Distinct Emission Patterns Research Articles

Binary and heterostructured microplates of iridium and ruthenium complexes: Preparation, characterization, and thermo-responsive emission

Thermo-responsive microcrystals exhibiting obvious emission intensity or color changes have great potentials in sensing, information encryption, and microelectronics. We report herein the binary assembly of a blue-emissive iridium complex and a red-emissive ruthenium complex into homogeneously-doped or optically-heterostructured microcrystals with thermo-responsive properties. Depending on the assembly conditions, lateral or longitudinal triblock heterostructures with a microplate shape are obtained, which display distinct emission pattern changes upon heating as a result of the decreased efficiency of energy transfer. In addition, branched heterostructures are prepared by a stepwise assembly. The luminescence polarization of the homogeneously-doped binary crystals and the waveguiding property of the longitudinal triblock heterostructure are further examined. This work evidences the versatility of transition metal complexes in the assembly into various luminescent nano/micro structures with potential applications in thermo-sensing and nanophotonics.

Tunable emission color of novel Y3NbO7:xDy3+ phosphor

Powders of Y3NbO7:xDy3+ (x = 0.5, 1, 1.5, 3 and 5 mol%) were produced through a solid-state process. X-ray diffraction investigations confirm the fluorite-type structure (space group 𝐹𝑚3̅𝑚) of powders with crystallite size in the range of 19–60 nm. Both the photoluminescence excitation and emission spectra revealed the presence of defects within the material. With different excitation wavelengths, the emission spectra exhibited distinct emission patterns. At each excitation wavelength, the emission was quenched at Dy3+ concentration higher than 1 mol%. The decay time measurements of the highest intensity emission revealed a progressive decrease from 0.472 milliseconds for x = 0.5 mol% to 0.246 milliseconds for x = 5 mol%. The CIE chromaticity coordinates investigation revealed that the emission color may be altered by varying the excitation wavelength, ranging from blue (excitation at 333 nm) and near-white (excitation at 353 nm and 390 nm) to orange (excitation at 457 nm). The chromaticity of emission under 353 nm and 390 nm excitation validated the material's suitability as an almost-white phosphor.

A new multiregional carbon emissions forecasting model based on a multivariable information fusion mechanism and hybrid spatiotemporal graph convolution network

Developing scientific and effective carbon emissions reduction policies relies heavily on precise carbon emission trend prediction. The existing complex spatiotemporal correlation and diverse range of influencing factors associated with multi-regional carbon emissions pose significant challenges to accurately modeling these trends. Under this constraint, this study is inspired by graph learning to establish a hybrid dynamic and static graph-based regional carbon emission network framework, which introduces a novel research standpoint for investigating short-term carbon emissions prediction (CEP). Specifically, a parallel framework of attribute-augmented dynamic multi-modal graph convolutional neural networks (ADMGCN) and temporal convolutional networks with adaptive fusion multi-scale receptive fields (AFMRFTCN) is proposed. The proposed model is evaluated against nineteen state-of-the-art models using daily carbon emission data from 30 regions in China, demonstrating its effectiveness in accurately predicting the trends of multi-regional carbon emissions. Conclusions are drawn as follows: First, especially in regions with marked periodicity, compared with the best baseline model, the mean absolute percentage error (MAPE) of our model is reduced by 20.19%. Second, incorporating graph convolutional neural networks (GCNs) with dynamic and static graphs is advantageous in extracting the spatial features of China's carbon emission network, which are influenced by geographical, economic, and industrial factors. Third, the parallel ADMGCN-AFMRFTCNs framework effectively captures the influence of external information on carbon emissions while mitigating the issue of low prediction accuracy resulting from univariate information. Fourth, the analysis reveals significant differences in the short-term (30-day) growth rate of carbon emissions among different regions. For example, Henan exhibits the highest growth rate (37.38%), while Guizhou has the lowest growth rate (−7.46%). It is valuable for policymakers and stakeholders seeking to identify regions with distinct emission patterns and prioritize mitigation efforts accordingly.

