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Effect of Laser Quenching on the Microstructure and the Abrasive Wear Resistance of 30KhGSA Steel
摘要： The results of microstructural studies, the microhardness distribution, and the estimation of abrasive wear resistance of structural 30KhGSA steel samples hardened during continuous irradiation with a multichannel (48 beams) CO2 laser are presented. Fine martensite forms in the hardened zone and the steel has a high hardness and abrasion resistance.
关键词： abrasive wear resistance,multichannel CO2 laser,laser quenching,structural steel
更新于2025-09-19 17:13:59
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Role of Emissive and Non‐Emissive Complex Formations in Photoinduced Electron Transfer Reaction of CdTe Quantum Dots
摘要： Bimolecular photoinduced electron transfer (PET) from excited state CdTe quantum dot (QD*) to an electron deficient molecule 2,4-dinitrotoluene (DNT) is studied in toluene. We observed two types of QD-DNT complex formations; (i) non-emissive complex, in which DNT is embedded deep inside the surface polymer layer of QD and (ii) emissive complex, in which DNT molecules are attached to QDs but approach to the QD core is shielded by polymer layer. Because of its non-emissive nature, the lifetime of QD is not affected by dark complex formation, though the steady-state emission is greatly quenched. However, emissive complex formation causes both, lifetime and steady-state emission quenching. In our fitting model, consideration of Poisson distribution of the attached quencher (DNT) molecules at QD surface enables a comprehensive fitting to our time resolved data. QD-DNT complex formation was confirmed by an isothermal titration calorimetry (ITC) study. Fitting to the time resolved data using a stochastic kinetic model shows moderate increase (0.05 ns(cid:2)1 to 0.072 ns(cid:2)1) of intrinsic quenching rate with increasing the QD particle size (from (cid:3) 3.2 nm to (cid:3) 5.2 nm). Our fitting also reveals that the number of DNT molecules attached to a single QD increases from (cid:3) 0.1–0.2 to (cid:3) 1.2–1.7, as the DNT concentration is increased from (cid:3) 1 mm to 17.5 mm. Complex formation at higher quencher concentration assures that the observed PET kinetics is a thermodynamically controlled process where solvent diffusion has no role on it.
关键词： CdTe quantum dot,photo-induced electron transfer,donor-acceptor complex,time-resolved spectroscopy,fluorescence quenching
更新于2025-09-19 17:13:59
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One Pot Aqueous Synthesis of L-Histidine Amino Acid Capped Mn: ZnS Quantum Dots for Dopamine Sensing
摘要： Background: Mn doped ZnS is selected as the right element which is prominent among quantum dot for its high luminescent and quantum yield property and also non toxicity while comparing with other organometallic quantum dot synthesized by using different capping agents. Methods: An interesting observation based on colorimetric sensing of dopamine using manganese doped zinc sulfide quantum dot is discussed in this study. Mn doped ZnS quantum dot surface passivated with capping agents such as L-histidine and also in polymers like chitosan, PVA and PVP were studied and compared. The tunable fluorescence effect was also observed in different polymers and amino acid as capping agents. Optical characterization studies like UV-Visible spectroscopy and PL spectroscopy have been carried out. The functional group modification of Quantum dot has been analyzed using FTIR and size and shape analysis was conducted by using HRTEM image. Results: The strong and broad peak of FTIR in the range of 3500-3300 cm-1 confirms the presence of O-H bond. It is also observed that quenching phenomena in the luminescent peak are due to weaker confinement effect. The average size of the particle is shown to be around 4-5 nm. Changes in color of the quantum dot solution from transparent to dark brown has been due to the interaction with dopamine. Conclusion: Finally, L-Histidine amino acid capped Mn:ZnS shows better results in luminescence and size confinement properties. Hence, it was chosen for dopamine sensing due to its colloidal nature and inborn affinity towards dopamine, a neurotransmitter which is essential for early diagnosis of neural diseases.
