Decrease In Emission Intensity Research Articles

Supramolecular Interactions Induce Unexpectedly Strong Emissions from Triphenylamine-Functionalized Polytyrosine Blended with Poly(4-vinylpyridine).

In this study, we synthesized a triphenylamine-functionalized polytyrosine (PTyr-TPA) through living ring opening polymerization with 4,4′-diamino-4″-methoxytriphenylamine (TPA-NH2) as an initiator, and used Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopy to confirm the chemical structure. Photoluminescence spectroscopy revealed the photophysical properties of TPA-NH2 and PTyr-TPA and suggested that TPA-NH2 exhibited aggregation-caused quenching; in contrast, attaching the initiator to the rigid rod conformation of the PTyr segments caused PTyr-TPA to display aggregation-induced emission behavior. Differential scanning calorimetry revealed single glass transition temperatures for miscible PTyr-TPA/P4VP blends, the result of intermolecular hydrogen bonding between the pyridine units of P4VP and the phenolic OH units of PTyr-TPA, as confirmed through FTIR spectroscopic analyses. Furthermore, the chain behavior of PTyr-TPA transformed from a β-sheet conformation to random coils after blending with P4VP, as determined using wide-angle X-ray diffraction. These findings suggest that the decreased emission intensity of PTyr-TPA resulted from release of the restricted intramolecular rotation of the triphenylamine moiety in the polypeptide center.

Monitoring oxidation changes in commercial extra virgin olive oils with fluorescence spectroscopy-based prototype

Maintaining the quality of extra virgin olive oils (EVOOs) in the current globalised market is a key challenge for the olive oil manufacturers. To maintain the quality, one major factor is to resist its oxidation during processing and storage. Resisting the oxidation in EVOOs is a challenging task requiring control of different physical and chemical factors. However, rapid, real-time, and non-destructive monitoring the oxidation in EVOOs could support in maintaining its quality during storage. The present study utilises a novel right-angle fluorescence spectroscopy-based prototype for rapid monitoring of oxidation changes in three different EVOOs varieties (Arbequina, Picual, and Cornicabra) during storage. Furthermore, the effects of light exposure on oxidation of EVOOs were also studied. Two major changes in the fluorescence spectra of EVOO samples were mainly observed: a decrease in fluorescence emission intensity at 671 nm, and an increase in fluorescence intensities at 420, 440, 464, and 515 nm. These two changes were related to a decrease in chlorophyll content and parallel formation of oxidation products. The formation of oxidation products was found to have a linear relationship with the decrease in chlorophyll content. Out of the three, the Cornicabra variety showed the highest rate of oxidation changes. Furthermore, the EVOOs degraded rapidly when get exposed to light. In a fast and non-destructive manner, the fluorescence spectroscopy-based prototype successfully monitored the oxidation changes in the EVOOs.

Crystal structure, theoretical and experimental electronic structure and DNA/BSA protein interactions of nickel(II) N2O2 tetradentate Schiff base complexes

Nickel(II) allyl arm Schiff base complexes ([NiL1] and [NiL2]) were synthesized and characterized by elemental analysis and ESI-MS, FT-IR, UV–Vis and 1H NMR spectral techniques. The structure of [NiL1] and [NiL2] were analyzed by single crystal X-ray crystallography reveal nickel complexes have slightly distorted square planar geometry around the metal ions. DFT calculations for [NiL1] and [NiL2] in gas phase were performed using SDD basis set for nickel atom and 6-311G(d,p) basis set for the remaining atoms and also at PW91/TZ2P/ZORA level. The electronic transitions of the complexes in acetonitrile were studied by TD-DFT calculations. The energy decomposition analysis was performed to understand the nature of bonding between Ni(II) and Schiff bases (H2L1 and H2L2) suggests that more covalent nature of bonding is in metal complexes. Hypochromism in absorption spectra, emission intensity decrease in EB-DNA complex and DNA viscosity increase by the addition of increasing concentration of the metal complex indicate intercalative mode of binding of the complex with DNA. The binding constants calculated are of the order of 105M−1. The BSA protein binding behavior with [NiL1] and [NiL2] were investigated using absorption and fluorescence titration experiments show alteration in protein’s microenvironment. Also, molecular docking studies were performed to understand the DNA-complex interactions.

