- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Electric field induced Lyman- <i>α</i> emission of a hydrogen beam for electric field measurements
摘要： Electric field induced Lyman-α emission is a new way of measuring weak electric fields in vacuum and in a plasma. It is based on the emission of Lyman-α radiation (121.6 nm) by a low-energy metastable H atom beam due to Stark-quenching of the 2s level induced by the field. In this paper, we describe the technique in detail. Test measurements have been performed in vacuum between two plates polarized at a controlled voltage. The intensity of emitted radiation, proportional to the square of the field modulus, has been recorded by a lock-in technique, which gives an excellent signal to noise ratio. These measurements provide an in situ calibration that can be used to obtain the absolute value of the electric field. A diagnostic of this type can help to address a long standing challenge in plasma physics, namely, the problem of measuring electric fields without disturbing the equilibrium of the system that is being studied.
关键词： Electric field,hydrogen beam,plasma physics,Stark-quenching,Lyman-α emission
更新于2025-09-10 09:29:36
-
Attachment of a 1,8-Naphthalimide Moiety to a Conjugated Polythiophene Efficiently Improves the Sensing Abilities of Naphthalimide-Based Materials
摘要： A novel polythiophene-based conjugated polymer bearing 1,8-naphthalimide-based pendants is prepared by a two-step modification of regioregular poly[3-(6-bromohexyl)thiophene] involving a nucleophilic substitution reaction of the bromide end-groups with sodium azide followed by a robust, copper-catalyzed Huisgen click reaction with a novel 1,8-naphthalinmide derivative containing an active, N-substituted propyne group. Both the polymer and the highly luminescent-active synthesized dye are extensively studied in solution by UV–vis spectroscopy, photoluminescence, NMR, light-scattering and isothermal titration calorimetry. The materials prepared are considered potential chemosensors for different transition metals, such as Fe2+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+. Luminescence quenching shows that these materials have a higher sensitivity to Fe2+ than to the other metal ions tested. Moreover, the 1,8-naphthalimide-based conjugated polymer is more efficiently quenched by Fe2+ metal ions, at a significantly lower concentration and with a higher binding constant than its parent 1,8-naphthalimide derivative, thus indicating a high potential for sensor development.
关键词： Stern–Volmer constant,polythiophene,1,8-naphthalimide,photoluminescence quenching,conjugated polymers
更新于2025-09-10 09:29:36
-
Enhanced method for determining the low-LET saturation dose of PRESAGE?
摘要： An accurate value for the saturation dose of PRESAGE? is important in elucidating the mechanism of the so-called quenching phenomenon in the 3-D dosimetry of proton beams. This quantity is difficult to obtain, because it involves measuring the optical density of a set of very highly attenuating samples. We present a novel method that makes use of the ability to irradiate microscopically-thin “slices” of a cuvette using microplanar beams from a synchrotron. Using the new method, we were able to measure optical densities of up to 50 cm-1 using a standard spectrophotometer, and we derived a value 14000 Gy for the saturation parameter D37.
关键词： 3-D dosimetry,synchrotron,quenching phenomenon,saturation dose,PRESAGE?,optical density,proton beams,microplanar beams
更新于2025-09-09 09:28:46
-
Probing the Aggregation and Signaling Behavior of Some Twisted 9,9′-Bianthryl Derivatives: Observation of Aggregation-Induced Blue-Shifted Emission
摘要： With an aim to understand the photophysical behavior of twisted organic fluorescent molecules in their aggregated state, two twisted biaryl molecules, namely, 9,9′-bianthryl and 10,10′-dicyano-9,9′-bianthryl, have been synthesized and characterized by conventional spectroscopic methods. To understand the role of C?C bond twisting on the photophysical response of biaryl aggregates, monoaryl counterparts (anthracene and 9-anthracenecarbonitrile) of the biaryl systems are also investigated. Photophysical behaviors of these systems along with their monoaryl counterpart are investigated in both solution and aggregated state. Investigations reveal that fluorescence spectra of the biaryl compounds show blue-shifted emission upon aggregation. Interestingly, no blue shift of the emission has been observed for monoaryl aggregates. Photophysical data of biaryl systems compared to monoaryl unit reveal that change in geometry, during self-assembly process, disfavors the formation of charge-transfer state, which eventually causes blue shift in the emission upon aggregation. In addition to this, potential of these systems toward signaling of nitroaromatic explosive has also been explored. Among all of the nitroaromatics, the highest fluorescence quenching is observed for nitrophenols (say picric acid (PA)). The investigation also reveals that compared to monoaryl systems, biaryl systems are more responsive to fluorescence quenching by nitroaromatics. Perrin’s model of quenching sphere action has been attributed to nitrophenol (PA) selective signaling behavior of biaryl systems.
关键词： aggregation-induced blue-shifted emission,twisted biaryl molecules,fluorescence quenching,photophysical behavior,nitroaromatic explosives
更新于2025-09-09 09:28:46
-
Fully Integrated Active Quenching Circuit Driving Custom-Technology SPADs With 6.2 ns Dead Time
摘要： The minimization of the dead time necessary for the operation of a single-photon avalanche diode (SPAD) plays a crucial role in many demanding single-photon applications. Among these, it is worth mentioning the implementation of airborne light detection and ranging (LIDAR) systems exploited to scan the terrain topography through semiporous obscurations. In this letter, we present the development and the experimental characterization of a fully integrated active quenching circuit (AQC) able to drive custom-technology SPADs with a dead time as low as 6.2 ns, corresponding to a maximum photon count rate of more than 160 Mcps. Thanks to the use of a high-voltage CMOS fabrication technology, the circuit is able to operate also SPADs that require an excess bias of few tens of Volts, like the recently developed red-enhanced SPAD (RE-SPAD), up to a maximum photon count rate of 100 Mcps.
