Temperature Dependence Of Spectra Research Articles

Ultra-wide band near-infrared (NIR) optical thermometry (12-673 K) performance enhanced by Stark sublevel splitting in Er3+ ions near the first biological window in the PbZr0.53Ti0.47O3:Er3+/Yb3+ phosphor.

The fluorescence intensity ratio (FIR) approach, which relies on thermally coupled levels (TCLs), is significantly important for optical thermometry at room temperature and above, but was found to be impractical for low temperature sensing due to limited population density (thermal) or lack of spectrum at extremely low temperatures. Herein, we report a wide temperature range (12-673 K) sensing capability of the PbZr0.53Ti0.47O3:Er3+/Yb3+ (C1:PZT) phosphor utilising the bandwidth of Stark sublevel split near-infrared (NIR) emission bands as one sensing parameter and FIR as another. Motivated by our previous studies on upconversion (UC) and the promising thermometry performance of the C1:PZT phosphor for real time nanothermometer monitoring (using visible TCLs), this work extends to the same thermometry application using UC-NIR emission as TCLs. The temperature-dependent UC spectra were measured across the ranges of 12-313 K and 313-673 K under 980 nm excitation, and their sensing capabilities were thoroughly evaluated. An enveloped single emission band, comprising multiple peaks in the NIR region, was observed and subsequently deconvoluted using Gaussian fitting. These individual peaks were analyzed in relation to Stark sublevel splitting, which was particularly evident at 12 K, and the variations in their full width at half maximum (FWHM) were compared across temperatures up to 313 K. Based on the temperature-dependent bandwidth, two prominent peaks ∼11 655 cm-1 (858 nm) and 11 454 cm-1 (873 nm), were identified as TCL levels, and a sensitivity (Sr) of 0.68 ± 0.01% K-1 at 673 K was observed, making it a suitable thermometer for reading low temperatures using NIR bands.

Black Body-Inspired Chemically Oxidized Nanostructures with Varied Perforations: A New Frontier in Solar Desalination

Ideal black bodies absorb all electromagnetic energy without reflecting it. As it does not reflect or transmit light, it appears black when cold. Heated black bodies emit black body radiation, a temperature-dependent spectrum. This idea helps scientists and engineers comprehend heat radiation and design efficient solar desalination absorbers. This work uses the black body concept to create three non-contact nanostructured single-slope solar stills (NCNSSSs) with varied perforation diameters (2.4 mm, 3.2 mm, and 3.8 mm). The chemical oxidation of mirror-polished perforated stainless steel 304 sheets resulted in highly absorptive top surfaces with 90% absorptivity. The structures’ bottom surfaces were coated with a commercial high-emissivity coating to make them 85% emissive. The developed non-contact nanostructures absorbed maximum solar light and converted it into infrared radiation using a highly emissive bottom coating and a very absorptive top coating. Water, an excellent absorber of infrared (IR) radiation, readily absorbs the IR radiations and evaporates through the perforations, thus producing a desalination effect. Experiments were conducted parallelly in three NCNSSSs under the same weather conditions at three water depths. It was observed that non-contact nanostructure perforation diameters affected solar still performance. The NCNSSS-3 (3.8 mm) achieved a 9.89% and 13.47% higher productivity than the NCNSSS-2 (3.2 mm) and NCNSSS-1 (2.4 mm) at a 5 mm water depth. Additionally, fouling studies, expedited corrosion studies, and water quality assessments (TDS, salinity, fluoride, chlorides, nitrates, sodium) were performed. Water eminence examinations confirmed that the collected freshwater was bacteria-free and safe to drink.

Determining the Electrostatic Contributions of GTPase-GEF Complexes on Interfacial Drug Binding Specificity: A Case Study of a Protein-Drug-Protein Complex.

