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Polycrystal Synthesis, Crystal Growth, Structure, and Optical Properties of AgGaGe <sub/><i> <i>n</i> </i> </sub> S <sub/> 2( <i> <i>n</i> </i> +1) </sub> ( <i>n</i> = 2, 3, 4, and 5) Single Crystals for Mid-IR Laser Applications
摘要： AgGaGenS2(n+1) crystal is a series of quaternary for mid-IR laser applications of nonlinear optical materials converting a 1.064 μm pump signal (Nd:YAG laser) to 4?11 μm laser output, but only AgGaGeS4 has attracted the most attention, remaining the other promising AgGaGenS2(n+1) crystal whose physicochemical properties can be modulated by n value. In this work, AgGaGenS2(n+1) (n = 2, 3, 4, and 5) polycrystals are synthesized by vapor transport and mechanical oscillation method with di?erent cooling processes. High-resolution X-ray di?raction analysis and re?nement have revealed that all the four compounds are crystallized in the noncentrosymmetric orthorhombic space group Fdd2, resulting in the excellent nonlinear optical property, and the distortion of tetrahedron with the variation of n value causes the discrepancy of physicochemical property. Besides, using the modi?ed Bridgman method, AgGaGenS2(n+1) single crystals with 15 mm diameter and 20?40 mm length have been grown. We have discussed the structure and composition of AgGaGenS2(n+1) by XPS spectra and analyzed the three kinds of vibration modes of tetrahedral clusters by the Raman spectra. The Hall measurement indicates that the AgGaGenS2(n+1) single crystals are p-type semiconductor, and the carrier concentration decreases with the increasing n value. All the transmittances of as-grown AgGaGenS2(n+1) samples exceeds 60% in the transparent range, especially the transmittance of AgGaGe2S6, is up to 70% at 1064 nm, and the band gap of as-grown crystal increases from 2.85 eV for AgGaGe2S6 to 2.92 eV for AgGaGe5S12. After a thermal annealing treatment, the absorptions at 2.9, 4, and 10 μm have been eliminated, and the band gap changed into the range of 2.89?2.96 eV.
关键词： Hall measurement,nonlinear optical materials,thermal annealing treatment,vapor transport,AgGaGenS2(n+1),Bridgman method,Raman spectra,mid-IR laser applications,XPS spectra,mechanical oscillation method
更新于2025-11-14 15:27:09
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Graphene oxide/ZnO nanorods/graphene oxide sandwich structure: The origins and mechanisms of photoluminescence
摘要： In this paper, we present the structural and optical properties of Graphene oxide/ZnO nanorods/graphene oxide (GO/ZnO nanorods/GO) nanocomposites prepared via a hydrothermal method on Si (100) substrate. The X-ray diffraction measurements (XRD) confirm that the prepared samples are of hexagonal wurtzite structure with crystallite size around 50-60 nm. It was obvious from scanning electron microscopy (SEM) that by incorporating the ZnO nanorods between the inter-layer of GO confirmed the formation of sandwich-like nanocomposites structure. ZnO nanorods interaction with GO is displayed by the different vibrational frequencies in fourier transform infrared spectroscopy (FTIR). The UV-Vis spectrum reveals the strongest absorption was observed around 370 nm, while calculating optical band gap energy (Eg) of GO/ZnO NRs/GO was found to be 3.15 eV. The photoluminescence (PL) measurements indicates that the ZnO nanorods have a strong visible emission centered at 559 nm attributed to the presence of impurities in the form of oxygen vacancies. After the nanorods were covered with GO layers, the PL intensity of the nanocomposite is quenched and shifted due to charge-transfer process. Consequently, the obtained results may lead to better performance for the optoelectronic applications.
关键词： ZnO nanorods,hydrothermal method,excitation effect,graphene oxide
更新于2025-11-14 15:25:21
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Theoretical and experimental study of PTDPV optical and vibrational properties and its application in white electroluminescent blends
摘要： The polymer Poly[tris(2,5-bis(hexyloxy)-1,4-phenylenevinylene)-alt-(1,3-phenylenevinylene)] (PTDPV) has a broad range of visible emission extending from green to red, and thus may be useful for obtaining a white light emitting blend. Nevertheless, the amount of works found in the literature dealing with the optical emission properties of PTDPV is very small. In this work, we performed a study of the optical properties of this material using photoluminescence and of the vibrational properties using Raman and Fourier Transform Infrared Spectroscopy (FT-IR) techniques. At the same time, we use the Density Functional Theory (DFT) method to calculate the optical, vibrational and molecular properties of PTDPV. We have obtained the best DFT results using a hybrid functional and a simple basis set (DFT / B3LYP and 6–31 g *), without addition of correction or polarization factors (+). To reach these conclusions, we compared the HOMO and LUMO values obtained via DFT with those found in the literature. Furthermore, the Raman and IR simulations obtained using this basis set were compared with the experimental results of the PTDPV, showing great agreement. From the vibrational modes obtained, it was possible, using the Lin model [1–3], based on the Franck Condon approximations, to reconstruct the photoluminescence spectrum of the PTDPV. Based on these reconstructed spectra, it was possible to establish the contribution of the different vibrational modes to the vibronic emissions of the photoluminescence spectrum. The quality of the reconstruction obtained with the DFT results and that obtained with the experimental ones are very close, showing the possibility of using in this reconstruction the calculated vibrational modes when the experimental ones are not available. To demonstrate the application of this material, PFO:PTDPV blends were prepared, with which white photoluminescence was obtained. OLEDs prepared with these blends, in suitable proportions, emitted white light using low excitation power, demonstrating the feasibility of using PTDPV in OLEDs for lighting, which could be prepared by solution on large areas.