Organic petrology and micro-spectroscopy of Tasmanites microfossils: Applications to kerogen transformations in the early oil window

The transformation of kerogen to hydrocarbons in the early stages of oil generation is critical for understanding the resource potential of liquid-rich shale plays. Organic petrology commonly is used for visual evaluation of type, quality, and thermal maturity of organic matter, but the relationship of visual petrographic changes to chemical transformations is not well characterized. To improve understanding of these processes, organic-walled microfossils of the unicellular green alga Tasmanites (composed of algaenan) in Upper Devonian Ohio Shale (Huron Member, Appalachian Basin) were analyzed by micro-spectroscopy techniques including micro-Fourier transform infrared (micro-FTIR), X-ray photoelectron (XPS), electron probe microanalysis (EPMA), and fluorescence. Immature to mid-oil window maturation sequences of core and outcrop samples with solid bitumen reflectance (BR) and vitrinite reflectance (VR) values ranging from 0.45 to 0.80%Ro were used. Hydrous pyrolysis was applied to low-maturity (BR: 0.25–0.39%Ro) Huron and time-correlative New Albany shale samples to create similar artificial maturation sequences for comparison. Micro-FTIR spectroscopy revealed a decrease in the CH2/CH3 ratio with increasing maturity, indicating Tasmanites aliphatic chains become shorter and more branched. Oxygenated functional groups decreased relative to aliphatic stretching bands and increased aromaticity was noted at the highest maturities. In samples that were pyrolyzed for 72h at temperatures of 300–320°C (BR: 0.56–0.68%Ro), Tasmanites showed similar trends, whereas at pyrolysis temperatures of 340°C and higher (BR>1.0%Ro), Tasmanites was pseudomorphed by accumulations of solid bitumen, carbonate and sulfide. Replacement of Tasmanites by these phases in hydrous pyrolysis experiments ≥340°C and its absence at higher maturities (peak oil, VR and BR≥0.9%Ro) in naturally matured samples, as documented in a previous study, implies that a large fraction of the algaenan component of original organic carbon is converted to petroleum during thermal maturation. XPS analysis indicated the molar proportion of aliphatic carbon increases with increasing thermal maturity, accompanied by decreases in oxygenated functional groups and olefinic carbon. EPMA of Tasmanites showed highest concentrations of S, with concentrations of redox-sensitive trace elements U, Mo, Ni and V generally at or below detection limits. Decrease in organic S with increasing thermal maturity may be related to cleavage of Tasmanites at CS linkages; however, this relationship was inconsistent and presence of adjacent or entrained nanoscale silicate or sulfide phases may impact measured trace element concentrations. Fluorescence microscopy and spectroscopy showed a red shift in spectral maxima and decreased emission intensities with increasing maturity, interpreted as due to non-radiative energy loss possibly because of increased aromaticity. Collectively, these results provide new insights into the in situ chemical transformations that accompany petrographic changes as oil-prone kerogen converts to petroleum with thermal advance from immature conditions into the mid-oil window.

Tunable emitting phosphors K3Gd(PO4)2: Tm3+-Dy3+ for light-emitting diodes and field emission displays

Spectroscopic properties of K3Gd(PO4)2: Tm3+-Dy3+ under ultraviolet (UV) light and low-voltage electron beam excitations were investigated. Upon direct excitation Tm3+ from its 6F6 level to 1D2 level, the decrease of emission intensity and lifetime of Tm3+ 1D2-3F4 emission with increasing concentration of Dy3+ in K3Gd(PO4)2: Dy3+, Tm3+ confirmed the occurrence of energy transfer from Tm3+ to Dy3+. Besides, K3Gd(PO4)2: Dy3+, Tm3+ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm3+. When 1% Tm3+ and 8% Dy3+ were codoped in the K3Gd(PO4)2, intensive white emitting light with CIE of (0.338, 0.347) was achieved upon 358 nm excitation. The cathodoluminescence spectra of K3Gd(PO4): Tm3+, Dy3+ phosphors as a function of accelerating voltage and filament current were also measured. Under low-voltage electron-beam excitation, K3Gd(PO4)2: Tm3+, Dy3+ phosphors exhibit excellent tunable emitting property. All of the above results reveal that the as-prepared K3Gd(PO4)2: Tm3+, Dy3+ phosphors have potential applications in white LEDs and FEDs.

