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Three water-soluble copper complexes based on the amine/pyridine functionalities were investigated, along with quantum dots, as a catalyst–photosensitizer assembly, respectively, for fundamental understanding of photoinduced electron transfer. Luminescence quenching and lifetime measurements were performed to try and establish the actual process that leads to the quenching, such as electron transfer, energy transfer, or complex formation (static quenching). Cyclic voltammetry and dynamic light scattering experiments were also performed. Irrespective of the similar reduction potentials of the three complexes, very different photoluminescence properties were observed. [ABSTRACT FROM AUTHOR]

The influence of Mn2+ ion concentration (x = 0–20 mol%) as well as the role of thermal-annealing temperature (400–600°C) on the structural as well as luminescence properties of NaYF4:Yb, Er (Y: 78-x%, Yb: 20%, Er: 2%) microcrystals prepared via a coprecipitation method is investigated. The cubic phase of the as-prepared NaYF4:Yb, Er (Y: 78%, Yb: 20%, Er: 2%) was found to remain intact upon the addition of the Mn2+ ions, but the thermal-annealing elucidates that the phase of the sample depends upon the annealing temperature as well as the Mn2+ ion concentration. Among the Mn2+ ion co-doped samples, 3 mol% doped samples dominant to have a maximum positive influence on the upconversion luminescence of the sample, and a further increase in concentration leads to the concentration-induced quenching of the upconversion luminescence. Moreover, the enhancement factor of green ( 2 H 11 / 2 → 4 I 15 / 2 a n d 4 S 3 / 2 → 4 I 15 / 2 ), as well as red ( 4 F 9 / 2 → 4 I 15 / 2 ) emission, depend upon the annealing temperature, with a maximum enhancement factor of 5 and 3.12 times for the sample annealed at 400°C, 8.6 and 7.25 times for the sample annealed at 500°C, and 6 and 4 times for the sample annealed at 600°C, as compared to Mn2+ ion undoped samples. The maximum emission strength for the green as well as red is observed for the sample annealed at 600°C and co-doped with 3 mol Mn2+ ions. The laser power-dependent study on all the samples shows that the upconversion process is a multi-photon process, predominantly a two-photon process. [ABSTRACT FROM AUTHOR]

Thermal quenching of luminescence is the most critical problem for rare earth doped phosphors used in light-emitting diodes (LEDs). Herein, we demonstrate that thermal quenching can be considerably suppressed via the negative thermal expansion effect in Zr(WO 4) 2 that serves as host for Eu3+ red emission. The photoluminescence (PL) intensity is surprisingly enhanced by 130% when the temperature is raised from room temperature to 100 °C. As temperature further increases to 160 °C, the PL intensity turns to reduce, which is still 1.4 times of that at room-temperature. Moreover, Zr(WO 4) 2 :15%Eu phosphor has good durability, which still exhibits strong red luminescence (only 13% loss) after being kept in 85 °C/85% relative humidity chamber for 240 h. The anti-thermal quenching of Eu3+ luminescence can be ascribed mainly to the following two factors: first one is the thermal-enhanced energy transfer between Eu3+ ions induced by the contraction of Zr(WO 4) 2 unit-cell volume that leads to the strong structural rigidity of host lattice; second one would be electron traps in the host that favors the increase of electrons on the excited energy levels. This important anti-thermal quenching effect induced from the negative thermal expansion of the host matrix may stimulates a novel and efficient approach to design highly thermal stable phosphors for next-generation LEDs. [ABSTRACT FROM AUTHOR]

At the organic–inorganic interface of nanocrystals, electron‐phonon coupling plays an important but intricate role in determining the diverse properties of nanomaterials. Here, it is reported that highly doping of Yb3+ ions within the nanocrystal host can form an energy‐migration network. The networking state Yb3+ shows both distinct Stark splitting peak ratios and lifetime dynamics, which allows quantitative investigations of quenching and thermal activation of luminescence, as the high‐dimensional spectroscopy signatures can be correlated to the attaching and de‐attaching status of surface molecules. By in‐situ surface characterizations, it is proved that the Yb‐O coordination associated with coordinated water molecules has significantly contributed to this reversible effect. Moreover, using this approach, the prime quencher OH can be switched to CH in the wet‐chemistry annealing process, resulting in the electron‐phonon coupling probability change. This study provides the molecular level insights and dynamics of the surface dark layer of luminescent nanocrystals. [ABSTRACT FROM AUTHOR]

The intensity of defect‐related photoluminescence (PL) in semiconductors changes with temperature, and it usually decreases exponentially above some critical temperature, a process called the PL quenching. Herein, main mechanisms of PL quenching are reviewed. Most examples are given for defects in GaN as the most studied modern semiconductor, which has important applications in technology. Peculiarities of defect‐related PL in I–VII, II–VI, and III–V compounds are also reviewed. Three basic mechanisms of PL quenching are distinguished. Most examples of PL quenching can be explained by the Schön–Klasens mechanism, whereas very few or even no confirmed cases can be found in support of the Seitz–Mott mechanism. Third mechanism, the abrupt and tunable quenching, is common for high‐resistivity semiconductors. Temperature dependence of capture coefficients and a number of other reasons may affect the temperature dependence of PL intensity. The "negative quenching" or a significant rise in PL intensity with temperature is explained by a competition between recombination channels for minority carriers. [ABSTRACT FROM AUTHOR]

Abstract A α-Al 2 O 3 :C,Mg single crystal was investigated by means of optical absorption and photoluminescence measurements aimed at the identification of defects involved in the luminescence process. It was also investigated by thermoluminescence (TL) measurements as a function of the spectral emission in the 1.7–5.0 eV range. Radioluminescence measurements under X-ray excitation as a function of the temperature, from room temperature up to 400 °C were executed. These measurements revealed the presence of F, F-type, F-aggregate, and Mg-perturbed F-type and F-aggregate centers, and their thermal quenching behavior. Further, the role of these defects as recombination centers in the TL process was revealed. [ABSTRACT FROM AUTHOR]