关键词： Photoluminescence,Raman and FT-IR,DFT method,PTDPV polymer,White electroluminescence
更新于2025-11-14 15:19:41
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Full color carbon dots through surface engineering for constructing white light-emitting diodes
摘要： White light-emitting diodes (WLEDs) devices are replacing the filament lamp and they can provide a light close to the natural sunlight, which have thus drawn considerable attention in these recent years. It remains a scientific challenge to develop WLEDs using environmentally friendly, easy-to-process and cost-effective phosphors. Here we synthesized blue-, green- and red-carbon dots (denoted as B-, G- and R-CDs) by a facile solvothermal method with high dispersity both in aqueous and organic solvent. The quantum yield (QY) of the R-CDs achieved up to 24.7%. These CDs can be easily dissolved in polyvinylpyrrolidone (PVP) colloid, leading to the production of ultraviolet (UV)-excited LED devices to avoid the retinal damage caused by blue ray excitation. The fluorescence emission of the WLED has a wide band, covering the whole visible light region. Importantly, the influence of doping that gives rise to the change of emissive colors has been elucidated by X-ray photoelectron spectroscopy (XPS) combined with a computation method in order to provide a systematic controllable tuning on the functionalization of CDs. As such, WLEDs were demonstrated with color coordinates of (0.33, 0.33), a color temperature of 5612 K in the CIE chromaticity diagram with good anti-photobleaching and a color rendering index (CRI) of 89.
关键词： polyvinylpyrrolidone,White light-emitting diodes,solvothermal method,UV-excited LED devices,density functional theory,quantum yield,X-ray photoelectron spectroscopy,carbon dots
更新于2025-11-14 15:18:02
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In Situ Generation of AgI Quantum Dots by the Confinement of A?Supramolecular Polymer Network: A Novel Approach for Ultrasensitive Response
摘要： Currently, it is difficult to realize environmentally friendly synthesis of zeolites due to the use of the solvent. Therefore, it is of great importance to realize zeolite synthesis from iron ore tailings (IOTs) by a solvent-free method. In this work, in situ formed zeolite crystals are self-assembled and IOTs are converted into hierarchically porous ZSM-5. After that, the products prepared are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption. The results demonstrate that the samples show well-defined crystallinity and have micro-/mesoporous structures. The BET surface area is estimated to be 319.809 m2 g?1 and the external surface area is 92.693 m2 g?1, which indicate the as-synthesized ZSM-5 is a good hierarchically porous material. This work provides a reference for green synthesis of hierarchically porous ZSM-5 from IOT.
关键词： Hierarchical structure,Iron ore tailings,Solvent-free method,ZSM-5
更新于2025-11-14 15:15:56
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Plastic anisotropy of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy
摘要： Tensile tests of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy specimens in different orientations were conducted, which indicates significant plastic anisotropy of this material. Digital image correlation method added in-situ-tensile tests were carried out to investigate mechanical properties with respect to specified material structures. The results indicate that the plasticity properties of the thick columnar grain and that of other grains are significant different. Under the same stress level, the thick columnar grain yield firstly and bear the main plastic deformation of the whole specimen. The elasto-plastic Poisson's ratio of the thick columnar grains and that of other grains are also different. Tests on layer bands indicate that the coarser microstructures of the layer bands lead a stronger resistance to tensile plastic deformation, but a weaker resistance to shear plastic deformation. In addition, the direction of primary α laths on both sides of the layer bands may be different, and this has an obviously effect on the tensile plastic deformation of the specimen.
关键词： Digital image correlation method,Plastic anisotropy,Laser melting deposited,Titanium alloy,Mechanical properties
更新于2025-10-24 16:40:20
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Full wave analysis of plane wave diffraction by a finite sinusoidal grating: E-polarization case
摘要： Plane wave diffraction studies of a finite sinusoidal grating have previously assumed that the grating length is large in wavelengths and the depth of its corrugations is small compared to a wavelength. This paper introduces a rigorous technique, the Method of Analytical Regularization (MAR), which removes these restrictions. The solution obtained by this method is free from limitations on the parameters of sinusoidal grating and possesses the capability to achieve predetermined accuracy of computations uniformly in a wide frequency band. The results of previous studies, which employed the Wiener-Hopf technique combined with a perturbation method, are compared with those obtained by the MAR; excellent concordance of results in the common parameter regimes of applicability of both methods is found. The different regimes of applicability of each approach are identified; within these, the MAR provides effective and efficient solutions to benchmark problems for testing other approximate techniques.