FRET- based immunoassay using CdTe and AuNPs for the detection of OmpW antigen of Vibrio cholerae

In the past few decades, nanoscales Förster resonance energy transfer (FRET) based techniques have been used to improve the bioanalysis applications. In this study a new FRET immunosensor based on CdTe was developed for detection of Vibrio cholerae outer membrane protein W (OmpW). The assay is based on competitive quantum dot fluorescence quenching by Au nanoparticles (AuNPs). AuNPs with maximum absorption around 517nm and average size of 14.5nm was synthesized using the Turkevich method. The Surface of particles was modified with 11-MUA and was conjugated with OmpW via amine coupling method. Formation of Au-OmpW was confirmed by FTIR. Carboxyl functionalized CdTe was conjugated to polyclonal anti-OmpW in the same way. Due to interaction of OmpW with its related antibody, the distance between two particles becomes less than 10nm and the energy of CdTe transfers to AuNP and cause to decrease of emission intensity. The more the ratio of Au-OmpW, the more quenching of fluorescent emission of CdTe-anti-OmpW via FRET process. By addition of free OmpW, competition between free and conjugated OmpW will cause separation of Au-OmpW from CdTe-anti-OmpW and results in fluorescent recovery. Increase in fluorescence intensity is proportional to the concentration of free OmpW in the analyte solution. The lowest concentration of OmpW that was detected in this study was 2nM and the linear range of detection was determined to be 2–10nM. This method is simple, fast and sensitive and also doesn’t need any washing step and requires no specific equipment.

The Tetraarylpyrrolo[3,2-b]pyrroles-From Serendipitous Discovery to Promising Heterocyclic Optoelectronic Materials.

Progress in organic optoelectronics requires compounds possessing a suitable combination of photophysical and electronic properties. Another key constraint encompasses the availability of feasible, and hopefully scalable, synthetic procedures for preparing the molecular scaffolds of interest. A multicomponent reaction of aromatic aldehydes, aromatic amines, and butane-2,3-dione that was discovered in 2013 gives straightforward access to previously unavailable 1,2,4,5-tetraarylpyrrolo[3,2-b]pyrroles. These dyes are examples of heteropentalenes-a class of 10-π-electron aromatic compounds. The unsurpassed variety of aromatic aldehydes and primary aromatic amines, which are commercially available or easy to prepare, allows for potential routes to thousands of 1,2,4,5-tetraarylpyrrolo[3,2-b]pyrroles that are currently unknown. This synthetic procedure offers a means for preparing the pyrrolopyroles in gram quantities and isolating them by simple filtration. Typically, the construction of an aromatic core is merely the first phase in a long procedure toward multistep functionalization. Conversely, the synthesis of 1,2,4,5-tetraarylpyrrolo[3,2-b]pyrroles leads to preinstalled substituents in frames with C2 symmetry, which "opens Sesame" to a wealth of structural possibilities. In addition, steric hindrance of the aldehyde components, rather than presenting a problem, is beneficial for increasing the yields of the products. This feature provides invaluable routes for the synthesis of a broad range of π-extended systems possessing the pyrrolo[3,2-b]pyrrole core in just a few steps. Indeed, this approach has enabled the preparation of a large number of previously unknown ladder-type heteroacenes possessing additional rings based on carbon-carbon, carbon-nitrogen, and nitrogen-nitrogen double bonds as well as nitrogen-boron single bonds. This set of chromophores includes planar and curved structures bearing up to 14 conjugated rings. 1,2,4,5-Tetraarylpyrrolo[3,2-b]pyrroles manifest broad absorption bands between about 300 and 450 nm, strong violet-blue or blue fluorescence with typical quantum yields of ∼60%, significant Stokes shifts ranging between 3000 and 5800 cm-1, and emission while in the solid state. Should the two peripheral aryl groups have an electron-deficient character, the two-photon absorption cross section also becomes pronounced, i.e., ∼400 GM. Perhaps the most important feature of these dyes is their strong solvatofluorochromism, which predestines their value as environment-sensitive probes. Extension of the π-conjugation of 1,2,4,5-tetraarylpyrrolo[3,2-b]pyrroles enables further modifications of their photophysical properties, such as shifting the emission bathochromically, increasing the Stokes shift beyond 10 000 cm-1, and attaining solvatofluorochromism for curved, butterfly-shaped analogues without a decrease in emission intensity when the solvent polarity is increased. Common features of these chromophores include a significant difference between the geometries of their relaxed ground and relaxed excited states as well as strong electronic coupling through their aromatic cores. Past and future intense exploration of the wide chemical space built around the pyrrolo[3,2-b]pyrrole skeleton offers unprecedented opportunities for comprehensive elucidation of how photoexcitation increases the electronic coupling through biaryl linkages.