We have previously reported the synthesis, structure and urease inhibitory activity of a complex [Cu2(L)4DMSO2]·2DMSO (HL = (E)-3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)acrylic acid), and we found the complex to show a strong inhibitory activity against jack bean urease [1]. In this study, the interaction of the complex and urease is studied by fluorescence spectroscopy. We find that the fluorescence quenching mechanism of the complex with urease is static quenching. The quenching rate constant (Kq) is 1.6·1012 l/mol·s-1, the quenching constant (Ksv) is 1.6×104 l/mol, the association binding constant (K) is 3.55·104 l/mol, and the binding site number (n) is 1.22. [ABSTRACT FROM AUTHOR]

Dendrimeric rhodamine-derived chemosensor for highly selective determination of Au in aqueous acidic solutions has been developed. The response mechanism is based on the destruction of the dendrimeric molecule to provide fluorescence enhancement via reducing intramolecular quenching. The probe exhibits linear signal response and allows determination of Au content in aqueous solutions from 5 × 10 −8  M. [ABSTRACT FROM AUTHOR]

A new accurate ab initio potential energy surface (PES) of the HeTiO system is constructed. The multi-reference configuration interaction with the Davidson correction is used to obtain the energy points, and the neural network method is employed to fit the PES. State-to-state rotational quenching cross sections and rate coefficients are obtained over a wide range based on the PES. Wigner threshold law is proved to be valid in the ultralow energy regime. In comparison with 3 He, 4 He is more efficient for the TiO molecule cooling process in the dominant transition j  = 1 → 0 due to the isotope effect. [ABSTRACT FROM AUTHOR]

A series of double scheelite-type tungstate green phosphors NaGd(WO 4 ) 2 :Er 3+ , Tb 3+ were synthesized by a hydrothermal route and subsequent calcination process, and they were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometry (EDS), photoluminescence spectroscopy and fluorescence lifetime measurements. The phosphors take on octahedral microcrystals with a mean side length of ~2 μm. In the single doped phosphors system, the energy transfer processes from WO 4 2− to Er 3+ or Tb 3+ were discussed. The quenching concentrations of Er 3+ and Tb 3+ are 0.05 and 0.07, respectively. The critical distances for Er 3+ and Tb 3+ ions are calculated to be 14.28 Å and 12.76 Å, respectively. When doping Er 3+ /Tb 3+ is applied in the single compound, the concentration quenching effect of Tb 3+ ions occurs via a resonant-type dipole-dipole interaction as well as that of Er 3+ ions. Under the excitation with ultraviolet (378 nm) or infrared (980 nm) light, the Er 3+ /Tb 3+ co-doped NaGd(WO 4 ) 2 phosphors emit strong green emission. The obtained samples with bright emission intensity and appropriate decay time are suitable for use as green phosphors in the near ultraviolet LEDs and bioimaging applications. [ABSTRACT FROM AUTHOR]

A Zn 3 L 2 -type metal organic aggregate featuring “six leaf windmill” shaped double cages constructed from a semi-rigid tripodal carboxyl acid ligand H 3 TCPB (1,3,5-tri(4-carboxyphenoxy) benzene) exhibits sensitive luminescent response toward DMA with obvious intensity enhancement and red-shift. During the procedure, the host-gust interaction was supported by single-crystal-to-single-crystal transformation involving drastic conformational change of the molecular host upon μ 2 -bridging H 2 O release and the sensing mechanism was also discussed through theoretical calculations from charge separation hypothesis perspective. The DMA post-modified result of crystal transforming reveals high selective and effective naked eye reversible recognition for Co 2+ ions through the dynamic and static quenching mechanisms. Moreover, the visual luminescent test paper was realized for potential application in concerns of the biology and environment. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQD) are nanosized fragments of graphene with finite band gap. Thus, GQDs show excellent photoluminescence (PL) and also possess good electrochemical properties. In the present study, we synthesized GQDs via hydrothermal (HT) method using Graphene oxide as prepared from improved Hummer's method as a precursor with several modifications. The effect of the variation in the photoluminescence and electrochemical properties of the as-prepared GQDs were studied. Average particle size of the as-synthesized GQDs was roughly 30 nm and produced blue PL on excitation with a wavelength of 365 nm. On reacting the GQDs with Cupric Nitrate and Cobalt Nitrate in separate batches, a significant decrease in the intensity of PL was observed. This quenching of PL of GQDs has been utilized in the qualitative estimation of Metal ion (Cu2+ and Co2+) species in aqueous media. [ABSTRACT FROM AUTHOR]

The quenching of the red Pr 3+ ( 1 D 2 → 3 H 4 ) luminescence in a single crystal of KY(WO 4 ) 2 doped with Pr 3+ is investigated at room temperature under high hydrostatic pressure. The quenching is ascribed to a pressure-induced downshift of the Pr 3+ → W 6+ metal-to-metal charge transfer (or impurity trapped exciton) state. The concomitant decrease of the 1 D 2 → 3 H 4 emission lifetime is reproduced using a phenomenological model. The fitting allows the determination of the pressure-induced shrinkage of the Pr 3+ (Y 3+ )-W 6+ distance in the crystal. The value is consistent with the quantity previously determined in CaWO 4 by means of X-ray diffraction. [ABSTRACT FROM AUTHOR]

The activity concentration of an Y solution was measured by means of a new custom-built 4πβ(LS)-γ coincidence counting system. Efficiency variation was carried out using chemical quenching and neutral density filters. A relative uncertainty of 0.57% was obtained for the activity concentration. Details of the measurements and of the analysis, as well as possibilities to reduce the uncertainty are discussed. Additional validation measurements were carried out by means of the well-established coincidence counting technique using a proportional counter (PC) in the β channel. The results of both coincidence methods were found to be in excellent agreement. [ABSTRACT FROM AUTHOR]

Absorption, fluorescence spectra of chlorophyll a (Chl-a) and all-trans-β-carotene (β-Car) mixing solution are investigated in different polarity and polarizability solvents. The carotenoids regulate the energy flow in photosynthesis by interaction with chlorophyll, leading to an observable reduction of Chl-a fluorescence. The fluorescence red shifts with the increasing solvent polarizability. The energy transfer in the Chl-a and β-Car system is proposed. The electron transfer should be dominant in quenching Chl-a fluorescence rather than the energy transfer in this system. Polar solvent with large polarizability shows high quenching efficiency. When dissolved in carbon tetrachloride, Chl-a presents red shift of absorption and blue shift of fluorescence spectra with increasing β-Car concentration, which implies a Chl-a conformational change. [ABSTRACT FROM AUTHOR]

