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Reversible/Irreversible Photobleaching of Fluorescent Surface Defects of SiC Quantum Dots: Mechanism and Sensing of Solar UV Irradiation
摘要： Knowledge about photobleaching properties of the fluorescent surface defects of the semiconductor quantum dots (QDs) is crucial for their applications. Here, the photobleaching properties of the fluorescent surface defects of the colloidal 3C-SiC QDs are reported. The combined experimental and theoretical study reveals that the observed violet fluorescence at around 392 nm stems from the carboxylic acid group-related surface defects. When the SiC QDs are exposed to the UV irradiation, the 392 nm fluorescent surface defects show both reversible and irreversible photobleaching, whereas the 438 nm fluorescent surface defects show only irreversible photobleaching. The photochemical mechanisms dominating these phenomena are explored. The photobleaching property of the SiC QDs is utilized to detect the solar UV irradiation with high accuracy. The photobleaching of the SiC QDs is highly sensitive to the hydrogen or metal ion concentration in the colloid solution. These findings deepen the understanding of the properties of the fluorescent surface defects of the SiC QDs and pave the way for their applications in sensing.
关键词： photobleaching,silicon carbide quantum dots,surface defects,fluorescence mechanism
更新于2025-11-19 16:46:39
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The Self-Assembly of Cu-In-S Quantum Dots with Aggregation-Induced Emission into 3D Network Triggered by Cation and Its Application as A Novel Metal-Enhanced Fluorescent Nanosensor for Detecting Zn (Ⅱ)
摘要： A novel self-assembly phenomenon triggered by Zn2+ of Cu-In-S quantum dots with aggregation-induced emission effect was presented in this paper. Hydrophilic Cu-In-S quantum dots with aggregation-induced emission effect were successfully prepared. They were monodisperse spherical nanoparticles with the diameter of 2.8 ± 0.4 nm and had weak fluorescence in aqueous solution. However, the solution emitted strong fluorescence after addition of Zn2+. The results of TEM and SEM indicated the monodisperse quantum dots self-assembled into 3D networks of Cu-In-S quantum dots-Zn2+, which hindered the motion of quantum dots. Besides, the Zn2+ in the mixture passivated the surface defects. The phenomenon also proved by florescence lifetime and XPS. Thus the radiation decay decreased and followed by strong fluorescent emission. Interestingly, the degree of aggregation was proportional to the amount of Zn2+ and the fluorescent intensity. Based on this interesting phenomenon, a novel metal enhanced fluorescent nanosensor for detecting Zn2+ was established. The results demonstrated the proposed method had a good selectivity and linearity in the concentration range of 0-800 nmol?L-1 with a limit of detection of 1.99 ppb. These results showed a promising future in the field of metal-enhanced fluorescent probes of the Cu-In-S quantum dots.
关键词： Surface defects,Metal-enhanced sensor,Quantum dots,Restriction of motion,Aggregation-induced emission
更新于2025-11-14 15:23:50
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Potential of Near-infrared Spectroscopy to Detect Defects on the Surface of Solid Wood Boards
摘要： Defects on the surface of solid wood boards directly affect their mechanical properties and product grades. This study investigated the use of near-infrared spectroscopy (NIRS) to detect and classify defects on the surface of solid wood boards. Pinus koraiensis was selected as the raw material. The experiments focused on the ability to use the model to sort defects on the surface of wood into four types, namely live knots, dead knots, cracks, and defect-free. The test data consisted of 360 NIR absorption spectra of the defect samples using a portable NIR spectrometer, with the wavelength range of 900 to 1900 nm. Three pre-processing methods were used to compare the effects of noise elimination in the original absorption spectra. The NIR discrimination models were developed based on partial least squares and discriminant analysis (PLS-DA), least squares support vector machine (LS-SVM), and back-propagation neural network (BPNN) from 900 to approximately 1900 nm. The results demonstrated that the BPNN model exhibited the highest classification accuracy of 97.92% for the model calibration and 97.50% for the prediction set. These results suggest that there is potential for the NIR method to detect defects and differentiate between types of defects on the surface of solid wood boards.