Ultraviolet Emission From Resonant Tunnelling Metal–Insulator– Semiconductor Light Emitting Tunnel Diodes

Strong room-temperature electroluminescence at 365 nm has been demonstrated from simple Au/AlN/ n -GaN metal–insulator–semiconductor (MIS) light emitting diodes, which do not contain p -doped material. Current-voltage and electroluminescence data indicate that an AlN insulating layer thickness of 10 nm results in optimized diode behavior and maximum ultraviolet emission: At lower thicknesses carriers tunnel easily through the barrier, whereas at greater thicknesses the forward resistivity is excessively high. A decrease in emission intensity was observed at high injection currents due to Fowler–Nordheim tunnelling. However the device efficiency was found to improve by a factor of 10 when the AlN layer and the metal contact layer were deposited without breaking vacuum, thereby preventing any contamination or oxidation of the AlN surface. Additionally, this MIS device showed clear resonant tunnelling characteristics which are correlated with the enhanced light emission intensity.

Annealing of dry etch damage in metallized and bare (-201) Ga2O3

The surface of single-crystal (-201) oriented β-Ga2O3 was etched in BCl3/Ar inductively coupled plasmas under conditions (an excitation frequency of 13.56 MHz, a source power of 400 W, and a dc self-bias of −450 V) that produce removal rates of ∼700 Å min−1. Annealing at 400 and 450 °C was carried out after etching on Ni/Au Schottky diodes formed on the surface either before or after the annealing step. Current–voltage (I–V) measurements were used to extract the Schottky barrier height (Φ), diode ideality factor (n), and reverse breakdown voltage (VRB) for plasma damaged diodes after annealing. Annealing at 450 °C was found to essentially restore the values of Φ, n, and VRB to their reference (unetched) values on samples metallized after etching and annealing. Thermal annealing at either temperature of metallized diodes degraded their reverse breakdown voltage, showing that Ni/Au is not stable on β-Ga2O3 at these temperatures. Photoluminescence revealed a decrease in total emission intensity in the near band-edge region after the introduction of etch damage. Electron beam-induced current measurements showed a decrease in the minority carrier diffusion length from 350 μm in the control sample to 311 μm in the etched sample.

Luminescence and luminescence quenching of efficient GdB5O9:Eu3+ red phosphors

This work concerns polycrystalline GdB5O9:Eu3+, which were made as single phase samples by a simple aqueous sol-gel method. The phase formation of the samples was monitored by X-ray diffraction measurements. Excitation of the synthesized phosphors with near-UV radiation resulted in bright red emission with excellent colour saturation. The colour coordinates were relatively stable regardless Eu3+ concentration and temperature increase. Furthermore, under 394.5nm excitation quantum efficiency of the phosphors doped with up to 25% Eu3+ is 100%, what is excellent for practical application. The endmember of the series, EuB5O9, possessed quantum efficiency of about 64%, which is still high for a compound with such large Eu content. Temperature dependent emission spectra revealed emission intensity decrease upon increasing temperature and that the samples doped with 1%, 50%, and 100% Eu3+ lose half of their photoluminescence efficiency at 891, 603, and 515K, respectively. Besides, the unique emission spectra profile makes these luminescent materials very attractive for application in luminescent security pigments.

Intrinsic relationship between photoluminescence and electrical characteristics in modulation Fe-doped AlGaN/GaN HEMTs**Project supported by the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91433112), the National Natural Science Foundation of China (Grant No. 51672163), and the Key Laboratory of Functional Crystal Materials and Device (Shandong University, Ministry of Education), China (Grant No. JG1401).