Dynamical coupling between water and amino acid side-chain residues in solvation dynamics is investigated by selecting residues often used as natural probes, namely tryptophan, tyrosine and histidine, located at different positions on protein surface. Such differently placed residues are found to exhibit different timescales of relaxation. The total solvation response measured by the probe is decomposed in terms of its interactions with (i) protein core, (ii) side-chain and (iii) water. Significant anti cross-correlation among these contributions are observed. When the motion of the protein side-chains is quenched, solvation either becomes faster or slower depending on the location of the probe. [ABSTRACT FROM AUTHOR]

In this study we synthesized a novel graphene-oxide (GO) based CNG repeat hairpin probing system capable of detecting target CAG and CTG DNA repeat sequences. The fluorescence of the 30-mer CNG repeat hairpin structure was quenched dramatically by GO in the absence of the target sequence, with a high quenching constant [ K = 0.030 (mg/mL) −1 ]. We optimized the quenching behavior of this probing system by using graphene oxide (GO) to induce a high degree of discrimination factor (44.6 times) between the fluorescence of the target sequence and that of other non-target sequences. All detection process is explained by displacement mechanism using adsorption, desorption, and hybridization of probe with target DNA sequence on the GO. Graphene-oxide (GO) based CNG repeat hairpin probing system exhibited high sensitivity and selectivity to the target CNG repeat sequence and its detection process is so simple and quick. [ABSTRACT FROM AUTHOR]

Temperature that affects upconversion luminescence (UCL) is important to biological sensing and magnetic imaging. The temperature-dependent UCL of ZnO:Yb3+/Tm3+ nanoparticles (UCNP) was characterized. A detailed analysis of UCL spectra at different annealing temperatures revealed the effects of annealing temperatures, which were determined by using TGA. The blue and the red UCL emissions under NIR 980 nm excitation were greatly enhanced with the increase of annealing temperature from 300 to 780 °C. The change in high-frequency groups (OH− and CO32−) at different annealing temperatures were investigated using IR technique. It was found that the quenching centers were removed due to an increase of annealing temperature. Moreover, for the temperature range of 293 to 338 K, the thermal sensor based on the position shift of the 475 nm wavelength was studied. In addition, relative sensor sensitivity reached a maximum of 2.1% K−1 at 293 K based on the temperature-dependent fluorescence intensity ratio (FIR) of the 700 and 800 nm upconverted emission, which would make the ZnO:Yb3+/Tm3+ nanoparticles a promising candidate for the biological temperature probe. [ABSTRACT FROM AUTHOR]

The crystallization study under non-isothermal conditions of AsTeGa glass was investigated. The studied composition was synthesized by melt-quenching technique and characterized by different techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The XRD analysis revealed that the as-prepared and annealed bulk glass of AsTeGa exhibit the amorphous, and polycrystalline nature, respectively. The DSC results showed that the heating rate affects the characteristic temperatures, for instance, the glass transition, onset, and peak crystallization temperatures. Furthermore, some thermal analysis methods such as the Kissinger and Matusita et al., approximations were employed to determine the crystallization parameters: for example Avrami exponent and the activation energies for glass transition and crystallization process. In addition, we have compared the experimental DSC data with the calculated ones based on the Johnson-Mehl-Avrami (JMA) and Sestak-Berggren SB(M,N) models. The results indicated that the SB(M,N) model is more suitable for describing the non-isothermal crystallization kinetics of the investigated composition. [ABSTRACT FROM AUTHOR]

The Nd-doped lithium-zinc-phosphate glasses were prepared by means of conventional melt quenching method. X-ray diffraction results confirmed the glassy nature of the studied glasses. The physical parameters such as the density, molar volume, ion concentration, polaron radius, inter-ionic distance, field strength and oxygen packing density were calculated using different formulae. The transmittance and reflectance spectra of glasses were recorded in the wavelength range 190-1200 nm. The values of optical band gap and Urbach energy were determined based on Mott-Davis model. The refractive indices for the studied glasses were evaluated from optical band gap values using different methods. The average electronic polarizability of the oxide ions, optical basicity and an interaction parameter were investigated from the calculated values of the refractive index and the optical band gap for the studied glasses. The variations in the different physical and optical properties of glasses with NdO content were discussed in terms of different parameters such as non-bridging oxygen and different concentrations of Nd cation in glass system. [ABSTRACT FROM AUTHOR]

A yellow long persistent luminescence (LPL) phosphor of CaGa2O4:Bi3+ (CGO:Bi) is developed, of which the LPL can be visually recognized (0.32 mcd m−2) over 36 hours after the removal of the excitation source. Furthermore, an excellent LPL performance above the room temperature and unusual thermal quenching behavior are observed. The thermoluminescence (TL) curves indicate that the continuity of the traps structure with different depths is a key factor in ensuring that carriers could be released from deep traps above room temperature successively. The work verifies unambiguously that the continuous defect-state structure is beneficial to the LPL temperature resistant abilities, which would provide a reasonable approach to design new LPL phosphors in extreme environments. [ABSTRACT FROM AUTHOR]

Multicomponent quantitative detection in living samples is becoming increasingly important; however, the current detection strategy may cause fluorescence self-quenching and reduce the sensitivity of detection. To solve the problem, we develop a DNA tetrahedral nanoprobe to control the dyes distance for simultaneous detection of multiple analytes. Compared to mesoporous silica nanoparticles based nanoprobes, the DNA tetrahedral nanoprobes display enhanced fluorescence intensities due to partially avoiding the fluorescence resonance energy transfer. Confocal fluorescence images show that the nanoprobes are capable of detecting and visualizing pH and O2•- in living cells under a single wavelength excitation. In an inflammation model for mice, the nanoprobes simultaneously image the down-regulation of pH and up-regulation of O2•-. We expect that the current strategy can provide new opportunities in designing probes for multiplexed detection with reduced self-quenching and enhanced sensitivity. [ABSTRACT FROM AUTHOR]

A 3D network with the (4²·6·8³) topology of metal-organic framework possessing an open 1D channel was synthesized by rigid and planar tetracarboxylic acid 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid (H4L). The luminescent properties of 1 shows highly sensitive response to nitrobenzene, Fe3+ and CrO4 2- through luminescence quenching effects, making it a promising luminescent sensor for nitro aromatic compounds, Fe3+ and CrO4 2-. [ABSTRACT FROM AUTHOR]