关键词： Surface defects,BPNN,PLS - DA,LS-SVM,Near-infrared spectroscopy,Solid wood boards
更新于2025-09-23 15:22:29
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Investigation of local geometrical structure, electronic state and magnetic properties of PLD grown Ni doped SnO2 thin films
摘要： We have investigated the ferromagnetic behavior, electronic states and local geometrical structure of Ni (2 and 10 at %) doped SnO2 thin films. The films were successfully fabricated with the help of pulsed laser deposition (PLD) technique on Si (100) substrate under ultrahigh vacuum (UHV) condition. X-ray diffraction (XRD) results revealed the single phase character of SnO2 rutile lattice structure with P42/mnm space group. The inclusion of Ni ions into SnO2 matrix induced oxygen vacancy (Vo), enhanced the distortion in octahedral local symmetry and reduced the oxidation state of the host Sn4+ (SnO2) to Sn3+ (Sn2O3) these details have been estimated by Raman scattering, Near edge X-ray absorption fine structure (NEXAFS) spectra at Ni L3,2 and O K edges. Further quantitative details on the local geometrical structure around Ni ions were obtained via fitting the experimental Fourier transforms EXAFS spectra |X(R)| with FEFF6 code. The magnetization measurements performed at room temperature (RT) infers that the observed magnetic behavior of the films seems to be relevant to the same crystal growth condition (UHV) and might not be limited directly to the Ni dopant concentrations. The FM signal and the role of surface defects have been discussed based spin-split impurity band difference in the saturation moments even with increase the Ni content. Hence, the similarity in Ni doped SnO2 films displayed ferromagnetic (FM) signal, and there was no significant Ferromagnetism etc. percolation mechanism.
关键词： surface defects,XANES spectra,SnO2 nanostructured thin film,PLD,local symmetry,XRD,NEXAFS
更新于2025-09-23 15:22:29
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Increasing the laser-acoustic method efficiency for testing metal products by using 3D visualization
摘要： The article proposes a solution to the problem of increasing the efficiency of the laser-acoustic method of non-destructive testing. An approach to increasing the probability of detecting surface defects of microscopic dimensions in metals is considered. Due to the increased accuracy of determining defect parameters, the detail of 3D visualization of testing results was improved.
关键词： non-destructive testing,3D visualization,surface defects,metals,laser-acoustic method
更新于2025-09-23 15:21:01
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Structured-illumination Makyoh-topography: optimum grid position and its constraints
摘要： Complementing conventional Makyoh topography with structured illumination using a sparse square grid, the large-scale surface shape can be calculated with a deflectometry approach, while the sample’s morphology can still be imaged. However, the grid’s image must be sharp not to mask the Makyoh image of the sample morphology. In this paper, the instrumental conditions for the grid sharpness are established. The two main types of Makyoh set-ups (lens and mirror based) are analysed. It is shown that the lens-based set-ups allow the position of the grid to be sharp on the Makyoh image. However, for mirror-based set-ups this is not possible because of geometrical instrumental constraints. The calculations are corroborated with experiments.
关键词： Makyoh topography,surface defects,structured illumination,deflectometry,geometrical optics,flatness testing
更新于2025-09-23 15:21:01
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Induced Photonic Response of ZnO Nanorods Grown on Oxygen Plasma-Treated Seed Crystallites
摘要： We examined the influence of O2 plasma treatment for the ZnO seed layer (SL) crystallites on the material characteristics of ZnO nanorods (NRs) synthesized by the hydrothermal method. Diode photocurrent and photo-response transient characteristics of the p-Si/n-ZnO-NR heterojunction-based ultraviolet (UV) photodetectors were also examined according to the plasma treatment for the SLs. The superior optical properties of NRs were measured from the photoluminescence by exhibiting 4.6 times greater near-band edge emission when grown on the O2-plasma-treated SL. The degree of (002) orientation of the NR crystals was improved from 0.67 to 0.95, as revealed by X-ray diffraction analysis, and a higher NR surface density of ~80 rods/μm2 with a smaller mean diameter of 65 nm were also observed by the SL modification using plasma-treatment. It was shown by X-ray photo-electron spectroscopy that this improvement of NR crystalline quality was due to the recovery of stoichiometric oxygen with significant reduction of oxygenated impurities in the SL crystals and the subsequent low-energy growth mode for the NRs. UV PDs fabricated by the proposed SL plasma treatment technique showed significantly enhanced UV-to-dark current ratio from 2.0 to 83.7 at a forward bias of +5 V and faster photo-response characteristics showing the reduction in recovery time from 16 s to 9 s.
