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Methodical engineering of defects in MnXZn1-X O(x?=?0.03, and 0.05) nanostructures by electron beam for nonlinear optical applications: A new insight
摘要： A series of MnxZn1-xO (x = 0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in e-beam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters.
关键词： Mn:ZnO nanostructures,8MeV e-beam,Spatial confinement effects,Defects quenching,Third harmonic generation
更新于2025-09-19 17:15:36
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Microstructure refinement and properties of 1.0C-1.5Cr steel in a duplex treatment combining double quenching and laser surface quenching
摘要： The 1.0C-1.5Cr steel was subjected to conventional quenching and laser surface quenching treatment. A process combing double quenching and laser surface quenching was proposed for enhancing surface hardness and obtaining finer microstructure. The cementite dissolution and grain growth behavior in the austenitizing process of single quenching, double quenching, and laser surface quenching were studied. The results indicated that compared with single quenching, mean diameter of undissolved cementite particles (UCP) was much finer in double quenching, and the final prior austenite grain size (PAGS) could be decreased by nearly 40% to about 4.5 μm. Both grain and cementite particles near the surface will coarsen after laser surface treatment. Compared with single quenching, the PAGS within hardened layer can be decreased by at least 11% through double quenching, and the mean diameter of UCP at the bottom of hardened layer can be decreased by about 20%. Compared with conventional quenching, surface hardness was enhanced by about 20% through laser surface quenching, contributing to the wear resistance. However, the hard and brittle surface layer tends to be crack source during the impact process, leading to the deterioration of final impact toughness. Under the identical laser parameters, the impact absorbed energy is similar in both single and double quenching, which is about 25% of that before laser surface quenching. The impact absorbed energy can be increased from 22J to 28J by preheating at 160 C during the laser surface quenching.
关键词： Impact toughness,Grain size,Cementite,Laser surface quenching,Double quenching,Wear
更新于2025-09-19 17:13:59
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Ratiometric fluorometric determination of silver(I) by using blue-emitting silicon- and nitrogen-doped carbon quantum dots and red-emitting N-acetyl-L-cysteine-capped CdTe quantum dots
摘要： A ratiometric fluorometric assay for silver(I) is described. The method makes use of a dually emitting quantum dot hybrid, which is composed of (a) blue-fluorescent silicon- and nitrogen-doped carbon quantum dots (CQDs), and (b) of red-emitting CdTe quantum dots (QDs) capped with N-acetyl-L-cysteine. The red-emitting CdTe QDs undergo strong and specific quenching by Ag(I), whereas the blue-emitting N,Si-CQDs are not quenched. The two kinds of QDs are mixed and used as a ratiometric fluorescent probe. A linear relationship is found between the log of intensities [(I608/I441)0/(I608/I441)] and the concentration of Ag(I) in the range from 5.0–1000 nM, and the limit of detection (at S/N = 3) is 1.7 nM. Possible interferents (including 17 general metal ions, 12 anions and fulvic acid) do not interfere with the determination. The assay was successfully used for the determination of Ag(I) in surface water and wastewater samples. The fluorescence quenching mechanism of the ratiometric assay system was also discussed in detailed.
关键词： Fluorescence quenching mechanism,Surface water,Nitrogen-doped carbon dots,Silver ions,Silicon-doped carbon dots,Wastewaters,3-Aminopropyltriethoxysilane functionalized carbon dots,Quenching efficiency,Dual-emission quantum dots hybrid,Fluorescent probe
更新于2025-09-19 17:13:59
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Development of sulfur doped carbon quantum dots for highly selective and sensitive fluorescent detection of Fe2+ and Fe3+ ions in oral ferrous gluconate samples
摘要： Sulfur-doped carbon quantum dots (S-CQDs) with stable blue fluorescence were synthesized through a facile one-step hydrothermal method by using ascorbic acid and thioglycolic acid as carbon and sulfur sources. The prepared S-CQDs exhibited a sensitive and selective response to Fe3+ ions in comparison with Fe2+ and other metal ions, In the presence of adequate H2O2, Fe2+ was completely transformed to Fe3+ that is the determinable form of iron ions, and the difference in the change of the fluorescence intensity of S-CQDs before and after adding H2O2 was used for detection of Fe2+ ions, respectively. Under the optimum experimental conditions, the fluorescence intensity of S-CQDs gradually decreased with increasing of Fe3+ concentration ranging from 0 to 200 mM. Good linearity was achieved over the range of 0-200 mM. The detection limit of the developed method was 0.050 mM for Fe3+. The recoveries of Fe2+ spiked in real samples ranged from 98.2% to 112.4%. Finally, the proposed S-CQDs integrated with Fenton system was applied to the detection of Fe2+ and Fe3+ ions in oral ferrous gluconate samples, which presents potential applications in the speciation and determination of Fe2+ and Fe3+ ions in complex samples.