Understanding the factors that contribute to specificity of protein-protein interactions allows for design of orthosteric small molecules. Within this environment, a small molecule requires both structural and electrostatic complementarity. While the structural contribution to protein-drug-protein specificity is well characterized, electrostatic contributions require more study. To this end, we used a series of protein complexes involving Arf1 bound to guanine nucleotide exchange factors (GEFs) that are sensitive or resistant to the small molecule brefeldin A (BFA). By comparing BFA-sensitive Arf1-Gea1p and Arf1-ARNO with different combinations of four BFA sensitizing ARNO mutations (ARNOwt, ARNO1M, ARNO3M, and ARNO4M), we describe how electrostatic environments at each interface guide BFA binding specificity. We labeled Arf1 with cyanocysteine at several interfacial sites and measured by nitrile adsorption frequencies to map changes in electric field at each interface using the linear Stark equation. Temperature dependence of nitrile vibrational spectra was used to investigate differences in hydrogen bonding environments. These comparisons showed that interfacial electric field at the surface of Arf1 varied substantially depending on the GEF. The greatest differences were seen between Arf1-ARNOwt and Arf1-ARNO4M, suggesting a greater change in electric field is required for BFA binding to Arf1-ARNO. Additionally, rigidity of the interface of the Arf1-ARNO complex correlated strongly with BFA sensitivity, indicating that flexible interfaces are sensitive to disruption upon orthosteric small molecule binding. These findings demonstrate a qualitatively consistent electrostatic environment for Arf1 binding and more subtle differences preventing BFA specificity. We discuss how these results will guide improved design of other small molecules that can target protein-protein interfaces.

Light Emission of Sn/Ge MQW pin Diodes on Si

Si-based photonic integrated circuits (PIC) with optically active components monolithically integrated on a Si chip are considered one of the solutions for the innovation of the next generation of information and communication technology. Si-based photonics opens up new possibilities for applications in data communications, sensor technology, biological and environmental sensing systems, but also future technologies including integrated quantum technologies, optical computing, artificial intelligence-based technologies and neuromorphic photonics. Remarkable advances have been made in key components of Si-based PICs, including high-performance Si-based modulators, photodetectors as well as waveguides. An efficient electrically pumped light source on Si still remains a challenge. The first lasers monolithically integrated on Si were demonstrated at low temperatures using the CMOS (Complementary Metal Oxide Semiconductor)-compatible material system SiGeSn.This paper reports the light emission from multiquantum well (MQW) structures composed of multi-stacked 2 Monolayer (ML) Sn/20 nm Ge layers incorporated into a pin structure. These samples were grown using molecular beam epitaxy. The schematic layer stack is shown in Figure (a). The MQW structure is placed in the intrinsic region of a Ge pin diode on a Si (100) substrate. Figure (b) shows the high-resolution x-ray (HR-XRD) space map of the device structure. The measurement data suggest that the compressively strained 2ML Sn/Ge MQW are grown pseudomorphically on the Ge virtual substrate (VS). Furthermore, the measurement shows clear information about the periodic Sn/Ge structure. In preliminary studies, the wetting layer thickness was determined to be 1.4 ML Sn. Figure (c) shows an atomic force microscopy (AFM) image of Sn dot formation on the Ge (100) surface for 2 ML Sn. The device is processed using a single mesa process with a very low thermal budget.The electroluminescence measurements are carried out in a cryostat, the temperature of which can be continuously regulated from room temperature (RT) to 12 K. The light is collected via a special indium fluoride multimode-fiber and detected with the NIRquest spectrometer in a wide wavelength range between 1000 nm and 2500 nm. In order to understand the influence of the MQW structure, a reference diode with exactly the same growth parameters but without Sn was grown and processed in parallel. Their temperature-dependent EL spectra are shown in figure (d). At RT we see the typical EL spectrum of a Ge diode with the direct band (Γ-HH) and indirect band (L-HH) transition. Due to the indirect semiconductor properties of Ge, the intensity decreases with lower temperatures. The maxima shift towards the blue because of the temperature dependent band gap. At very low temperatures a new luminescence occurs, which we identify as a defect luminescence of the Ge.The temperature-dependent EL spectra of the 2 ML/Ge MQW pin diode are shown in figure (e). Four peaks can be observed depending on the temperature. At RT the Ge peak as in the reference sample can be measured, but with a different intensity ratio. At very low temperatures we find a second, sharper peak next to the defect luminescence peak of Ge (see inset). This shows a direct behavior because the EL intensity increases with decreasing temperature. In the paper we discuss these different peaks in detail and give an interpretation based on photogenerated carrier numbers, temperature dependent occupation and quantum confined radiative transmission probabilities. Figure 1