关键词： dopamine,Quantum dots,confinement,quenching,fluorescence,amino acid,capping agent
更新于2025-09-19 17:13:59
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Temperature-Dependent Luminescence of Red-Emitting Ba2Y5B5O17: Eu3+ Phosphors with Efficiencies Close to Unity for Near-UV LEDs
摘要： Solid state white light sources based on a near-UV LED chip are gaining more and more attention. This is due to the increasing e?ciency of near-UV-emitting LED chips and wider phosphors selection if compared to devices based on blue LED chips. Here, a brief overview is given of the concepts of generating white light employing near-UV LED and some optical properties of the available phosphors are discussed. Finally, the synthesis and optical properties of very e?cient red-emitting Ba2Y5B5O17:Eu3+ phosphor powder and ceramics is reported and discussed in terms of possible application as a red component in near-UV LED-based white light sources.
关键词： Eu3+,ceramics,near-UV LED,quantum e?ciency,luminous e?cacy,red phosphor,borate,CIE 1931 colour coordinates,thermal quenching
更新于2025-09-19 17:13:59
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Luminescence declining behaviors in YAG:Ce transparent ceramics for high power laser lighting
摘要： High lumen-density laser lighting has become an advanced lighting technology. However, as an important component, transparent light-conversion materials exhibit low efficiency and luminescence declining behaviors, especially under high power density lasers, seriously restricting their potential applications. Herein, high quality YAG:Ce transparent ceramics (TCs) with different Ce concentrations and sizes were designed and fabricated for comparison with YAG:Ce single crystals to reveal the nature behind the above phenomena under the assistance of different encapsulated models of LED/LD devices. The highest luminous efficiency for the TCs of over 248 lm W?1 was achieved in the LED device, while only 170 lm W?1 could be reached for the LD devices. The strong thermal quenching and concentration quenching worked synergistically to result in the luminescence declining behavior in the 0.5 at% YAG:Ce ceramics, which have 80% and 20% responsibility after smart experimental comparison, respectively. Besides, the potential factors for the low efficiency in TC-based LD lighting were also revealed. Therefore, this work not only shows the optical performance of TCs in LED and LD applications, but also presents how the deep influence factors and excitation models lead to differences in their performance. It significantly reinforces the understanding of fundamental problems for TC-based high power laser lighting. These results are crucial for advancing TC-supported technologies in illumination, projection and scintillation.
关键词： transparent ceramics,concentration quenching,laser lighting,YAG:Ce,luminescence declining,thermal quenching
更新于2025-09-16 10:30:52
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Novel Gd3+-doped silica-based optical fiber material for dosimetry in proton therapy
摘要： Optical fibers hold promise for accurate dosimetry in small field proton therapy due to their superior spatial resolution and the lack of significant Cerenkov contamination in proton beams. One known drawback for most scintillation detectors is signal quenching in areas of high linear energy transfer, as is the case in the Bragg peak region of a proton beam. In this study, we investigated the potential of innovative optical fiber bulk materials using the sol-gel technique for dosimetry in proton therapy. This type of glass is made of amorphous silica (SiO2) and is doped with Gd3+ ions and possesses very interesting light emission properties with a luminescence band around 314 nm when exposed to protons. The fibers were manufactured at the University of Lille and tested at the TRIUMF Proton Therapy facility with 8.2–62.9 MeV protons and 2–6 nA of extracted beam current. Dose-rate dependence and quenching were measured and compared to other silica-based fibers also made by sol-gel techniques and doped with Ce3+ and Cu+. The three fibers present strong luminescence in the UV (Gd) or visible (Cu,Ce) under irradiation, with the emission intensities related directly to the proton flux. In addition, the 0.5 mm diameter Gd3+-doped fiber shows superior resolution of the Bragg peak, indicating significantly reduced quenching in comparison to the Ce3+ and Cu+ fibers with a Birks’ constant, kB, of (0.0162 ± 0.0003) cm/MeV in comparison to (0.0333 ± 0.0006) cm/MeV and (0.0352 ± 0.0003) cm/MeV, respectively. To our knowledge, this is the first report of such an interesting kB for a silica-based optical fiber material, showing clearly that this fiber presents lower quenching than common plastic scintillators. This result demonstrates the high potential of this inorganic fiber material for proton therapy dosimetry.