关键词： Fluorescence quenching,Iron supplement,Iron,Sulfur co-doped,Carbon quantum dot
更新于2025-09-19 17:13:59
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Study of Interfacial Charge Transfer from an Electron Rich Organic Molecule to CdTe Quantum Dot by using Sterna??Volmer and Stochastic Kinetic Models
摘要： Photoinduced electron transfer from N-methylaniline (NMA) to a photoexcited CdTe quantum dot (QD*) is studied in toluene. The PET mechanism at low to moderate quencher (NMA) concentrations (< 0.08 M) remains mostly collisional with some contributions from QD-NMA complex formation. However, at high quencher concentrations (> 0.10 M), QDs form larger numbers of static complexes with NMA molecules leading to a steep positive deviation in the steady-state Stern–Volmer curves. An isothermal titration calorimetry (ITC) study confirms the formation of QD-NMA complexes (K ~ 150 M?1) at high quencher concentrations. Fitting our experimental data using a stochastic kinetic model indicates that the number of NMA molecules attached per QD at highest NMA concentration (~ 0.16 M) used in this study decreases from ~ 0.76 to ~ 0.47 with reducing the QD size from ~ 5.2 nm to ~ 3.2 nm. However, the PET rate increases with decreasing QD size, which is commensurate with the observation that the chemical driving force (ΔG) increases with decreasing the QD particle size. We have analyzed the PET kinetics mainly by using Stern-Volmer fittings. However, in some cases Tachiya’s stochastic kinetic model is used for stoichiometric analysis, which seems to be useful only at high quencher concentrations. The measured PET rate coefficients in all the cases are found to be at least an order of magnitude lower when compared to the diffusion-controlled rate of the reaction medium.
关键词： quantum dot,time-resolved fluorescence,photoinduced electron transfer,Stern–Volmer analysis,bimolecular quenching
更新于2025-09-19 17:13:59
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Facile and highly effective synthesis of nitrogen-doped graphene quantum dots as a fluorescent sensing probe for Cu2+ detection
摘要： Nitrogen-doped graphene quantum dots (N-GQDs) with high blue fluorescence efficiency were synthesized by the hydrothermal method from p-Phenylenediamine and p-Coumaric acid. The N-GQDs possess several superiorities, most significantly in excellent solubility and superior photostability. Besides, the as-prepared N-GQDs exhibit a uniform size distribution with a diameter of about 3.8±0.5 nm. After dispersing the N-GQDs in water, the formed aqueous solution still presents a stable and homogeneous phase even after 2 months at room temperature. The N-GQD dispersion was further utilized as sensing probes for the selective detection of copper ions (Cu2+), which is realized by the photoluminescence (PL) quenching of N-GQDs after adding Cu2+. The detection limit for Cu2+ was found to be 57 nM L-1, with superior selectivity in the presence of other commonly interfering metal ions. The presented results in this study provide a facile and high-efficiency method for synthesizing N-GQDs, with ultra-high detectivity and selectivity for Cu2+ detection, offering numerous opportunities for the development of biosensing, bioimaging, environment monitoring, and others.
关键词： Nitrogen-doped graphene quantum dots,Hydrothermal method,Photoluminescence quenching,Cu2+ detection
更新于2025-09-19 17:13:59
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Study on the interactions between graphene quantum dots and Hg(II): Unraveling the origin of photoluminescence quenching of graphene quantum dots by Hg(II)
摘要： The present investigation reveals that when Hg(II) interacts with the colloidal solution of graphene quantum dots (GQDs), initially it forms complex with GQDs and then reduces to Hg(0) and Hg(I) resulting the complete quenching of GQDs blue luminescence. This is in contradiction with the earlier reports in which the quenching of GQDs by Hg(II) is attributed to complexation alone. In order to understand the reasons for the quenching of GQDs by Hg(II), a detailed study was undertaken by varying the pH of GQDs solution, incubation time and concentration of Hg(II). The emission studies indicate that formation of Hg(0) is less favorable at pH 7 whereas its formation is more favorable at pH 13. It is assumed that the formation of Hg(OH)2 in alkaline pH facilitates Hg(II) reduction easier than at neutral pH. The SEM and TEM images confirm the presence of spherical Hg(0) particles with different sizes depending upon Hg(II) concentration, pH and incubation time. The results obtained from emission, XPS and differential pulse voltammetry (DPV) studies reveal that Hg(II) was reduced to Hg(0) via Hg(I) on GQDs surface. The differential pulse voltammogram of 40 min incubated Hg(II)-GQDs coated GC electrode shows three oxidation peaks at 0.34, 0.48 and 0.65 V, corresponding to Hg(I) to Hg(II) and Hg(0) to Hg(II), respectively.