Organic dye lasers are widely used in science and technology. Impregnation of dyes into polymers demonstrates many technical advantages, especially in the case when the dye monomer solution is filled inside the cavities of nanoporous glasses and then polymerized within the pores (PFNPG-P composite). This allows to create a rigid true solid-state active elements. Peculiarities of luminescence in such compositions are the subject of the work. Luminescence of 12 laser dyes was studied in liquid solutions (ethanol, MMA) and solid matrixes such as PMMA and PFNPG-P composite. Concentration dependences were measured for pyrromethenes, phenalemines, xanthenes and other types of dyes to define the quenching threshold of luminescence. [ABSTRACT FROM AUTHOR]

A single-band near-infrared (NIR) quantum cutting (QC) is efficiently achieved for 1190 nm fluorescence by structuring Ho 3+ -Yb 3+ couple as energy clustering in KLu 2 F 7 host under excitation of ultraviolet-to-green photons. In comparison with Ho 3+ singly doping, the intensity of NIR emission was enhanced by at least 5 times as 75%Yb 3+ is codoped into KLu 2 F 7 :Ho 3+ . On the basis of experimental data and theoretical analysis, the formation of Yb 3+ (fractional Ho 3+ ) energy clustering at sub-lattice level is demonstrated to account for resonant energy transfer (ET) of Ho 3+ → Yb 3+ , back ET of Yb 3+ : 2 F 5/2 → Ho 3+ : 5 I 6 , and the crucial energy preserving by confining Yb 3+ energy migration. By mean of steady and dynamic spectroscopies, an internal quantum yield for the single-band 1190 nm emission is appropriately evaluated to be more than 190% for K(Lu 0.24 Ho 0.01 Yb 0.75 ) 2 F 7 without any obvious concentration quenching. This nanostructured design of single-band NIR QC will open up novel available way to get efficient NIR emitters, which can boost the promising applications of solar cells, optical communication, short-wavelength infrared (SWIR) bio-imaging in vivo , etc. [ABSTRACT FROM AUTHOR]

Ultrafast bimolecular photoinduced electron transfer (PET) between six coumarin dyes and four viologen molecules in the stern layer of sodium dodecyl sulfate micelle have been studied using femtosecond broadband transient absorption spectroscopy and femtosecond fluorescence up-conversion spectroscopy over a broad reaction exergonicity (ΔG0). Emanating the formation of radical cation intermediates of viologen molecules using the transient absorption and the fast decay component of coumarins using the fluorescence up-conversion studies the forward bimolecular electron transfer rate (ket) have been measured with high accuracy. The relationship of ket with ΔG0 found to follow a Marcus type bell-shaped dependence with an inversion at -1.10 eV. In this report, we have studied PET reaction using ultrafast spectroscopy at the quencher concentration where static quenching regime prevails. Moreover, the incompetency of Stern-Volmer experiments in studying ultrafast PET has been revealed. In contrary to previous claims, here we found that the ket is lower for lower lifetime coumarins, indicating that static, nonstationary and stationary regime of quenching have the minimal role to play to in the bimolecular electron transfer process. By far, this report is believed to be the most efficient and immaculate way of approaching Marcus inverted region problem in the case of bimolecular PET and settles the long-lasting debate of whether the same can be observed in micellar systems. [ABSTRACT FROM AUTHOR]

ABSTRACT Nonconventional luminogens without classic conjugated structures have drawn increasing interests owing to their fundamental importance and promising applications. These luminogens generally bear such subgroups as tertiary amine, C = C, C≡N, C = O, OH, ether, and imide. The emission mechanism, however, remains under debate. Different assumptions like oxidation or acidification of tertiary amines, aggregation of C = O groups, as well as clustering and electron cloud overlap are proposed. Unlike concentration quenching and aggregation-caused quenching (ACQ) that are normally observed in traditional luminogens, many of these unorthodox luminogens exhibit unique aggregation-induced emission (AIE) characteristics, regardless of their molecular architectures. This review summarizes varying unorthodox luminogens with AIE features, aiming to outline the recent advances in this exciting area, with focus on the macromolecular systems. In light of the reported results, clustering-triggered emission mechanism, namely clustering of diverse subgroups with subsequent electron cloud overlap and conformation rigidification can well rationalize the photophysical behaviors of most systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 560-574 [ABSTRACT FROM AUTHOR]

Chemosensor C1 , namely, 3-acetoacetyl-7-hydroxycoumarin, was synthesized and exhibited highly selective and sensitive fluorescence sensing ability for Cu 2+ over other metal ions under physiological conditions. The fluorescence quenching response of C1 for Cu 2+ indicated that C1 can be used as an on-off fluorescent chemosensor to selectively detect Cu 2+ . The binding process was confirmed by UV–vis absorption, fluorescence measurement, mass spectroscopy, IR spectra and DFT calculation. To test the practical use of the probe, the determination of Cu 2+ in real water samples was evaluated. The application of the fluorescent probe in monitoring intracellular Cu 2+ in HeLa cells has also been demonstrated. [ABSTRACT FROM AUTHOR]

The determination of captopril was performed by measuring the photoluminescence quenching of pH sensitive mercaptopropanoic acid capped CdTe quantum dots. Under optimum conditions, the calibration model (log F/F as a function of the concentration of captopril) was linear up to 8 × 10 mol/L (1.7 μg/mL) and the limit of detection (x - 3s) was 2.7 × 10 mol/L (18 ng/mL). A possible mechanism for quenching is proposed. The method was applied in the determination of captopril in two commercial pharmaceutical formulations, indicating that it can be used for simple and fast quantitative control of commercial medicines or pharmaceutical preparations. [ABSTRACT FROM AUTHOR]