Elucidation of the Li Storage State and Dynamics in Various Carbon Electrodes by Using 7Li NMR

In recent years, both soft carbons and hard carbons have been considered as potential anode materials for lithium-ion batteries (LIBs) and lithium-ion capacitors (LICs) because of their high capacity and superior rate performance compared to graphite electrodes. To design high power carbon anode, revealing the Li storage state and dynamics in carbon electrodes is required. However, the effect of carbon microstructure on the Li storage state remains unclear because of the complex microstructures of these carbon materials, which consist of a mixture of graphitic and amorphous domains. 7Li NMR is a useful measurement to know the Li storage state because it provides direct observation of Li atoms in carbon microstructures and has the advantage of seeing the dynamics of Li without the process of de-solvation on the electrode-electrolyte interface, compared to electrochemical measurements. In this study, we investigated the Li storage state in soft and hard carbons with different graphitization degrees using 7Li NMR. We obtained information about the Li species, domain size of Li sites, and motion properties by comparing temperature-dependent NMR spectra and spin relaxation time.Graphite, soft carbon (SC), and hard carbon (HC), as well as their graphitized samples by heat treatment at 1500, 2000, and 2500°C, denoted as SCX or HCX (X: Heat treatment temperatures/°C, HTTs), were prepared. The crystallinity of the carbon materials was evaluated using X-ray diffraction (XRD). These carbon samples were electrochemically lithiated by applying a constant current of 50 mA/g to 0.002 V vs. Li/Li+, followed by keeping the potential until a cut-off current of 5 mA/g. The lithiated carbon samples were characterized using 7Li NMR spectroscopy and spin relaxation measurements at different temperatures (103-353 K). The Li self-diffusion coefficient in SC at 343 K was measured by pulsed gradient spin-echo (PGSE) NMR.The 7Li NMR spectrum of lithiated SC was assigned to Li in the turbostratic structure. As the SC heat-treatment temperature increased, the NMR spectra corresponding to the shrinkage of the carbon layer spacing were obtained. The Li in SC2500 was predominantly stored in a graphitic structure and partially in amorphous structures. On the other hand, the Li state in HC showed intercalated Li in the turbostratic layers and quasi-metallic Li clusters. As the HC heat-treatment temperature increased, the peak of quasi-metallic Li clusters disappeared, and the peak of Li in the turbostratic structures remained. Only HC2500 showed a small peak assigned to Li in the graphitic structure, indicating that HC2500 has a distinct graphitic layer structure, as measured by XRD. The average diffusional displacement in the measurement timescale was estimated to be approximately 1 nm below 200 K 1. The chemical exchange occurring at the temperature suggests that the domain size of the Li sites are a few nanometers.The spin-lattice relaxation time (T1) was measured at different temperatures, and the activation energy of each Li species for motion in carbon electrodes were estimated. Li species intercalated in the turbostratic layers indicated similar activation energy for all amorphous carbons, providing an evidence that these Li species in various carbon electrodes have similar restriction and motion properties. Li in graphitic structures on HC2500 showed higher activation energy than amorphous structures and is considered unsuitable for high-rate charge-discharge performance. Y. Fang, K. Peuvot, A. Gratrex, E. V. Morozov, J. Hagberg, G. Lindbergh, and I. Furó, J. Mater. Chem. A, 10, 10069–10082 (2022). Figure 1