关键词： photoluminescence,surface defects,oxygen plasma,ZnO seed crystals,hydrothermal
更新于2025-09-23 15:21:01
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Method of Laser Thermal Image Spectroscopy for Surface Diagnostics
摘要： A new method of laser-thermal imaging spectroscopy is presented and the results of studying samples with different absorption coefficients are reported. The times required for heating the surface of these samples by laser radiation with a wavelength of 0.634 μm to a temperature exceeding the initial value by 0.3°C are calculated and compared with the experimental data. The depths of laser-radiation penetration into the surface layer of the material under the condition of external and internal reflection are calculated. The depth determines the transition region in which the energy of absorbed laser radiation transforms into the thermal energy of the substance. It is shown that the method allows the surface of materials to be studied and zones with different optical and physical-chemical properties to be studied. The method can be used to solve problems in the field of medicine, surface restoration, forensic examination and others.
关键词： defect substance,surface defects,surface heating time,spectral absorption coefficient,penetration depth of laser radiation
更新于2025-09-19 17:13:59
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Dynamic behavior modeling of laser-induced damage initiated by surface defects on KDP crystals under nanosecond laser irradiation
摘要： the issue of laser-induced damage of transparent dielectric optics has severely limited the development of high-power laser systems. exploring the transient dynamic behaviors of laser damage on KDp surface by developing multi-physics coupling dynamics model is an important way to reveal the mechanism of nanosecond laser damage. In this work, KDP crystals are taken as an example to explore the mechanism of laser-induced surface damage. Based on the theories of electromagnetic field, heat conduction and fluid dynamics, a multi-physics coupling dynamics model is established for describing the evolution of nanosecond damage processes. The dynamics of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation are simulated with this model. it is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of temperature field and crater morphology during subsequent laser irradiation is helpful to understand the laser damage process. The feasibility of this model is verified by the morphology information of typical defect-induced laser damage. this work provides further insights in explaining the laser-induced damage by surface defects on KDp crystals. the model can be also applied to investigate the laser damage mechanisms of other transparent dielectric optics.
关键词： laser-induced damage,multi-physics coupling model,nanosecond laser irradiation,KDP crystals,surface defects
更新于2025-09-19 17:13:59
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Ligand-Assisted Reconstruction of Colloidal Quantum Dots Decreases Trap State Density
摘要： Increasing the power conversion efficiency (PCE) of colloidal quantum dot (CQD) solar cells has relied on improving the passivation of CQD surfaces, enhancing CQD coupling and charge transport, and advancing device architecture. The presence of hydroxyl groups on the nanoparticle surface, as well as dimers—fusion between CQDs—has been found to be the major source of trap states, detrimental to optoelectronic properties and device performance. Here, we introduce a CQD reconstruction step that decreases surface hydroxyl groups and dimers simultaneously. We explored the dynamic interaction of charge carriers between band-edge states and trap states in CQDs using time-resolved spectroscopy, showing that trap to ground-state recombination occurs mainly from surface defects in coupled CQD solids passivated using simple metal halides. Using CQD reconstruction, we demonstrate a 60% reduction in trap density and a 25% improvement in charge diffusion length. These translate into a PCE of 12.5% compared to 10.9% for control CQDs.
关键词： trap states,dimers,surface defects,photovoltaics,Quantum dots
更新于2025-09-19 17:13:59