In order to better understand the compositional and structural complexity of dissolved organic matter (DOM) macromolecules and provide mechanistic information on the binding of hydrophobic organic contaminants (HOCs) to DOM, we fractionated large amounts of lake water into three hydrophobic DOM-fractions. The variation of the partitioning coefficients ( K ) of pyrene at different pH levels was examined by florescence quenching titration. Results show that, relative to the more polar acidic DOM-fractions, the hydrophobic neutral fraction exhibits a higher sorption ability to pyrene. Generally, the sorption of pyrene to the three hydrophobic fractions is strongly pH-dependent. The K values of pyrene generally increase with decreasing pH levels, which is especially obvious in the sorption of pyrene to the fulvic acid fractions, suggesting that the binding is controlled by hydrophobic interactions. The mechanisms underlying the binding of pyrene to the hydrophobic fractions were also discussed. Our data are beneficial to further understanding the binding of HOCs to DOM and how it has been affected, which may result in more accurate predictions of K . [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and emission properties of 2-coordinate dicopper(i) complexes bearing two trimethylene-bridged bis-NHC ligands, [Cu2(L3Me)2](PF6)2 (1), [Cu2(L3Et)2](PF6)2 (2), [Cu2(L3Bu)2](PF6)2 (3), [Cu2(L3MeOPh)2](PF6)2 (4) and [Cu2(L3Mes)2](PF6)2 (5), where L3R denotes trimethylene-bridged bis(N-heterocyclic)carbene (NHC) ligand substituted by two R groups at the nitrogen atoms of NHC, have been investigated. The quantum yield, Φ, and the lifetime, τ, of the emission of 2, are 0.21 and 25 μs, respectively in methanol, which is a well-known solvent for quenching the luminescence of many copper(i) complexes. The 8-shaped geometry of the dicopper(i) complexes brings a considerable copper(i)–copper(i) interaction which affects the luminescent properties. Additionally, we find that methoxyphenyl and mesityl groups substituted at the nitrogen atom of the NHC moiety drastically stabilize the bis(NHC) copper(i) complexes even in air-saturated acetone-d6. [ABSTRACT FROM AUTHOR]

Plasma electrolytic saturation (PES) technique which holds the advantages of short treating time and limited heating influence and immediate quenching effect is conducted under high voltage power supply in some electrolyte has been extensively applied to enhance the surface performance of metallic materials. Steel is widely used in various fields thanks to its promising merits of easy workability, plasticity, toughness and weldability. It accounts for a large proportion in the application scope of the metal materials. Steel surfaces with good corrosion resistance, promising wear resistance and high hardness would be obtained by PES. Meanwhile, uniformed coatings can be formed without special requirements for substrate geometries using the PES. This paper first presents a brief introduction of the technological principle of PES. The status on studies and applications of PES for improving surface performance of steels has been reviewed. [ABSTRACT FROM AUTHOR]

[Display omitted] • TWGCe glasses show amorphous nature and are free from impurities and bubbles. • TWGCe glasses enhance optical properties of Ce3+ by reducing non-radiative losses. • Exhibit deep-blue luminescence through Ce3+: 5 d → 4 f transition when excited at 323 nm. • They are favourable as blue light sources in the design of phosphor-based white LEDs. Different concentrations of Ce3+-doped TeO 2 -WO 3 -GeO 2 -Ce 2 O 3 (TWGCe) glasses were prepared by melt-quenching method and characterized. Different spectroscopic and luminescence properties were evaluated using room temperature absorption and emission spectra. The absence of sharp X-ray diffraction peaks and the presence of broad band from 18° to 35° shows the amorphous phase of studied glasses. The Fourier transform infrared absorption spectra show the presence of various vibrational bonds. The optical properties of TWGCe glasses were studied by exciting the glass samples at 323 nm ultraviolet wavelength. The quenching in luminescence is noticed at × = 0.5 mol% along with a red-shift at higher Ce3+ concentrations. The decay time was found decrease with increase of concentration of Ce3+ ions. These glasses emit intense blue luminescence with CIE coordinates (0.161, 0.018) when excited at 323 nm radiation. These glasses are favourable as blue light sources in the design of phosphor-based white LEDs. [ABSTRACT FROM AUTHOR]

The physical, structural, and luminescence properties of lithium aluminum borate glasses as a function of Gd 2 O 3 and Eu 2 O 3 concentration were reported. The glasses composition of 25Li 2 O–5Al 2 O 3 -YGd 2 O 3 -(70-Y-Z)B 2 O 3 -ZEu 2 O 3 system was successfully synthesized through a conventional melt-quenching technique. The various Gd 2 O 3 concentration, 2.5 mol% is suitably added into the host composite, supporting by X-ray induced luminescence and photoluminescence analysis. The influence of the Eu 2 O 3 concentration doped glasses system has been investigated in different concentrations of Eu3+ ions. It was found that the emission intensity increase with an increase of Eu 2 O 3 concentration up to 3.0 mol% (luminescence quenching. The maximum intensity peaks were located at 614 nm (red emission), which was due to 5 D 0 →7 F 2 transitions of Eu3+ ions. The decay profile is measured to prove the occurrence of maximum energy transfer efficiency (Eu3+-Eu3+) obtained is as high as 15.36% for their potential candidature in solid state device applications. [Display omitted] • Glass systems in the 25Li 2 O–5Al 2 O 3 -YGd 2 O 3 -(70-Y-Z)B 2 O 3 -ZEu 2 O seriewere prepared. • The photo and X-ray luminescence spectra show optimum concentration at 2.5 mol% of Gd 2 O 3. • The XANES) confirmed Eu atom remains a trivalent oxidation state. • The I–H model indicates energy transfer between Eu3+- Eu3+ ions occur inelectric dipole-dipole. • Calculated energy transfer efficiency value is 15.36% of the Eu3+. [ABSTRACT FROM AUTHOR]

Differentiation of biologically important thiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) is still a challenging task. Herein, we present a novel fluorescent chemodosimeter capable of selectively detecting Cys over other biothiols including Hcy and GSH and other amino acids by a facile thiol-Michael addition/transcyclization rearrangement cascade click process. The unique transcyclization step is critical for the selectivity as a result of the kinetically favorable formation of a six-membered ring with the Cys Michael adduct. Moreover, the probe adopts a distinctive dual quenching mechanism-photoinduced electron transfer (PET) and photoinduced intramolecular charge transfer (ICT) to deliver a drastic turn-on fluorescence response only at the Cys-selective transcylization step. The judicious selection of strong electron-withdrawing naphthalimide fluorophore with maleimide group enhances the electrophilicity and thus reactivity for the cascade process leading to fast detection and ultrasensitivity with a detection limit of 2.0 n m ( S/ N=3). The probe has demonstrated its practical utility potential in Cys imaging in live cells. [ABSTRACT FROM AUTHOR]