(Invited) Synergistic Interactions of Co-Dopants for Phosphor Functionalization

The functionalization of phosphors through co-dopant interactions represents an effective and encouraging avenue for enhancing their luminescent characteristics. Co-doping introduces additional dopant species into the host lattice, leading to intricate interactions that influence the material's luminescence behavior. The synergistic effects arising from co-dopant interactions result in tailored luminescent characteristics, including emission wavelength tuning and improved performance in diverse applications such as lighting, displays, biomedical imaging, temperature measurement, and thermal imaging. By elucidating the intricacies of co-dopant interactions, this research contributes to the rational design and optimization of functionalized phosphors for advanced technological applications. By carefully selecting and controlling the dopants, researchers can tailor the luminescent characteristics of phosphors to meet specific requirements, thereby unlocking their full potential. This presentation focuses primarily on possible advantages of using this approach in luminescence thermometry and thermal imaging.Co-activating phosphors facilitates the development of multifunctional materials with diverse, not only luminescent, properties. By carefully selecting dopant combinations, controlling their concentrations, and managing the technological parameters, precisely designed phosphors exhibiting multi-modal functionalities can be fabricated.In the presentation, we will show examples of the effective use of co-doping phosphors with selected lanthanide ions or a lanthanide and a d-element. An exemplary case is presented in Figure 1, where temperature-dependent luminescence spectra of a triply-activated strontium aluminate phosphor are presented together with the relative thermal sensitivities derived from decay times of the different emissions.The Polish National Science Centre (NCN) financed the research under OPUS grant #UMO2023/49/B/ST5/04265. Figure 1

Perfluorocarbons: a material platform for tunable nonlinear frequency conversion in liquid filled suspended core fibers

This study investigates supercontinuum generation in suspended core fibers filled with perfluorocarbons, highlighting their potential for ultrafast nonlinear frequency conversion. Spectroscopic absorption and refractive index dispersions are analyzed for three perfluorocarbons in the visible and near-infrared. Experiments show that the insertion of these liquids into suspended core fibers changes the dispersion landscape, enabling broadband soliton-based supercontinuum generation from 0.6 µm to 2.4 µm due to the creation of a confined domain of anomalous dispersion in the telecom range. In addition, temperature-dependent output spectrum modulation is demonstrated, highlighting the utility of the platform in photonic applications such as spectroscopy, sensing, and microscopy.

Variable Emissivity Materials for Thermal Radiators: Methods for Characterizing Thermochromic Infrared Surfaces

Thermochromic infrared surfaces have temperature-dependent emissivity spectra that enable radiators to passively respond to changes in the thermal environment. For spacecraft thermal-control applications, these surfaces transition between a high and low thermal emissivity to radiate heat when hot and retain heat when cold. This enhanced temperature-regulation functionality is derived from the intrinsic temperature-dependence of the thermochromic material but introduces complications in thermo-optic characterization and thermal system models. Variable emissivity materials (VEMs) necessitate a new set of thermo-optic characteristics to comprehensively describe the thermal emissivity as a function of both the instantaneous surface temperature and its time history. This research examines the methods of characterizing the thermal emissivity of VEMs using both spectroscopy (an indirect measurement) and radiative calorimetry (a direct measurement). The data are fit to a reduced-order logistic model that captures the primary design features, including the asymptotic emissivity levels and the transition temperature, as well as nonidealities such as transition rates and hysteresis. Together, these tools guide the design of novel VEMs, introduce a standardized set of material descriptors, and enable the representation of VEMs in thermal system models.

White emitting Sr3Ga2Ge4O14: Dy3+ phosphors with high purity and good thermal stability

A series of white emitting phosphors Sr3Ga2Ge4O14: xDy3+ (x = 1, 3, 5, 7, 9 and 11 %) were synthesized by a high-temperature solid-phase method. All samples exhibit two emission peaks at 478 nm and 571 nm, corresponding to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ions, respectively. The optimal doping concentration of Sr3Ga2Ge4O14: xDy3+ phosphors was determined as 7 % mol, and the concentration quenching mechanism is confirmed as a dipole–dipole interaction. Finally, the temperature dependent luminescence spectra indicate that the synthesized Sr3Ga2Ge4O14: 7 % Dy3+ phosphors had good thermal stability.