The photoluminescence (PL) and electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) with different Fe doping concentrations in the GaN buffer layers were studied. It was found that, at low Fe doping concentrations, the introduction of Fe atoms can result in a downward shift of the Fermi level in the GaN buffer layer, since the Fe atoms substitute Ga and introduce an Fe Ga acceptor level. This results in a decrease in the yellow luminescence (YL) emission intensity accompanied by the appearance of an infrared (IR) emission, and a decrease in the off-state buffer leakage current (BLC). However, a further increase in the Fe doping concentration will conversely result in the upward shift of the Fermi level due to the incorporation of O donors under the large flow rate of the Fe source. This results in an increased YL emission intensity accompanied by a decrease in the IR emission intensity, and an increase in the BLC. The intrinsic relationship between the PL and BLC characteristics is expected to provide a simple and effective method to understand the variation of the electrical characteristic in the modulation Fe-doped HEMTs by optical measurements.

Improvement of Green Upconversion Monochromaticity by Doping Eu3+ in Lu2O3:Yb3+/Ho3+ Powders with Detailed Investigation of the Energy Transfer Mechanism.

The monochromaticity improvement of green upconversion (UC) in Lu2O3:Yb3+/Ho3+ powders has been successfully realized by tridoping Eu3+. The integral area ratio of green emission to red emission of Ho3+ increases 4.3 times with increasing Eu3+ doping concentration from 0 to 20 mol %. The energy transfer (ET) mechanism in the Yb3+/Ho3+/Eu3+ tridoping system has been investigated carefully by visible and near-infrared (NIR) emission spectra along with the decay curves, revealing the existence of ET from the Ho3+5F4/5S2 level tothe Eu3+5D0 level and ET from the Ho3+5I6 level to the Eu3+7F6 level. In addition, the population routes of the red-emitting Ho3+5F5 level in the Yb3+/Ho3+ codoped system under 980 nm wavelength excitation have also been explored. The ET process from the Yb3+2F5/2 level to the Ho3+5I7 level and the cross-relaxation process between two nearby Ho3+ ions in the 5F4/5S2 level and 5I7 level, respectively, have been demonstrated to be the dominant approaches for populating the Ho3+5F5 level. The multiphonon relaxation process originating from the Ho3+5F4/5S2 level is useless to populate the Ho3+5F5 level. As the energy level gap between the Ho3+5I7 level and Ho3+5I8 level matches well with that between Eu3+7F6 level and Eu3+7F0 level, the energy of the Ho3+5I7 level can be easily transferred to the Eu3+7F6 level by an approximate resonant ET process, resulting in a serious decrease in the red UC emission intensity. Since this ET process is more efficient than the ET from the Ho3+5F4/5S2 level to the Eu3+5D0 level as well as the ET from the Ho3+5I6 level to the Eu3+7F6 level, the integral area ratio of green emission to red emission of Ho3+ has been improved significantly.

A Multi-region Structural Decomposition Analysis of Global CO2 Emission Intensity

This paper studies changes in global and national CO2 emission intensities using the multi-region structural decomposition analysis (SDA) technique. Emission intensities such as the ratio of CO2 emissions to GDP have lately been widely used to characterize national emission performance. Meanwhile the impact of international trade has been found to be important in global emission accounting. It is therefore important to analyze changes in emission intensities by taking trade into consideration. In this study, we first propose two SDA models, one at the global level and the other at the country level, to quantify both the domestic and trade related effects on an intensity indicator. The models are then used to study changes in global and countries' CO2 emission intensities from 2000 to 2009. The results show that sectoral emission efficiency improvement was the main contributor to the slight decrease in global emission intensity during the period, while international trade marginally hampered improvement of global emission intensity. Comparisons of the performance between emerging economies and advanced economies reveal the importance of production structure and final demand structure in emission intensity reduction. The policy implications of the findings are presented.