Partitioning of light energy into several pathways and its relation to photosynthesis were examined in a shade-demanding species Panax notoginseng (Burkill) F.H.Chen ex C.Y.Wu & K.M.Feng grown along a light gradient. In fully light-induced leaves, the actual efficiency of PSII photochemistry (ΔF/Fm'), electron transport rate (ETR), non-photochemical quenching (NPQ) and photochemical quenching (qP) were lower in low-light-grown plants; this was also the case in fully dark-adapted leaves under a simulated sunfleck. In response to varied light intensity, high-light-grown plants showed greater quantum yields of light-dependent non-photochemical quenching (ΦNPQ) and PSII photochemistry (ΦPSII) and smaller quantum yields of fluorescence and constitutive thermal dissipation (Φf,d). Under the simulated sunfleck, high-light-grown plants showed greater ΦPSII and smaller Φf,d. There were positive relationships between net photosynthesis (Anet) and ΦNPQ+f,d and negative relationships between Anet and ΦPSII in fully light-induced leaves; negative correlations of Anet with ΦNPQ+f,d and positive correlations of Anet with ΦPSII were observed in fully dark-adapted leaves. In addition, more nitrogen was partitioned to light-harvesting components in low-light-grown plants, whereas leaf morphology and anatomy facilitate reducing light capture in high-light-grown plants. The pool of xanthophyll pigments and the de-epoxidation state was greater in high-light-grown plants. Antioxidant defence was elevated by increased growth irradiance. Overall, the evidences from P. notoginseng suggest that in high-light-grown shade-demanding plants irradiated by high light more electrons were consumed by non-net carboxylative processes that activate the component of NPQ, that low-light-grown plants correspondingly protect the photosynthetic apparatus against photodamage by reducing the efficiency of PSII photochemistry under high light illumination, and that during the photosynthetic induction, the ΔpH-dependent (qE) component of NPQ might dominate photoprotection, but the NPQ also depresses the enhancement of photosynthesis via competition for light energy. [ABSTRACT FROM AUTHOR]

Graphene has attracted considerable attention in multidisciplinary research fields and shown various promising applications due to its unique structure and extraordinary physicochemical properties. This review covers the latest advances in graphene materials-based chemiluminescence (CL) for sensing. Chemiluminescence resonance energy transfer and luminescence quenching of graphene materials are discussed. Graphene materials, such as graphene nanosheets, graphene quantum dots, graphene oxide, and reduced graphene oxide have been employed successfully in CL systems in recent years. Graphene materials can be utilized as catalysts, platforms, and energy acceptors to improve the performance of CL. Possible challenges and future perspective on this topic are also presented. [ABSTRACT FROM AUTHOR]

Evolution of crystalline structure caused by heat treatment and its influence on magnetic properties of two melt-spun Hf 2 Co 11 B alloys in fully amorphous and partially crystalline states have been investigated. The as-cast ribbons were annealed in order to improve the hard magnetic properties by inducing the formation of nanocrystalline phases with high anisotropy. The X-ray diffraction and magnetic measurements confirmed the coexistence of two Hf 2 Co 11 phases, crystallizing in different structures, with the rhombohedral one showing hard magnetic properties. Annealing of fully amorphous alloy resulted in the lower coercive field in comparison to that of annealed partially crystalline ribbon. From the point of view of exchange coupling between magnetic phases and magnetic hardening, the optimum annealing temperature and time were determined to be 570 °C and 60 min, for partially crystalline sample. Annealing at 650 °C for 1 h leads to excess of the HfCo 3 B 2 phase above the critical value and results in a decrease in the coercive field. Isothermal annealing increases the magnetocrystalline anisotropy constant K 1 from 7.52 for the as-quenched sample to 12.11 Merg/cm 3 for the partially crystalline ribbon. The existence of quenched-in nanocrystals resulted in higher coercive fields, up to 3.23 kOe, after annealing. [ABSTRACT FROM AUTHOR]

Eu 3+ ions doped boro-phosphate glasses containing Ag nanoparticles have been prepared by following the conventional melt quenching technique. The structural and optical properties were explored through recording XRD, FTIR, HR-TEM, absorption, emission and decay measurements. The presence of spherical Ag nanoparticles in the present glasses was confirmed through TEM analysis. The bonding nature of the Eu 3+ ions with its surrounding ligands was explored from the absorption spectra. The luminescent intensity of the emission transitions correspond to the Eu 3+ ions were found increase to while increasing the Ag content upto 0.5 wt% due to the surface plasmon resonance and further increase in Ag content leads to luminescence quenching. Judd–Ofelt (JO) parameters, radiative properties were calculated from the emission spectra and further characterized through CIE 1931 color chromaticity diagram to examine the suitability of the present glasses for laser applications. The decay curves exhibit single exponential behavior for all the title glasses and the experimental lifetime values were obtained from curve fitting method and the results were discussed in the present work. [ABSTRACT FROM AUTHOR]

Quenching of Ru(bpy)32+ electrochemiluminescence (ECL) by Cl−, Br−, and I− ions was studied as a function of halide concentration in a bipolar electrochemical cell. All of the halides investigated showed similar qualitative behavior: above a critical concentration, ECL intensity was found to decrease linearly as the halide ion concentration was increased, due to dynamic quenching of Ru(bpy)32+ ECL. Stern-Volmer slopes (KSV) of 0.111±0.003, 4.2±0.3, and 6.2±0.3 mM−1 were measured for Cl−, Br− and I−, respectively. The magnitude of KSV correlates with halide ion oxidation potential, consistent with an electron transfer quenching mechanism. Using the bipolar platform described herein, aqueous, halide-containing solutions could be quantified rapidly using the sequential standard addition method. The lower detection limit is determined by a complex mechanism involving the competitive electrooxidation of halide ions and the ECL co-reactants, as well as the passivation of the surface of the bipolar electrode, and was found to be 0.20±0.01, 0.08±0.01 and 10±1 mM, respectively, for I−, Br−, and Cl−. The performance of the bipolar ECL quenching assay is comparable to previously published fluorescence quenching methods for the determination of halide ions, while being much simpler and less expensive to implement. [ABSTRACT FROM AUTHOR]