关键词： metallic Hg,incubation time,mechanism for quenching,effect of pH,Interaction of GQDs with Hg(II)
更新于2025-09-19 17:13:59
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Ultra-trace level Chemosensing of Uranyl ions; Scuffle between Electron and Energy Transfer from Perovskite Quantum Dots to Adsorbed Uranyl Ions
摘要： This work attempts to address the challenge of trace level detection of uranyl ions using highly fluorescent perovskite quantum dots. The fluorescent probe CsPbBr3 perovskite quantum dots (PQDs) in toluene, synthesized via hot-injection method allows complete fluorescence quenching within seconds detecting ppb level concentration of uranyl ions. The mechanistic pathway is deeply investigated and proposed through zeta potential/DLS measurement, the extent of spectral overlap by the change in length of ligands of PQDs, alignment of acceptor-donor energy levels, the unlikeliness of cation exchange and TRPL studies. This study opens new insights into designing the correct combination of the probe (involving PQDs) and analyte (involving metal ions) for trace level sensing of metal ions.
关键词： Sensing,Quantum Dots,Uranyl Ion,Quenching,Perovskite,Fluorescence
更新于2025-09-19 17:13:59
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An ultra-selective fluorescence method with enhanced sensitivity for the determination of manganese (VII) in food stuffs using carbon quantum dots as nanoprobe
摘要： A novel fluorescence method was for the first time established for the efficient determination of permanganate (Mn(VII)) based on sulfur, chlorine and nitrogen co-doped carbon quantum dots (S,Cl,N-CQDs). The S,Cl,N-CQDs was prepared via a fast and simple acid-base neutralization method. The fluorescence of S,Cl,N-CQDs could be dramatically quenched by Mn(VII) ascribed to a combination of inner filter effect (IFE) and dynamic quenching. Under the optimal working conditions, the S,Cl,N-CQDs-based nanoprobe exhibited high selectivity and sensitivity towards Mn(VII) sensing. A good linear Stern-Volmer equation was obtained for Mn(VII) in a wide concentration range of 0.05–110 μM with a detection limit as low as 12.8 nM. The proposed fluorescence method also exhibits additional advantages of great simplicity, fast in analysis and low cost. The as-fabricated fluorescent nanoprobe was successfully applied for the determination of Mn(VII) monitoring in complex food matrix.
关键词： Cl,fluorescence quenching,Mn(VII),S,food samples,N-CQDs
更新于2025-09-19 17:13:59
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Luminescence of Cr3+/Yb3+ co-doped oxyfluoride silicate glasses for crystalline silicon solar cell down-conversion devices
摘要： Oxy?uoride silicate glasses co-doped with Cr3+ and Yb3+ ions were fabricated in this work. High △T (178–214 °C) value demonstrated that the thermal stability of the prepared glasses were better than tellurite and germanate glasses. X-ray di?raction (XRD) curves proved the amorphous nature of the glasses, the energy dispersive spectroscopy (EDS) analysis and Fourier Transform infrared spectroscopy (FT-IR) curves explored the network structure of glasses. The photoluminescence excitation (PLE) and photoluminescence emission (PL) spectra show that the glasses absorption peaks located at 430 nm (Cr3+:4A2g - 4T1g (P)) and 627 nm (Cr3+:4A2g - 4T2g), while the emission peak close to 1010 nm (Yb3+:2F5/2 -2F7/2), which meets the condition of energy down-conversion. Besides, the energy transfer e?ciency (ηCET = 33.5%) and the quantum cutting e?ciency (ηQE = 133.5%) were calculated from the measured decay curves. These values were higher than Cr3+/Yb3+ co-doped ?uorosilicate glass with incorporating of CaF2 (21.5% and 123.5%) and Tb3+/Yb3+ oxy?uoride glass (13.5% and 113.5%), indicating the prepared samples are conducive to the energy transfer from Cr3+ to Yb3+ ions. The experimental results reveal that the oxy?uoride silicate glasses have potential application prospects in crystalline silicon (c-Si) solar cells.
关键词： Oxy?uoride silicate glasses,Melt-quenching method,Down-conversion and near-infrared luminescence emission,Crystalline silicon (c-Si) solar cells
更新于2025-09-19 17:13:59