关键词： dead time,Single-photon avalanche diode (SPAD),red-enhanced SPAD (RE-SPAD),active quenching circuit (AQC),single-photon counting (SPC)
更新于2025-09-09 09:28:46
-
An alternative method for correcting fluorescence quenching
摘要： Under high light intensity, phytoplankton protect from bleaching through non-photochemical quenching processes. The consequence of this is suppression of fluorescence emission, which must be corrected when measuring in situ yield with fluorometers. We present data from the Southern Ocean, collected over five austral summers by 19 southern elephant seals tagged with fluorometers. Conventionally, fluorescence data collected during the day (quenched) were corrected using the limit of the mixed layer, assuming that phytoplankton are uniformly mixed from the surface to this depth. However, distinct deep fluorescence maxima were measured in approximately 30 % of the night (unquenched) data. To account for the evidence that chlorophyll is not uniformly mixed in the upper layer, we propose correcting from the limit of the euphotic zone, defined as the depth at which photosynthetically available radiation is ～ 1 % of the surface value. Mixed layer depth exceeded euphotic depth over 80 % of the time. Under these conditions, quenching was corrected from the depth of the remotely derived euphotic zone Zeu, and compared with fluorescence corrected from the depth of the density-derived mixed layer. Deep fluorescence maxima were evident in only 10 % of the day data when correcting from mixed layer depth. This was doubled to 21 % when correcting from Zeu, more closely matching the unquenched (night) data. Furthermore, correcting from Zeu served to conserve non-uniform chlorophyll features found between the 1 % light level and mixed layer depth.
关键词： mixed layer depth,euphotic zone,phytoplankton,Southern Ocean,fluorescence quenching
更新于2025-09-09 09:28:46
-
Optical characterisation of amorphous Se–Te–Sn thin films
摘要： Optical characterization of Sn doped Se–Te thin films has been carried out. The characterization has been carried out using transmission spectra in range 500–2500 nm. Bulk samples were prepared using melt quenching technique and thin films were deposited using thermal evaporation. XRD analysis was used to confirm the amorphous nature of prepared samples. Optical constants such as refractive index and extinction coefficient have been determined using Swanepoel’s method. Variation of refractive index with wavelength has been analysed using single effective oscillator model. Optical band gap of the deposited films was calculated using Tauc plots. The observed properties have been explained using the chemical bond approach.
关键词： Tauc plots,Swanepoel’s method,melt quenching technique,thermal evaporation,Se–Te–Sn thin films,Optical characterization
更新于2025-09-09 09:28:46
-
Impact of activator incorporation on red emitting rods of ZnGa2O4:Cr3+ phosphor
摘要： Chromium doped zinc gallium oxide (ZnGa2O4:Cr3+) microrods were synthesized by simple solid state reaction method. The transformation on crystal structure and optical properties with molar concentration of Cr3+ were analyzed. The cubic spinel nature of ZnGa2O4:Cr3+phosphor and their crystalline nature were con?rmed from x-ray di?ractogram. The average grain size of the samples range between 24 and 29 nm, with lattice parameter values greater than that of bulk. Lattice strain produced in the lattice on doping was estimated from the Williamson–Hall plot. It increases on Cr3+ doping up to 3 mol% and then decreases. Rod like nature of zinc gallate was observed from the surface morphological analysis using SEM. X-ray photoelectron spectroscopy was used for the chemical state identi?cation of the constituent elements in the compound. The photoluminescense spectra consists of various emission lines originated from the chromium ion in the spinel lattice. The purity of red emissions were observed from chromaticity diagram with a concentration quenching initiated from the dipole–dipole interaction, with increase in dopant concentration. Band gap of the samples were estimated using Kubelka-Munk equation which exhibited red shift compared to bulk due to band tailing e?ect.
关键词： Band tailing,Microrods,Cr3+ activator,Quenching
更新于2025-09-09 09:28:46
-
Two Zn(II) coordination polymers based on 5-substituted isophthalic acid: syntheses, crystal structures, luminescence sensing properties
摘要： Two new Zn(II) coordination polymers (CPs), {[Zn(L)(5-nip)]2·5.5H2O}n (1) and {[Zn(L)(5-mip)]·EtOH}n (2) [L = 1,3-bis(benzimidazol-1-yl)-2-propanol, 5-H2nip = 5-nitroisophthalic acid, 5-H2mip = 5-methyisophthalic acid] were solvothermally synthesized and characterized by elemental analyses, IR spectra, thermogravimetric analyses, and single-crystal X-ray diffraction. CP 1 possesses a 1D ladder-like chain structure and further packed into 2D supramolecular architectures by π-π stacking interactions. CP 2 exhibits a 2D 63 layer, which is finally extended into 3D supramolecular network via the weak C–H···O hydrogen bond interactions. CP 1 and CP 2 can be used as luminescent sensors for Hg2+ and Cr2O7 2- ions in water.
关键词： Znic(II),Bis(benzimidazole),Luminescence quenching,Supramolecular architecture,Coordination polymer
更新于2025-09-09 09:28:46
-
Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System
摘要： Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH2) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (KSV ~ 108–1010 M?1) was calculated to be ca. 104 times more for surface quoted NPs in comparison with BSA–NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH2 captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs.
关键词： Bionanosensors,Bovine serum albumin,Luminol,Metal nanoparticles,Energy transfer,Fluorescence quenching
更新于2025-09-09 09:28:46