Superconducting transition of GdBa2Cu3O7-x/La0.7A0.3MnO3 (A=Sr and Ca) bilayers governed by tunable interlayer structural coupling

Bilayers composed of high-Tc cuprate superconductors (HTS) with manganites have garnered significant attention due to the complex interaction between two layers, leading to competition among various ordering phenomena. When HTS and manganties are interfaced, new functionalities can emerge that are absent in the individual components. Notably, epitaxial strain can alter crystal structures and electronic states, significantly impacting superconductivity in HTS/manganite heterostructures. In this study, we analyze the superconducting and ferromagnetic behaviors of GdBa2Cu3O7-x(GdBCO)/La0.7A0.3MnO3(LAMO, where A=Sr and Ca) bilayers, maintain a constant GdBCO thickness of 500 nm while varying the LAMO thickness from 25 to 100 nm. We focus on the local structural correlations between the two layers. Temperature-dependent EXAFS spectra were systematically measured at the Cu and Mn K-edges to investigate the local atomic structures of both layers across the superconducting transition temperature (Tc). Our spectroscopic measurements reveal distinct conformations of the MnO6 octahedra near Tc, which are absent in single-layer LSMO, indicating structural coupling between the layers. Additionally, our magnetization studies show a strong relationship between the structural coupling, magnetic anisotropy (MA), and the superconducting transition of the GdBCO/LAMO bilayers. The additional distortion of the MnO6 octahedra in the GdBCO/LAMO bilayer, likely stemming from structural coupling, may account for the changes in the superconducting transition associated with magnetic anisotropy. This modification of structural coupling can be controlled by adjusting the LAMO thickness, yet it remains highly dependent on the bond geometry of LAMO. The Mn-O bond in LCMO is stiffer than in LSMO, resulting in a smaller change in structural coupling with varying thickness in LCMO compared to LSMO. The disparity in structural coupling directly impacts the magnetic properties of the LAMO layer and subsequently influences the superconducting property ΔTc. Our findings highlight the significance of structural coupling as a critical factor affecting the superconductivity of GdBCO/LAMO bilayers. Furthermore, this study provide foundational insight for designing various applications, such as magnetic sensors and spintronic devices, by enhancing our understanding of local dynamics at the interface between ferromagnets and superconductors.

Divalent tin activator for Nd3+/Yb3+ emission in lanthanum borate glass and its impact on inter-ionic phenomena and thermometry

The co-existence of divalent tin activator and Nd3+/Yb3+ rare earths in the borate glasses were utilized and examined to achieve the effective enhancement of the useful near-infrared emission in the wide spectral region. The UV Sn2+ excitation is extremely relevant for the effectiveness of both (Nd,Yb) near-infrared emission, however, Sn-Nd energy transfer efficiency is particularly prominent. The different advantageous inter-ionic phenomena made it possible to explore the diverse energy transfer routes leading to the population of the relevant ytterbium and neodymium excited states. Consequently, adequate multi-model temperature sensing can be proposed and verified considering single-doped and co-doped borate glass systems. The dissimilar effect of temperature on the complementary Sn2+, Nd3+ and Yb3+ optical transitions was investigated in detail. Employing the temperature-dependent spectra of optically active ions, high values of temperature relative sensitivity (1.3 % K−1) were estimated especially in the physiological range (30 – 75 ⁰C).

A new zero-dimensional hybrid antimony halide of (C25H46N)2SbCl5 with dual-emission and high quantum-efficiency for light-emitting application