A novel [Ru(bpy) 2 (atatp)] 2 + (bpy = 2,2′-bipyridine and atatp = acenaphtheno[1,2- b ]-1,4,8,9-tetraazatriphenylene) can induce the condensation of herring sperm DNA to form an orange-red cast film via intercalation and electrostatic attraction. The thus-prepared cast film shows microsecond emission lifetimes and reversible luminescence tuning characteristics by oxygen and nitrogen with an on–off emission intensity ratio of 4.3. The photoluminescence of [Ru(bpy) 2 (atatp)] 2 + bound to a DNA condensed matrix can be quenched by water, dissolved oxygen, copper(II) and ferrocyanide ions. The DNA binding is found to hardly alter the dynamic quenching of [Ru(bpy) 2 (atatp)] 2 + by oxygen at a low DNA-to-Ru(II) molar ratio ( r = 0.83), allowing [Ru(bpy) 2 (atatp)] 2 + to keep a basically unchanged oxygen quenching constant, as well as endow the photo-induced electron transfer between [Ru(bpy) 2 (atatp)] 2 + and copper(II) cations, and weaken the electrostatic attraction of [Ru(bpy) 2 (atatp)] 2 + with ferrocyanide anions. In addition, the DNA condensation induced by [Ru(bpy) 2 (atatp)] 2 + can protect the DNA oxidative damage against superoxide anion and hydroxyl radical toxicity. The present results could provide a versatile platform for better fabrication of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Efficient and stable quenching of electrochemiluminescence (ECL) of tris(2,2’-bipyridine)-ruthenium(II) (Ru(bpy) 3 2+ )/tri-n-propylamine (TPrA) system by graphene oxide (GO) at the glassy carbon electrode (GCE) was reported. For figuring out the possible reasons of the quenching mechanism, the electrochemical and ECL performance of GO, different reduction degree of reduced graphene oxide (RGOs) and polymer wrapped GO modified GCEs were systematacially investigated. The results demonstrated that the oxygen-containing groups and poor electrical conductivity of GO, along with the distance between GO and Ru(bpy) 3 2+ was suggested as the reasons for quenching ECL. On the basis of this essential quenching mechanism, a novel “signal on” ECL DNA biosensor for ultrasensitive detection of specific DNA sequence was constructed by self-assembling the ECL probe of thiolated shared-stem hairpin DNA (SH-DNA) tagged with Ru complex (Ru(bpy) 3 2+ derivatives) on the surface of GO/gold nanoparticles (AuNPs) modified GCE. The ECL probe sequences have their ECL signal efficiently quenched when they are self-assembled on the surface of GO unless they hybridizes with their target DNA (t-DNA) sequence. The designed ECL biosensor exhibited excellent stability and reproducibility, outstanding selectivity, and an extremely sensitive response to t-DNA in a wide linear range of 100 aM–10 pM with a low detection limit of 65 aM. Our findings and the design of biosensing switch would open a new avenue in the application of GO based ECL quenching strategy for ultrasensitive bioassays. [ABSTRACT FROM AUTHOR]

The spectroscopic and structural characteristics of various concentrations of Sm 2 O 3 doped strontium lead zinc phospho-tellurite glasses with molar composition x % Sm 2 O 3 + 5SrO + (15- x) PbO + 20 ZnO + 50 P 2 O 5 + 10 TeO 2 (where x = 0.25, 0.5, 0.75, 1 mol%) have been reported here. The XRD and FTIR measurements are performed to explore the structural characteristics of the glasses. The absorption spectra reveal that the bands at 400 nm and 1220 nm are highly intense in comparison to others. The Judd-Ofelt intensity parameters Ω λ (λ = 2, 4, 6) have been evaluated from the absorption and thereby the radiative and lasing parameters are estimated. The most intense excitation band around 400 nm is opted as the excitation wavelength to study luminescence properties. Luminescence spectra exhibit the most intense emission band at 598 nm pertaining to 4G 5/2 → 6H 7/2 transition which is responsible for reddish-orange colour origination. We have measured the experimental lifetime of the 4G 5/2 excited state by the suitable fittings of the decay curves. Luminescence concentration quenching (x > 0.75%) and the reduction of decay lifetimes have been observed owing to enhancement of non-radiative energy losses through the cross-relaxation channels. The higher values of quantum efficiency and stimulated emission cross-section promote the lasing action of the present glasses. The location of CIE chromaticity coordinates recommends that these glasses could be utilized as reddish-orange color emitting laser materials. [Display omitted] • Luminescence properties of Sm3+ doped SrO–PbO–ZnO–P 2 O 5 –TeO 2 glasses are explored. • XRD, FTIR, absorption, JO, luminescence, decay curve and CIE diagram are analyzed. • Concentration quenching has been observed beyond 0.75 mol% doping of Sm3+ ions. • 0.75Sm glass emits high reddish-orange (598 nm, 4G 5/2. → 6H 7/2) with color purity 93%. • Radiative and laser parameters show that the glass is suitable for visible laser. [ABSTRACT FROM AUTHOR]

The optical properties of Dy3+ in barium borate (BaB) glass are compared to those of Dy3+ in lithium aluminoborate (LiAlB) glass. Sample series with varying modifier-to-former ratio and different Dy3+ concentration are analyzed for their optical absorption, external quantum efficiency, luminescence yield, and chromaticity. The photoluminescence (PL) spectra are dominated by two emission bands in the visible spectral range, namely at 483 nm and 575 nm. The BaB as well as the LiAlB glass series show a luminescence quenching upon increasing the Dy3+ concentration, though the optical absorption increases linearly. For both, a change in the modifier-to-former ratio from 1 : 2 to 1 : 4 leads to an increase in luminescence yield with the maximum at a Dy3+ content of (0.2–0.3) at.%. Compared to LiAlB glass, the absorption coefficient as well as the PL quantum efficiency of Dy3+ are slightly lower in BaB glass. The colour impression of the BaB and the LiAlB glass series are very similar; it changes with the modifier-to-former ratio as well as the Dy3+ concentration. The analysis of the PL lifetime measurements on the basis of the Förster model yield an intrinsic Dy3+ lifetime of slightly above 900 μs. For a Dy3+ content of 0.5 at.%. and higher, the energy transfer between neighbouring Dy3+ ions is noticably enhanced. • Optical properties of Dy3+ in LiAlB glass are better than those in BaB glass. • Dy3+ absorption coefficient increases linearly with increasing doping level. • Highest quantum efficiency is achieved at a Dy3+ content of 0.1 at.%. • Photoluminescence quenching occurs at a Dy3+ content of (0.2–0.3) at.%. • Colour impression shifts to yellowish on increasing network former and Dy3+ content. [ABSTRACT FROM AUTHOR]