Orbital- and Spin-phase Variability in the X-Ray Emission from the Accreting Pulsar Centaurus X-3

We present a time-resolved analysis using 39 ks NuSTAR observation data of the X-ray pulsar Centaurus X-3, covering an orbital-phase interval of Φ = 0.199–0.414. The orbital- and spin-phase variabilities are investigated through time-resolved spectra, light curves, and pulse profiles. The orbital-phase variability was due to the mixture of two comparable effects: intrinsic flux variability of ∼10% and obscuration by the clumpy stellar wind. The typical size and number density of the clumps are ∼9 × 1010 cm and ∼3 × 1012 cm−3, respectively. In the spin-phase-resolved analysis, we detected variations in the spectral features of the continuum, the Fe line, and the cyclotron resonance scattering feature (CRSF). The photon index ranged from 0.72 to 1.06, corresponding to the difference in the Comptonization optical depth by a factor of ∼1.6. The equivalent width and intensity of the Fe line had negative correlations with the continuum flux. The central energy and the strength of the CRSF increased at the pulse maximum. The former ranged from 26.0 to 28.7 keV, while the latter varied by a factor of ∼1.9. The pulse profile was double-peaked in the low-energy band, and it gradually shifted to being single-peaked with energy, indicating the existence of two distinct emission patterns, corresponding to the pencil and fan beams. Finally, we found that the pulse profiles were highly stable along the orbital phase, within a variation degree of ∼20%, which provides evidence of the highly stable accretion stream of the binary system.

An assessment of emission characteristics of Northern Hemisphere cities using spaceborne observations of CO2, CO, and NO2

Intensified anthropogenic activities and high levels of energy consumption in cities have led to an increase in emissions of CO2 and air pollutants, impacting air quality and calling for better measures to monitor and reduce emissions. This study assesses the emission characteristics of cities in the Northern Hemisphere during two winter seasons from December 2018 to March 2020 using a combination of CO2 observations from the Orbiting Carbon Observatory-2 (OCO-2) along with CO and NO2 observations from the Sentinel-5 Precursor TROPOspheric Monitoring Instrument (S-5P TROPOMI). We calculate the estimates of urban enhancement concentrations of CO2, CO, and NO2 from anthropogenic emissions in cities. Moreover, using ratios of CO/CO2 and NO2/CO2 according to each city, we analyze the relationship between CO2 and air pollutants and find that cities show distinct emission patterns according to where they are located in different regions of the world. Our analysis shows that a positive relationship exists in the comparisons of CO/CO2 and NO2/CO2 ratios to city population and GDP. However, when cities in the Northern Hemisphere are divided into “developed” and “developing” regions, a difference in pattern is found where most developed cities show a smaller increase of both CO/CO2 and NO2/CO2 ratios with the increase of GDP, while developing cities show a larger increase of ratios per increase of GDP. Especially, developing cities facing rapid economic development like Mumbai and Tianjin show high emission ratios that almost match that of developed cities. The higher incline of increase in emission ratios in developing cities can be attributed to the low combustion efficiency of fossil fuels along with less stringent pollution control measures. This implies that pollution control measures are crucial for effective management of air quality degradation with economic advancement within these developing cities. The analysis also highlights the importance of urban geological features in cities such as that of Tehran and Milan which can trap air pollution under appropriate meteorological conditions. Despite the short period of analysis, our study demonstrates that satellite observations of CO2 and air pollutants together can provide clues about factors controlling the co-emission of air pollutants and carbon in cities and suggests that the application of the proposed methods with longer periods of observation will support coupled air quality and climate mitigation strategies.

Signatures of an atomic crystal in the band structure of a C60 thin film

Transport phenomena in molecular materials are intrinsically linked to the orbital character and the degree of localization of the valence states. Here, we combine angle-resolved photoemission with photoemission tomography to determine the spatial distribution of all molecular states of the valence band structure of a C$_{60}$ thin film. While the two most frontier valence states exhibit a strong band dispersion, the states at larger binding energies are characterized by distinct emission patterns in energy and momentum space. Our findings demonstrate the formation of an atomic crystal-like band structure in a molecular solid with delocalized $\pi$-like valence states and strongly localized $\sigma$-states at larger binding energies.