Zero-dimensional (0D) organic-inorganic hybrid metal halides (OIHMHs) have received extensive attention due to their excellent photoelectric properties. Herein, a new 0D OIHMH single crystal, (C25H46N)2SbCl5, has been synthesized by slow antisolvent diffusion. In this crystal structure, C25H46N+ (C25H46N+ = Cetyldimethylbenzylammonium cations) cations separated SbCl52− to form a 0D square pyramid structure. (C25H46N)2SbCl5 single crystals (SCs) manifest bright orange-yellow dual-emission bands at 472 and 616 nm, while having a high photoluminescent quantum yield of 97.5 %. The lifetime of high energy (HE) emission and low energy (LE) emission at room temperature is 9.73 ns and 4.61 μs, respectively. Based on lifetime differences and temperature-dependent spectra, the HE emission band is ascribed to singlet self-trapped excitons (STEs), while the LE emission band with a broad full width at half maxima of 136 nm can be attributed to triplet STEs. (C25H46N)2SbCl5 appeared anti-thermal quenching behavior. In accordance with the luminescence characteristics of (C25H46N)2SbCl5, a warm white light-emitting diode device was fabricated with the correlated color temperature of 3410 K, the relevant color coordinate of (0.41, 0.39) and the color rendering index of 95.1, demonstrating (C25H46N)2SbCl5 a promising phosphor for solid-state light-emitting application.

Estimation of vibrational spectra of Trp-cage protein from nonequilibrium metadynamics simulations

The development of methods that allow a structural interpretation of linear and nonlinear vibrational spectra is of great importance, both for spectroscopy and for optimizing force field quality. The experimentally measured signals are ensemble averages over all accessible configurations, which complicates spectral calculations. To account for this, we present a recipe for calculating vibrational amide-I spectra of proteins based on metadynamics molecular dynamics simulations. For each frame, a one-exciton Hamiltonian is set up for the backbone amide groups, in which the couplings are estimated with the transition-charge coupling model for nonnearest neighbors, and with a parametrized map of ab initio calculations that give the coupling as a function of the dihedral angles for nearest neighbors. The local-mode frequency variations due to environmental factors such as hydrogen bonds are modeled by exploiting the linear relationship between the amide C-O bond length and the amide-I frequency. The spectra are subsequently calculated while taking into account the equilibrium statistical weights of the frames that are determined using a previously published reweighting procedure. By implementing all these steps in an efficient Fortran code, the spectra can be averaged over very large amounts of structures, thereby extensively covering the phase space of proteins. Using this recipe, the spectral responses of 2.5 million frames of a metadynamics simulation of the miniprotein Trp-cage are averaged to reproduce the experimental temperature-dependent IR spectra very well. The spectral calculations provide new insight into the origin of the various spectral signatures (which are typically challenging to disentangle in the congested amide-I region), and allow for a direct structural interpretation of the experimental spectra and for validation of the molecular dynamics simulations of ensembles.

Temperature dependence of Fe:ZnSe mid-infrared spectral and laser output properties under ∼4 µm radiation excitation

This paper presents the temperature dependence of the spectroscopic and laser properties of the Fe2+:ZnSe single crystal under excitation by radiation at a wavelength of ∼4.04µm. Excitation was supported by the Er:YAG laser (∼2.94µm) operated in the Q-switched or free-running (FR) mode that pumped the Fe:ZnSe laser cooled by liquid nitrogen to 78 K. This system generated radiation at the wavelength of ∼4.04µm. Temperature dependence of absorption, fluorescence spectra, and fluorescence decay time of Fe2+ ions was measured. The optimal temperature that allows efficient Fe:ZnSe laser system operation with maximum laser output energy was sought in both regimes. It was characterized at a repetition rate of 1 Hz with pulse durations of ∼175ns and ∼155µs in both modes, respectively. The highest laser output energies obtained with the crystal placed in the cryostat in gain-switched (GS) and FR modes were ∼385µJ at 260 K and ∼374µJ at 190 K, respectively. Maximum optical-to-optical efficiencies in the same modes were ∼13% at 260 K and ∼32% at 170 K, respectively. Wide laser radiation oscillation spectra depending on the temperature ranging from ∼4.3µm at 140 K to ∼4.9µm at 340 K obtained with a Gaussian-like beam spatial profile were demonstrated. Under atmospheric conditions at RT, this laser system reached a pulse energy of over 0.5 mJ at ∼4.78µm in ∼135ns pulses, which corresponds to a peak power of ∼3.9kW.