Al + Fe 2 O 3 + BaO 2 and NaNO 3 as the reactive system and the foaming agent, respectively, are used to prepare barium ferrite hollow microspheres (BFHMs) by self-reactive quenching technology based on flame spraying technology, self-propagating high-temperature synthesis (SHS) technology and quick chilling technology. Effects of NaNO 3 on the particle size, morphology, phase structure and microwave absorption properties of BFHMs are investigated through SEM, XRD, particle size analyzer, high-speed camera and vector network analyzer. The results show that, after adding 10 wt.% NaNO 3 , the average particle size of BFHMs decreases initially from 28 μm to 6 μm, as well as the particle distribution gets narrower. Micro-nano lamellar crystals appear on the surface of BFHMs, with the dimension ranging from 500 nm to 2 μm. BaFe 2 O 4 and Fe 3 O 4 , which have spinel structures, can be seen in XRD, and they are beneficial for microwave absorption properties. The real part ( ɛ ′), imaginary part ( ɛ ″) of permittivity, and the imaginary part of permeability ( μ ″) increases in 0.5–18 GHz. The real part ( μ ′) of permeability increases in 0.5–10.3 GHz, while decreases in 10.3–18 GHz. The microwave absorption properties are improved greatly, and the minimum reflectivity decreases from −3.1 dB to −9.8 dB. The reasons for improvement of microwave absorption properties after adding NaNO 3 foaming agent may be the decreasing of the particle size of BFHMs, the appearance of ferrites (BaFe 2 O 4 and Fe 3 O 4 ) with spinel structure and special micro-nano tabular crystals. Magnetoplumbite-type barium ferrites (BaFe 12 O 19 ) hollow microspheres are obtained after heat-treatment and the microwave absorption properties are further improved. [ABSTRACT FROM AUTHOR]

Gd 2−x Eu x O 3 nanophosphor with enhanced luminescence has been synthesized by solution combustion method in diethylene glycol medium. The effect of Eu 3+ content on the structure, morphology and luminescence dynamics has been investigated. The observed red shift in charge transfer band of the nanophosphor with increase in Eu 3+ content is attributed to the increase in covalency and Eu–O bond length. Excess europium content leads to reduction in intensity of photoemission as a result of concentration quenching. Transient characteristics exhibit single exponential behaviour and the fitted life time values get shortened with increase of Eu 3+ content, due to increase in non-radiative transition rate. The observed quenching of luminescence in the phosphor is found to be in agreement with the energy transfer theory proposed by Dexter and Schulman and found that dipole–dipole interaction between Eu 3+ ions is the key mechanism responsible for quenching. Critical energy transfer distance between Eu 3+ ions in Gd 2−x Eu x O 3 is determined to be 1.148 nm. Judd–Ofelt intensity parameters and the radiative parameters of the phosphors were evaluated from the emission spectrum to analyse the crystal field environment and the degree of covalency between the rare-earth ion and the surrounding ligands. The value of Ω 2 intensity parameter confirmed the hypersensitive nature of the 5 D 0 – 7 F 2 transition with larger asymmetry around Eu 3+ ions. [ABSTRACT FROM AUTHOR]

Heat transfer characteristics of intact fuel pins under reflood conditions have been extensively studied to understand the quench behavior of a typical pressurized water reactor (PWR). Overheating of fuel pins due to loss of nucleate boiling under exposed conditions causes the clad to balloon over large portions of the fuel pin length (up to 60%). The reflood behavior of ballooned fuel pins has been studied experimentally for ballooned heater pin configurations with up to 15% ballooned length of the total length. Substantial changes in the reflood behavior are observed for a higher extent of the ballooned region. An experimental setup is thus being developed to study the effect of the large extent of the ballooned region (up to 60% of the total length) on the reflood behavior. The experimental setup employs a 5 x 5 matrix of indirectly heated fuel pins surrounded by 32 dummy fuel pins. The scaling analysis carried out for the design of the experimental setup is presented here. The nondimensional n terms pertaining to the quench phenomena have been conserved as compared to the typical PWR values. The evolution of some of the nondimensional n terms under reflood conditions has been discussed for simulations done with RELAP5 for ballooned as well as nonballooned test cases. Delayed quenching is observed in the extended ballooned fuel pins due to poor heat transfer in the ballooned region. [ABSTRACT FROM AUTHOR]

Novel amorphous carbon nanoparticles (ACNPs) with high electrochemiluminescence (ECL) quenching efficiency were prepared from candle soot with a quite simple approach. The prepared ACNPs were employed as novel energy quenchers for an ECL immunosensor on a disposable screen-printed carbon electrode array (SPCEA) substrate. Gold nanoparticles-doped chitosan composite film was utilized to immobilize Ru(bpy) 3 2+ -labeled antibody on the SPCEA, and ACNPs were linked with antigens to obtain ACNP-antigen conjugate. The immunoreaction between the Ru(bpy) 3 2+ -labeled antibody and the ACNP-antigen conjugate bridged the Ru(bpy) 3 2+ donor and the ACNPs acceptor, which led to quenching of ECL emission from Ru(bpy) 3 2+ via energy transfer. In the presence of the target antigen, this antigen competed with the ACNP-antigen for the immobilized Ru(bpy) 3 2+ -labeled antibody, thus led to decreased occurrence of the ECL quenching. This ACNPs-based ECL quenching system was successfully applied to detect mouse IgG, which was used as a model analyte. The method showed a linear range of 0.50–400 ng mL −1 and a detection limit of 0.35 ng mL −1 . The results for real sample assay and recovery test demonstrated the reliability of this ECL quenching-based immunosensor. It could be further extended to multiplexed immunoassay of biomarker proteins for clinical diagnosis. [ABSTRACT FROM AUTHOR]