On the influence of calcium substitution to the optical properties of Cr3+ doped SrSc2O4

Cr3+ doped (Sr,Ca)Sc2O4 samples were synthesized and investigated in view of their potential application as luminescent converters for high power broad band near infrared (NIR) sources. The synthesis of the Cr3+ activated MSc2O4 (M=Ca, Sr) samples was performed by solid state reactions. Obtained powders show broad band near infrared emission between 700 and 1000nm under excitation in the blue spectral range. The emission is assigned to the intraconfigurational (3d3) 4T2→4A2 transition on Cr3+. As the calcium concentration in SrSc2O4 was increased, a blue shift of the emission spectra was observed. In order to gain insight in the luminescence properties, the crystal field strength, Racah parameters and phonon coupling parameters were examined. Additionally, the influence of temperature in the range between 4 and 500K on the photoluminescence of the CaSc2O4:Cr3+ and SrSc2O4:Cr3+ was investigated. At 4K a μs decay time typical of Cr3+ broad band d-d emission was observed. Between 70 and 350K the decay time and emission intensity decrease due to thermal quenching. The large Stokes shift of the Cr3+ emission (~3000cm-1) combined with the low energy position of the 4T2 excited state causes non-radiative relaxation to the ground state, already below room temperature. The low thermal quenching temperature of broad band NIR emission is a general problem and the present results provide insight in factors determining thermal quenching.

Study of Hydrogen and Oxygen and Its Reaction With Host Elements in Sandstone by Laser-Induced Breakdown Spectroscopy (LIBS)

A study of hydrogen and oxygen and its reaction with host elements in a sandstone has been done by laser-induced breakdown spectroscopy (LIBS). The sandstone was irradiated by Nd-YAG laser (1064 nm, 7 ns) with varied energy of 60 mJ till 140 mJ in surrounding air gas pressure of 1 atm and produced plasma. The emission intensities of hydrogen H I 656.2 nm and oxygen O I 777.2 nm in the plasma were captured by HR 2500+ spectrometer and displayed in intensity as a function of wavelength. The data show that the emission intensities of hydrogen and oxygen increase with increasing laser energy at a gradient of 5.4 and 11.8 respectively every increasing laser energy of 20 mJ. To characterize the reaction process between hydrogen and oxygen with the host elements of the sandstone, a 0.2 ml demineralized water was dropped on the sandstone surface and was analyzed as a function of delay time reaction and temperature. The data show that the oxidation reaction between host elements and oxygen occurred after 25 minutes that the oxygen emission intensity increases and the hydrogen emission intensity decreases. Another data also show that the increasing temperature of sandstone until 80 C increased intermolecular bond between oxygen and host element and dehydrogenation took place after reaching this temperature

Down-conversion from Er 3+ -Yb 3+ codoped CaMoO 4 phosphor: A spectral conversion to improve solar cell efficiency

Abstract The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er 3+ and Yb 3+ in CaMoO 4 :Er 3+ , Yb 3+ phosphors. We have successfully synthesized a series of Er 3+ doped and Yb 3+ codoped CaMoO 4 phosphors by hydrothermal method. The down-conversion of Er 3+ -Yb 3+ combination with CaMoO 4 phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er 3+ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to 4 S 3/2 → 4 I 15/2 transition. The addition of Yb 3+ into Er 3+ doped CaMoO 4 attribute an emission at 980 nm due to 2 F 5/2 → 2 F 7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er 3+ to Yb 3+ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb 3+ ion. The lifetime measurement also reveals the energy transfer from Er 3+ to Yb 3+ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively.

Highly blue emission of ZnO nanoparticles embedded in a SiO2 matrix

The main drawbacks of fluorescent ZnO nanoparticles in practical optoelectronic applications are fast particle growth and agglomeration in water, causing a periodic decrease of light emission intensity. In this work, ZnO nanoparticles were successfully embedded within a silica matrix to prevent their agglomeration. The ZnO NPs were synthesized by the polyol method, using ethylene glycol and glycerol in sizes ranging from 5–6 nm. The as-obtained ZnO particles were dispersed in an amorphous silica matrix under three different ZnO:SiO2 molar ratios: 20:80, 15:85 and 10:90. With the aim of enhancing the luminescent properties of the ZnO@SiO2 composites, various annealing treatments in the range of 150–210 °C were carried out. The chemical analyses of the bare ZnO and the composites were carried out by Fourier transform infrared spectroscopy, which confirmed the presence of functional groups attached to the ZnO surface. By means of thermogravimetric analysis, it was determined that the evaporation of solvents shifted to lower temperatures (180 °C) when silica was added to the ZnO colloidal solution. By means of photoluminescence, a bright blue emission, centered at 440 nm, was observed in all of the samples, even at high temperatures (i.e., 210 °C); only a red shift of 20 nm was observed. Interestingly, the emission intensity of the sample 20:80, when annealed at 170 °C for 4 h, was enhanced 2.6 times, compared to the bare ZnO.

