non-hydrazine route

The kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is an ideal candidate for light harvesting materials in earth-abundant low-cost thin-film solar cells (TFSC). Although the solution-based processing is a most promising approach to achieve low-cost solar cells with high power conversion efficiency, the issues of poor crystallinity and carbon residue in CZTSSe thin films are still challenging. Herein, a non-hydrazine solution-based method was reported to fabricate highly crystallized and carbon-free kesterite CZTSSe thin films. Interestingly, it was found that the synthetic atmosphere of metal organic precursors have a dramatic impact on the morphology and crystallinity of CZTSSe films. By optimizing the processing parameters, we were able to obtain a kesterite CZTSSe film composed of compact large crystal grains with trace carbon residues. Also, a viable reactive ion etching (RIE) processing with optimized etching conditions was then developed to successfully eliminate trace carbon residues on the surface of the CZTSSe film.

Effect of cooking on the thermal behavior of the cowpea bean oil (Vigna unguiculata L. Walp)

Cowpea Bean belongs to the Vigna unguiculata species and arouses interest because it has great climate adaptation and nutritional qualities. It is frequently found in the African continent and in Brazilian North and Northeast regions. It is a legume that needs to be cooked for its usual consumption. The main purpose of this study was the investigation of the lipid profile and thermal behavior of the oil from raw and cooked cowpea beans. The fatty acid composition of this oil indicates that there is a predominance of polyunsaturated fatty acids with ~37 % linoleic acid and 24 % α-linolenic acid, against ~25 % of saturated fatty acids (mostly palmitic). Details concerning the thermal behavior of these oils were evaluated by thermogravimetry and differential scanning calorimetry (DSC), under nitrogen and synthetic air atmospheres. The kinetic parameters were evaluated from several heating rates with sample mass of 5 and 20 mg in open crucibles under synthetic air and nitrogen atmospheres. The obtained data were evaluated with the iso-conversional kinetic method, where the values of activation energy (E a/kJ mol−1) were evaluated in function of the conversion degree (a). The results indicate that the kinetic behavior of the cooked oil under nitrogen and synthetic air atmospheres are different, which was attributed to the several sample masses used. In addition, this oil also was evaluated by DSC from 25 to −60 °C, where it was verified a phase transition behavior.

Evaluation of the Thermic Behavior of the Coal as a Byproduct through the Low Temperature Conversion Process – LTC of the Sewage Sludge

Brazil follows the global trend to seek viable alternative energy sources that can improve the quality and secure supply of energy with environmental sustainability, allied to the necessity of facilitating a fitting end to the sludge treatment plants sewage. The biomass present in SS is emerging as an alternative to the country's energy matrix, through the Low Temperature Conversion process – LTC of the sludge in the production of biofuel (biooil and coal). This article aims to characterize the coal obtained through the Low Temperature Conversion and evaluate the thermal behavior. In this study physical and chemical studies were made: elemental analysis (CHNO), calorific power, Thermogravimetry (TG) at a heating rate of 10°C min-1 under synthetic air atmosphere, and spectroscopic. The thermogravimetric study found a thermal stability at 300oC. In the spectroscopy in the infrared (IR) regionit was observed bands related to the presence of water, organic matter and silicon oxides in the SS samples analyzed.