Dual-radiotracer translational SPECT neuroimaging. Comparison of three methods for the simultaneous brain imaging of D2/3 and 5-HT2A receptors

PurposeSPECT imaging with two radiotracers at the same time is feasible if two different radioisotopes are employed, given their distinct energy emission spectra. In the case of 123I and 125I, dual SPECT imaging is not straightforward: 123I emits photons at a principal energy emission spectrum of 143.1–179.9 keV. However, it also emits at a secondary energy spectrum (15–45 keV) that overlaps with the one of 125I and the resulting cross-talk of emissions impedes the accurate quantification of 125I. In this paper, we describe three different methods for the correction of this cross-talk and the simultaneous in vivo [123I]IBZM and [125I]R91150 imaging of D2/3 and 5-HT2A receptors in the rat brain. MethodsThree methods were evaluated for the correction of the effect of cross-talk in a series of simultaneous, [123I]IBZM and [125I]R91150 in vivo and phantom SPECT scans. Method 1 employs a dual-energy window (DEW) approach, in which the cross-talk on 125I is considered a stable fraction of the energy emitted from 123I at the principal emission spectrum. The coefficient describing the relationship between the emission of 123I at the principal and the secondary spectrum was estimated from a series of single-radiotracer [123I]IBZM SPECT studies. In Method 2, spectral factor analysis (FA) is applied to separate the radioactivity from 123I and 125I on the basis of their distinct emission patterns across the energy spectrum. Method 3 uses a modified simplified reference tissue model (SRTMC) to describe the kinetics of [125I]R91150. It includes the coefficient describing the cross-talk on 125I from 123I in the model parameters. The results of the correction of cross-talk on [125I]R91150 binding potential (BPND) with each of the three methods, using cerebellum as the reference region, were validated against the results of a series of single-radiotracer [123I]R91150 SPECT studies. In addition, the DEW approach (Method 1), considered to be the most straightforward to apply of the three, was further applied in a dual-radiotracer SPECT study of the relationship between D2/3 and 5-HT2A receptor binding in the striatum, both at the voxel and at the regional level. ResultsAverage regional BPND values of [125I]R91150, estimated on the cross-talk corrected dual-radiotracer SPECT studies provided satisfactory correlations with the BPND values for [123I]R91150 from single-radiotracer studies: r = 0.92, p < 0.001 for Method 1, r = 0.92, p < 0.001 for Method 2, r = 0.92, p < 0.001, for Method 3. The coefficient describing the ratio of the 123I-emitted radioactivity at the 125I-emission spectrum to the radioactivity that it emits at its principal emission spectrum was 0.34 in vivo. Dual-radiotracer in vivo SPECT studies corrected with Method 1 demonstrated a positive correlation between D2/3 and 5-HT2A receptor binding in the rat nucleus accumbens at the voxel level. At the VOI-level, a positive correlation was confirmed in the same region (r = 0.78, p < 0.01). ConclusionDual-radiotracer SPECT imaging using 123I and 125I-labeled radiotracers is feasible if the cross-talk of 123I on the 125I emission spectrum is properly corrected. The most straightforward approach is Method 1, in which a fraction (34%) of the radioactivity emitted from 123I at its principal energy spectrum is subtracted from the measured radioactivity at the spectrum of 125I. With this method, a positive correlation between the binding of [123I]IBZM and [125I]R91150 was demonstrated in the rat nucleus accumbens. This result highlights the interest of dual-radiotracer SPECT imaging to study multiple neurotransmitter systems at the same time and under the same biological conditions.

Dietary emissions patterns and their effect on the overall climatic impact of food consumption

SummaryFood consumption is responsible for a considerable proportion of greenhouse gas emissions (GHGE). This study aimed to determine whether different dietary emission patterns (EPs) are evident in the Irish population. Respondents of the national nutritional survey were segmented using cluster analysis based on GHGE generated from food groups; thereby profiling similarities in how emissions were attained. Three distinct EPs were observed: Unsustainable, Culturally Sustainable, and Nutritionally Sustainable. The Unsustainable pattern had a significantly greater climatic impact; generating significantly higher emissions from processed meat, alcohol, carbonated beverages and savoury snacks, but significantly lower emissions from dairy.Total GHGE did not differ significantly between the Culturally Sustainable and the Nutritionally Sustainable despite the latter deriving significantly lower emissions from red meat. Nevertheless, the Nutritionally Sustainable pattern adhered to more dietary guidelines than other EPs. The results imply that policy instruments should be holistic in naturerather than concentrating on individual food groups.