Spectroscopic and computational investigations of isostructural phase transitions in urea 4-carboxyanilinium nitrate having trapped disordered-nitrate ions

Urea 4-carboxyanilinium nitrate (U4-CAN) and its functional groups deuterated counterpart dU4-CAN were studied using infrared vibrational spectroscopy and computational analysis. Using the known frequencies of the parent components the infrared vibrational frequencies of U4-CAN and dU4-CAN were assigned. FTIR study was carried out to understand how the intra-and inter-molecular interactions in the parent components are affected by U4-CAN co-crystal formation. U4-CAN undergoes isostructural phase transition at 359.1 K. Hence FTIR spectra of U4-CAN were also recorded at different temperature in the range 293 K to 368 K. The interesting observation seen with temperature dependent spectra was:(i) the spectral band intensity increased with increasing temperature and (ii) the peak position of almost all bands did not change in the entire temperature range studied. This results corroborate with the reported structural data of U4-CAN were in it is found that the structural phase transition is isostructural. Hence the crystal structure in the range 293 K to 368 K has same space group and differ only in few hydrogen bond interactions. In order to carry out various theoretical calculation of U4-CAN, the crystallographically obtained structure at 293 K was optimized by density functional theory (DFT) with B3LYP/6–311 G basis set. The theoretical calculated vibration spectra were similar to the experimentally obtained FTIR data. The fingerprint plot of U4-CAN obtained using CrystalExplorer 21 software indicated that the most prominent interaction corresponds to the short O···H contact. Noncovalent interaction (NCL) study indicated that the U4-CAN complex has steric, van der Waals and hydrogen bond interactions and the NH⋅⋅⋅⋅⋅O hydrogen bond interaction between NH3+/ NH2 moieties and NO3- was the strongest. From QTAIM calculation the strongest hydrogen bond interaction in U4-CAN complex was for NH.....O and NH.....N interactions.

Defect level induced negative thermal quenching of β-Ba3LuAl2O7.5: Yb3+, Er3+ phosphor

Temperature-dependent behavior of phosphors has recently attracted significant research attention. This is due to the widespread applications of phosphors. Unfortunately, the thermal quenching effect in many phosphors greatly limits their performance at high temperatures. Herein, negative thermal quenching phosphor β-Ba3LuAl2O7.5: 0.3Yb3+, 0.03Er3+ is synthesized using the high-temperature solid-state method. X-ray Rietveld refinement and EPR results indicate the defect state of oxygen vacancy. Temperature-dependent upconversion luminescence spectra demonstrate that the green and red emission intensities increase with temperature to reach maximums at 398 K and 348 K respectively. Diffuse reflectance spectrum and downshifting luminescence spectrum prove that the defect state is near the 4F7/2 state of Er3+ ions. The defect state traps electrons at room temperature and releases them to populate the 4F7/2 state of Er3+ ion at elevated temperatures to cause the observed thermal enhancement of upconversion luminescence. This material's negative thermal quenching effect makes it a suitable candidate for applications in displays and anti-counterfeiting.

Temperature dependence of the near infrared absorption spectrum of single-wall carbon nanotubes dispersed by sodium dodecyl sulfate in aqueous solution: experiments and molecular dynamics study.

Single-wall carbon nanotubes (SWCNT) dispersed in water with the help of sodium dodecyl sulfate (SDS) surfactants exhibit a temperature dependent near infrared (NIR) exciton spectrum. Due to their biocompatibility and NIR spectrum falling within the transparent window for biological tissue, SWCNTs hold potential for sensing temperature inside cells. Here, we seek to elucidate the mechanism responsible for this temperature dependence, focusing on changes in the water coverage of the SWCNT as the surfactant structure changes with temperature. We compare optical absorption spectra in the UV-Vis-IR range and fully atomistic molecular dynamics (MD) simulations. The observed temperature dependence of the spectra for various SWCNTs may be attributed to changes in the dielectric environment and its impact on excitons. MD simulations reveal that the adsorbed SDS molecules effectively shield the SWCNT, with ~ 70% of water molecules removed from the first two adlayers; this coverage shows a modest temperature dependence. Although we are not able to directly demonstrate how this influences the NIR spectrum, this represents a potential pathway given the strong influence of the water environment on the excitons in SWCNTs. Optical absorption measurements were carried out in the UV-Vis-NIR range using a Varian Cary 5000 spectrophotometer in a temperature-controlled environment. PeakFit™ v. 4.06 was used as peak-fitting program in the spectral range 900-1400nm (890-1380meV) as a function of the temperature. Fully atomistic molecular dynamics simulations were conducted using the NAMD2 package. The CHARMM force field comprising two-body bond stretching, three-body angle deformation, four-body dihedral angle deformation, and nonbonded interactions (electrostatic and Lennard-Jones 6-16 potentials) was employed.