Lead Tightly Associates to Neuronal Calcium Sensor (NCS) Protein Dream and Promotes Structural Changes Analogous to Calcium Bound Dream

Downstream regulatory element antagonist modulator (DREAM), is a 29 kDa Ca2+ binding protein that controls several neurological processes including gene expression, apoptosis, and modulation of Kv4 voltage channels. Here we demonstrate that Pb2+ binds to EF-hands in DREAM with an equilibrium affinity higher than that determined for Ca2+. Pb2+ association triggers changes in the secondary and tertiary structure of the protein that are analogous to those observed in Ca2+ bound DREAM based on the Trp 169 emission data and CD spectra. Namely, Pb2+ binding to DREAM leads to a decrease of Trp169 emission intensity and decrease in the CD signal at 220 nm. The hydrophobic cavity in the C- terminal domain of DREAM is solvent exposed in the presence of Pb2+ as determined using a hydrophobic probe 1, 8-ANS. The Kd values for 1, 8-ANS binding to Ca2+ and Pb2+ bound DREAM were found to be similar; 73±10 μM and 103±10 µM, respectively. Pb2+ binding to DREAM also modulates DREAM interactions with intracellular partners. For example, titrations of presenilin-1 with DREAM in the presence of Ca2+ or Pb2+ showed that Pb2+ bound DREAM has a similar affinity for presenilin-1 (Kd = 2.44±0.19 μM) as Ca2+ bound DREAM (Kd = 6.23±1.60 μM). The impact of Pb2+ association on DREAM conformational dynamics was proved in time-resolved fluorescence studies and the thermodynamic parameters for Pb2+ association to EF-hands were obtained using isothermal titration calorimetry (ITC). Those results indicate that DREAM and likely other neuronal calcium sensors bind Pb2+ with a high affinity and Pb2+ association to neuronal calcium sensors may contribute to lead-induced neurotoxicity.

Fluorescence spectroscopic investigation of bitumen aged by field exposure respectively modified rolling thin film oven test

During ageing the chemical composition of bitumen changes, which is reflected by the change in the distribution of bitumen fractions. By measuring the spectrum of fractions, and by correlating fractional changes during ageing within bitumen with the corresponding spectra, a connection between bitumen’s age and the fluorescence spectrum can be drawn. While the age of bitumen increases, its fluorescence emission intensity decreases. Therefore non-aged, laboratory aged (rolling thin film oven test (RTFOT) and RTFOT + pressure ageing vessel) bitumen and bitumen extracted from asphalt slabs from a test field after different time periods were investigated. The test field confirmed the connection between intensity and ageing time, further the development of an oxidation gradient over the vertical cross section of the asphalt slabs could be observed. A modified RTFOT was conducted to study the effects of different temperatures and operating times on the fluorescence emission spectrum, as well as the influence of air (containing traces of atmospheric radicals) by conducting the test with nitrogen. Even under nitrogen atmosphere the intensity decreased, which is assigned to internal reactions.

A Phenylselenium-Substituted BODIPY Fluorescent Turn-off Probe for Fluorescence Imaging of Hydrogen Sulfide in Living Cells.

Herein a phenylselenium-substituted BODIPY (1) fluorescent turn-off sensor was developed for the purpose to achieve excellent selectivity and sensitivity for H2S detection based on the substitution reaction of the phenylselenide group at the 3-position with H2S. The excess addition of hydrogen sulfide promoted further substitution of the phenylselenide group at the 5-position of the probe and was accompanied by a further decrease in fluorescence emission intensity. Sensor 1 demonstrated remarkable performance with 49-fold red color fluorescence intensity decrease at longer excitation wavelength, a low detection limit (0.0025 μM), and specific fluorescent response toward H2S over anions, biothiols, and other amino acids in neutral media. It showed no obvious cell toxicity and good membrane permeability, which was well exploited for intracellular H2S detection and imaging through fluorescence microscopy imaging.