A reaction-based fluorescent probe for the selective detection of formaldehyde and methylglyoxal via distinct emission patterns

A simple and stable fluorescent probe L based on a novel ortho-diaminorhodamine derivative for discrimination and detection of formaldehyde (FA), methylglyoxal (MGO) and oxalaldehyde (OA) from other aldehydes has been developed. This reaction-based probe, displayed distinct emission patterns for FA (turn-on) and MGO (turn-off) by single wavelength excitation, can be used for imaging of FA and MGO in living cells.

A simple fluorescent off-on probe for the discrimination of cysteine from glutathione.

A simple and stable fluorescent off-on probe for discrimination of cysteine (Cys) from glutathione (GSH) has been developed by combining resorufin with 7-nitrobenzofurazan. The probe, displaying distinct emission patterns for Cys and GSH at just one excitation wavelength, can be used for simultaneous determination of Cys and GSH in human plasma.

Active control of emission directionality of semiconductor microdisk lasers

We demonstrate lasing mode selection in nearly circular semiconductor microdisks by shaping the spatial profile of optical pump. Despite of strong mode overlap, adaptive pumping suppresses all lasing modes except the targeted one. Due to slight deformation of the cavity shape and boundary roughness, each lasing mode has distinct emission pattern. By selecting different mode to be the dominant lasing mode, we can switch both the lasing frequency and the output direction. Such tunability by external pump after the laser is fabricated enhances the functionality of semiconductor microcavity lasers.

Highly luminescent, triple- and quadruple-stranded, dinuclear Eu, Nd, and Sm(III) lanthanide complexes based on bis-diketonate ligands.

The bis(beta-diketone) ligands 1,3-bis(3-phenyl-3-oxopropanoyl)benzene, H(2)L(1) and 1,3-bis(3-phenyl-3-oxopropanoyl) 5-ethoxy-benzene, H(2)L(2), have been prepared for the examination of dinuclear lanthanide complex formation and investigation of their properties as sensitizers for lanthanide luminescence. The ligands bear two conjugated diketonate binding sites linked by a 1,3-phenylene spacer. The ligands bind to lanthanide(III) or yttrium(III) ions to form neutral homodimetallic triple stranded complexes [M(2)L(1)(3)] where M = Eu, Nd, Sm, Y, Gd and [M(2)L(2)(3)], where M = Eu, Nd or anionic quadruple-stranded dinuclear lanthanide units, [Eu(2)L(1)(4)](2-). The crystal structure of the free ligand H(2)L(1) has been determined and shows a twisted arrangement of the two binding sites around the 1,3-phenylene spacer. The dinuclear complexes have been isolated and fully characterized. Detailed NMR investigations of the complexes confirm the formation of a single complex species, with high symmetry; the complexes show clear proton patterns with chemical shifts of a wide range due to the lanthanide paramagnetism. Addition of Pirkle's reagent to solutions of the complexes leads to splitting of the peaks, confirming the chiral nature of the complexes. Electrospray and MALDI mass spectrometry have been used to identify complex formulation and characteristic isotope patterns for the different lanthanide complexes have been obtained. The complexes have high molar absorption coefficients (around 13 x 10(4) M(-1)cm(-1)) and display strong visible (red or pink) or NIR luminescence upon irradiation at the ligand band around 350 nm, depending on the choice of the lanthanide. Emission quantum yield experiments have been performed and the luminescence signals of the dinuclear complexes have been found to be up to 11 times more intense than the luminescence signals of the mononuclear analogues. The emission quantum yields and the luminescence lifetimes are determined to be 5% and 220 micros for [Eu(2)L(1)(3)], 0.16% and 13 micros for [Sm(2)L(1)(3)], and 0.6% and 1.5 micros for [Nd(2)L(1)(3)]. The energy level of the ligand triplet state was determined from the 77 K spectrum of [Gd(2)L(1)(3)]. The bis-diketonate ligand is shown to be an efficient sensitizer, particularly for Sm and Nd. Photophysical studies of the europium complexes at room temperature and 77 K show the presence of a thermally activated deactivation pathway, which we attribute to ligand-to-metal charge transfer (LMCT). Quenching of the luminescence from this level seems to be operational for the Eu(III) complex but not for complexes of Sm(III) and Nd(III), which exhibit long lifetimes. The quadruple-stranded europium complex has been isolated and characterized as the piperidinium salt of [Eu(2)L(1)(4)](2-). Compared with the triple-stranded Eu(III) complex in the solid state, the quadruple-stranded complex displays a more intense emission signal with a distinct emission pattern indicating the higher symmetry of the quadruple-stranded complex.