关键词： efficient computational algorithm in wide frequency band,scattering of E-polarized plane wave,method of analytical regularization,Floquet modes for finite grating,finite sinusoidal grating,Wiener-Hopf technique combined with perturbation method
更新于2025-09-23 15:23:52
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A comprehensive study on the interface states in the ECR-PECVD SiO2/p-Si MOS structures analyzed by different method
摘要： The electrical properties of SiO2/p-Si films deposited by ECR-PECVD were studied at different frequencies (100-1 MHz) and gate voltages (-6–3 V). Results showed a frequency dispersion of C-Vg and G/ω-Vg. With increasing frequency, the capacitance and conductance are strongly decreased. An apparent peak in the depletion regime of the G/ω-Vg plots can be attributed to the existence of density Nss at Si/SiO2. The (Nss)value vary from 1.5 × 10^12 to 0.5 × 10^11 eV^-1 cm^-2, it has been determined by High-Low frequency capacitance technic. The Nss- Vg curve presents a peak at about -3 V, suggesting the presence Nss between the (Si)/SiO2 interface. Hill and Coleman method shows that the Nss decreases with increasing frequency which explains the high value of capacitance at low frequency. The Nss and their relaxation time τ by the conductance method ranged from 1.8 × 10^13 to 1.37 × 10^11 eV^-1 cm^-2 and 5.17 × 10^-7 to 8 × 10^-6 s, in the range (0.189-Ev) and (0.57- Ev) eV, respectively. The Nss was responsible for the non-ideal behavior of C-Vg and G-Vg leading to the breakdown of such device. Comparing the three method results show that parallel conductance is very precise and accurate.
关键词： Capacitance method,Relaxation time,Frequency,Interface states,Metal/Oxide/Semiconductor (MOS),Conductance method
更新于2025-09-23 15:23:52
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Mixed Total Field/Scattered Field-Based Discontinuous Galerkin Frequency-Domain Method for Subsurface Sensing
摘要： To model the responses of electromagnetic surveys for geophysical subsurface sensing, a mixed total field/scattered field-based discontinuous Galerkin frequency-domain (TF/SF DGFD) method is proposed in this paper. The proposed TF/SF DGFD method is implemented at a subdomain level based on the domain decomposition technique. Different subdomains can employ either the TF DGFD framework or the SF DGFD framework, which are then coupled through the Riemann transmission condition. To balance the computation efficiency and accuracy for practical applications, the proposed method prefers to using the SF DGFD framework for subdomains with sources and using the TF DGFD framework for the remaining subdomains. At the interfaces between total field and scattered field subdomains, the Riemann transmission condition is slightly modified by incorporating the background fields due to the physically imposed sources in the background media. In this way, the proposed method only requires surface integrals of the background fields as extra overhead instead of elementwise integration of the scattering objects for the purely scattered field-based method, which can improve the computational efficiency. Also, it is more accurate than the purely TF DGFD method given the same mesh. Numerical examples are studied to examine the performance of the proposed method, which is proven to have better accuracy than the TF DGFD method. The TF/SF DGFD method will facilitate modeling of electromagnetic surveys under complicated geophysical environments for subsurface sensing.
关键词： scattered field,Anisotropy,domain decomposition,discontinuous Galerkin frequency-domain (DGFD) method,total field,subsurface sensing
更新于2025-09-23 15:23:52
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Calculation method of a random beard fibrogram based on the derived Kubelka–Munk theory
摘要： The random beard image method is a newly developed fiber length measurement method with the advantages of speed, reliability and low cost. This paper proposed the methods of acquiring an accurate and stable fibrogram from the transmission image with the random beard image method based on the derived Kubelka–Munk theory. In the dual-beard preparation process, the optical properties of the short fiber region in the beard were changed by the napping effect. To solve this problem, an imitating experiment with five types of wool fibers was designed to obtain the optical coefficient of the maximum value of the fibrograms of 1.03. To eliminate the random error of the sample, the symmetry principle was adopted to determine the start line of the dual-fibrogram, and the weighted smoothing average fibrogram from two dual-beards is used as the final fibrogram. In addition, upon testing 20 types of wool fiber samples by the random beard image method and the international standard instrument Almeter100, the waviness coefficient of 1.10 was determined. A Z-test and Bland–Altman plot were also applied to verify the accuracy and repeatability of the random beard image method. The results show that under the significance level a ? 0.05, the accuracy and the repeatability of the two methods are at the same level. This method sets the foundation for measuring the fiber length distribution parameters, especially the short fiber content.
关键词： fibrogram,dual-beard,Almeter,random beard image method,wool fiber length
更新于2025-09-23 15:23:52