Novel self-activated red-emitting CsSrEu (PO3)6 phosphor: Synthesis, luminescent properties and enhancement by partially anion substitution

Novel self-activated red-emitting CsSrEu(PO3)6 was synthesized by high-temperature solid-phase method, and their enhanced luminescence were obtained by the modification of local structure. CsSrEu(PO3)6 was efficiently excited at 394 nm and emitted bright red light centered around 609 nm. Their luminescence intensity of CsSrEu(PO3)6 phosphor substituted by (BO3)3-/(SiO4)4- is about 1.346 or 1.454 times of the initial values respectively. The temperature-dependent luminescent spectra show that the emission intensity of CsSrEu(PO3)6 substituted by (BO3)3-/(SiO4)4- at 423 K remains 90.9 % and 86.6 % of the initial value respectively. The internal quantum efficiency is 88.4 % and 83.5 % respectively. White light-emitting diode fabricated by the phosphors, commercial blue-green phosphors and 395 nm chips show high color quality. The overall results indicate that the CsSrEu(PO3)6 phosphor substituted by (BO3)3-/(SiO4)4- group is promising candidate in warm white LED and anionic group substitution can be used to optimize luminescent properties of phosphors.

Glass transition temperature of Agar-Reduced Graphene Oxide (RGO) Composites using 2-D contour mapping of temperature dependent FTIR spectra

In the present work, composites of Reduced Graphene Oxide (RGO) and Agar have been synthesized via the solution cast method and their structural, thermal and dielectric properties are studied. UV–Visible, X Ray Diffraction (XRD), Raman Spectroscopy and Fourier Transform Infrared (FTIR) have been employed for analyzing structural properties of the prepared samples. Analysis of different peaks in XRD and Raman Spectra suggests the interaction of RGO layers with Agar at the molecular level. FTIR spectra indicate that interaction of Agar with RGO occurs through hydrogen bonding linkage. Further, the Glass transition temperature (Tg) of prepared samples has been determined using 2D contour mapping from temperature-dependent FTIR spectra as well as from the Differential Scanning Calorimetry (DSC)technique. Values of Tg obtained from both techniques have been found in close agreement with each other. In addition to that, value of Tg of Agar increases from 72 °C to 80 °C as an effect of 2 wt.% RGO loading indicating the improvement in the thermal behavior of Agar. Moreover, the dielectric behavior of as-prepared composites demonstrate that the dielectric constant of these composites has been increased in comparison to pure Agar.

VUV absorption spectra of water and nitrous oxide by a double-duty differentially pumped gas filter.

The differentially pumped rare-gas filter at the end of the VUV beamline of the Swiss Light Source has been adapted to house a windowless absorption cell for gases. Absorption spectra can be recorded from 7 eV to up to 21 eV photon energies routinely, as shown by a new water and nitrous oxide absorption spectrum. By and large, the spectra agree with previously published ones both in terms of resonance energies and absorption cross sections, but that of N2O exhibits a small shift in the {\tilde{\bf D}} band and tentative fine structures that have not yet been fully described. This setup will facilitate the measurement of absorption spectra in the VUV above the absorption edge of LiF and MgF2 windows. It will also allow us to carry out condensed-phase measurements on thin liquid sheets and solid films. Further development options are discussed, including the recording of temperature-dependent absorption spectra, a stationary gas cell for calibration measurements, and the improvement of the photon energy resolution.