关键词： Bragg peak,dosimetry,Gd3+-doped silica,optical fibers,quenching,sol-gel technique,proton therapy
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Structured Auxiliary Mesh (SAM) Algorithm for Opto-Thermal Simulation of Laser-Based Lighting Systems
摘要： Laser-based lighting systems are an emerging technology, the next step in solid state lighting that revolutionized the way artificial light is generated. The configuration of interest here is the laser-excited remote phosphor (LRP) scheme that consists of a laser diode as the excitation source of an appropriately chosen phosphor sheet. The phosphor is employed for the down-conversion of the incident laser light and broadening of the output spectrum. Although some commercial applications have already been developed, the optimization of LRP systems has yet to be achieved. A bottleneck in their performance is the thermal dependency of the phosphor’s emission characteristics, a phenomenon also known as thermal quenching. As a result, the need for an opto-thermal simulation strategy arises that will enable the study and optimization of LRP systems [1]. The opto-thermal simulation model discussed here is based on Monte Carlo simulations for the optical part, where the absorbed radiant flux is calculated. These optical thermal losses are subsequently used as a volume heat source to solve the transient heat equation by applying the finite element method (FEM) [2]. As thermal quenching is a time-dependent phenomenon in nature, this is an iterative procedure, where the absorbed flux must be calculated for most of the time steps. Typical Monte Carlo ray tracing algorithms use voxel-based meshes to store any calculated properties / attributes. The problem that arises here is that the computational cost for converting the voxel-based mesh to an FEM mesh would be prohibiting for time-dependent analysis. The solution is to directly store the absorbed flux to the FEM mesh. However, the issue that now emerges is locating the interpolating point, namely the point in space where the absorption occurs, within the unstructured FEM mesh. The processing time of a brute force search would be too long, so more sophisticated solutions must be found. SAM algorithms, which were first introduced in [3], are part of a class of algorithms known as geometric search algorithms [4, 5] that deal with point location in unstructured meshes. We propose here a modified SAM algorithm that uses the optical voxel-based mesh as the auxiliary structured mesh for geometric searching. The two meshes, optical and FEM, are superimposed. As point location in voxel-based meshes is trivial, by mapping which elements of the FEM mesh belong to each voxel, we can easily narrow down the number of searches required. To this end, two maps, implemented as binary search trees, are implemented. The first map, maps the voxel number to the nodes of the FEM mesh that lie within it, while the second map, maps the elements of the unstructured mesh that these nodes belong to. The set-up times of these maps heavily depend on the density of the FEM mesh and the order of the elements used. The use of higher-order elements results in considerable set-up times. As higher order elements are not necessary for thermal analysis, this is not a critical issue here. On the other hand, the denser the optical mesh, the fewer FEM elements are mapped to each voxel. However, the size of voxels should be appropriately chosen, since too small voxels may lead to degenerative cases where there are voxels without any nodes lying in them. A distinct advantage of this method is that once the maps are assembled, the search time of elements is O(1). Simulation plays an increasingly crucial role in the study and optimization of optical systems. Due to the increase in computational capabilities, modelling of more complex phenomena can be included and the need of multi-physics approaches rises. The optical properties of materials often shift to temperature above tolerance levels that may render a particular optical design ineffective. In other cases, structural loads may be the critical issue as they can lead to misalignment of optical elements. The proposed SAM algorithm that enables a more efficient coupling of optical and FEM analysis is a valuable tool to such approaches of optical problems.