Using Landsat-5 thematic mapper and digital elevation data to determine the net radiation field of a Mountain Glacier

An accurate evaluation of glacier energy balance requires a precise knowledge of surface-cover albedo and emittance. Usually these values are acquired from field measurements. However, the microclimatological effects in mountainous terrain greatly limit the potential for spatial extrapolation of such a set of values. This study overcomes the problem by using the upward radiance values registered on Landsat-5 Thematic Mapper (TM) images and information on the geometry of ter terrain extracted from a digital elevation model (DEM). Studies were performed in the Athabasca Glacier basin, one of the major glacier outlets of the Columbia Icefield in the Canadian Rocky Mountains. The methodology is composed, first, of an automated procedure for the physiographic description of the glacierized basin (cover type, elevation, slope, aspect, horizon profiles, sky-view factor, and the level of enclosing topography) in order to calculate the effects of topography on the radiation balance for each 30 m pixel. Because glacier surface covers usually have high reflective behaviors or distinct emission patterns, this study puts special emphasis on modelling the amount of terrain-reflected or terrain-emitted radiation received on a particular surface. Second, the topographic correction is applied to values of irradiance computed using the LOWTRAN-6 code, a spectrally based radiative transfer model, and atmospheric radiosonde measurements of the vertical temperature, air pressure, and relative humidity profiles. The measured upward radiance values from TM, corrected for path effects, are used to calculate surface-cover albedo and brightness temperature. Third, the daily net radiation field for snow and ice covers is computed to illustrate the contribution of the estimated surface radiative parameters to the glacier snow-and-ice melt analysis. The resultsshow that the irradiance values are accurately modelled within 10% of the radiattion values acquired from a field pyranometer. The calculated glacial surface-cover reflectance and albedo values compare favorably to published information, whereas the measured surface brightness temperature is well within the expected range of values.

Compositional Ordering in Semiconductor Alloys

AbstractCompositional ordering has been observed in a wide variety of III/V semiconductor alloys as well as in SiGe alloys. The thermodynamic driving force is now understood in terms of minimization of the microscopic strain energy of the bonds in the solid. However, the mechanism leading to the specific ordered structures formed is only now beginning to be understood. It appears to be intimately related to the physical processes occurring on the surface during epitaxial growth, specifically surface reconstruction and the attachment of atoms at steps and kinks. Thus, an improved understanding the ordering process may lead to a better understanding of the surface processes occurring during epitaxial growth from the vapor.This paper will review the current understanding of the ordering process, including discussions of the arrangement of atoms on the surface and the nature of surface steps. The emphasis will be on the use of patterned surfaces to investigate and control the ordered structures formed during organometallic vapor phase epitaxial growth of GaInP. Using photolithography and chemical etching, [110]-oriented steps are formed on the (001) GaAs substrate. The direction of motion of these steps determines the specific variant of the Cu-Pt ordered structure (with ordering on (111) planes) formed. The step density at the edge of the groove apparently determines the degree of order. Highly stepped surfaces suppress ordering or lead to small domains of a single variant. When the steps are very shallow, the large domain of the predominant variant is filled with “inclusions” of the second variant. Step edges that are oriented at nearly 160 from (001) form a {511} variant during growth. This facet is observed to grow at the expense of adjacent (001) surfaces and to produce material that is completely disordered.Growing on intentionally misoriented substrates leads to interesting structures consisting of both large, highly-ordered domains and disordered material. This allows, using cathodoluminescence(CL) imaging, a direct determination of the effect of ordering on the energy band gap. In the GaInP samples studied, the CL images show that the disordered material has a distinct emission pattern consisting of a single, sharp peak at an energy more than 100 meV higher than that observed in the adjacent ordered region.