关键词： Laser-based lighting systems,opto-thermal simulation,Monte Carlo simulations,SAM algorithm,finite element method,thermal quenching
更新于2025-09-16 10:30:52
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Non enzymatic fluorometric determination of glucose by using quenchable g-C3N4 quantum dots
摘要： A non-enzymatic fluorometric assay is described for the determination of glucose. The method is based on the use of g-C3N4 quantum dots (QDs) that have good water solubility. The QDs were synthesized by a one-step solvothermal process using formamide as precursor. The QDs possess an average size of ~5 nm, a band gap of 3.0~3.5 eV, and strong blue fluorescence (with excitation/emission maxima at 400/447 nm). Fluorescence is quenched by glucose (which acts as the electron acceptor) via an electron transfer mechanism. Comprehensive spectroscopy and density functional theory calculations show that the selectivity of the fluorescent probe can be attributed to the presence of N-H bonds that are formed between the QDs (mainly at plane edges) and glucose. The interaction forces lead to the formation of localized states for capturing hot electrons. This results in a decrease in the band gap and a reduction in fluorescence intensity. The probe is selective over some typical interfering species (such as cysteine and albumin) which often are present in the urine of diabetics. The method has a linear response in the 0.2 to 5.0 mM glucose concentration range and a 0.2 mM detection limit.
关键词： Density functional theory calculations,Fluorescent probe,Fluorescence quenching,Inorganic nanomaterials
更新于2025-09-16 10:30:52
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Understanding the excitation wavelength dependent spectral shift and large exciton binding energy of tungsten disulfide quantum dots and its interaction with single-walled carbon nanotubes
摘要： Herein, we investigate the origin of excitation wavelength dependent spectral features and high fluorescence quantum yield in fluorescent 2D tungsten disulfide (WS2) quantum dots (QDs) of average size 2.4 nm. The as-prepared WS2 QDs possess high optical bandgap and reasonably high fluorescence quantum yield ~15.4% in the green region without any functionalization. The broad photoluminescence (PL) spectrum consists of multiple peaks owing to emissions from excitonic transitions and surface defect-related transitions. The excitation wavelength-dependent spectral redshift and narrowing of line shape in the PL peak are analyzed carefully, and it is attributed to the selective excitation/recombination of carriers from different energy levels. The temperature-dependent PL analysis yields an exciton binding energy of ~301 meV in the QDs. Furthermore, we study the interaction between fluorescent WS2 QDs and single-walled carbon nanotubes (SWCNTs) and explore the mechanism of systematic quenching of PL of QDs by SWCNTs. The nature of the Stern–Volmer plot is found to be linear, and the time-resolved fluorescence measurements reveal that the quenching follows primarily the static behavior. Our study further reveals that defect sites in SWCNTs primarily act as the binding sites for WS2 QDs and form non-fluorescent complexes for effective quenching of the PL. The strong interaction between the WS2 QDs and the SWCNTs is evidenced from the spectral shift in the X-ray photoelectron spectroscopy and Raman peaks. Our study reveals the origin of excitation wavelength dependent PL emission from WS2 QDs and the nature of the interaction between WS2 QDs and SWCNTs, which are important for their applications in biomedical imaging and sensing, such as surface-enhanced Raman scattering, etc.
关键词： WS2 quantum dots,Fluorescence quenching,Defects,Carbon nanotubes,Exciton binding energy
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Zhenjiang, China (2019.8.4-2019.8.8)] 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Simulation of Local Laser Annealing of Amorphous TiNiCu Alloy to Create Nanostructured Functional Material
摘要： Present work considers simulation via Comsol Multiphysics software of local laser annealing of amorphous TiNiCu thin ribbon to create a layered nanostructured crystalline-amorphous functional material with the two-way shape memory effect, which is intended for manufacturing of the nanoactuator. Several simulations were performed with different parameters of laser radiation, such as pulse duration and power density. Laser treatment was simplified as a boundary heat source at sample surface.
关键词： liquid,crystalline state,laser treatment,nanotweezers,Comsol Multiphysics,amorphous,state,shape memory effect,quenching
更新于2025-09-16 10:30:52