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Spectroscopic peculiarities of excitation and emission processes as well as relaxation dynamic of excited states in doubly and triply doped Gd3Ga3Al2O12:Ln3+ (Ln3+=Eu3+, Tb3+, Ce3+) crystals
摘要： Spectroscopic properties of Gd3Ga3Al2O12 (GGAG) single crystals co-doped with various configurations of (Eu + Tb); (Eu + Ce); (Tb + Ce) and (Eu+ Tb + Ce) ions have been investigated. The effect of distinct Ln3+ co-doping variations on luminescence of garnet crystals was studied using the different excitation wavelengths. The Ln3+-Ln3+ and host-Ln3+ interplays have been considered in doubly and triply doped GGAG:Ln3+. The crystals containing cerium ions are characterized by mainly broadband emission in the 450–750 nm spectral region that is adequately modified in green and red spectral range in the samples co-doped with terbium and europium, respectively. The Eu3+ luminescence in materials under study is selectively excited employing solely f-f europium transitions. Contrary to that, emission of terbium and cerium occur as result of interaction with Gd3+ and adjacent co-dopants.
关键词： GGAG garnet crystals,Luminescence,Ln-Ln energy transfer
更新于2025-09-23 15:23:52
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Influence of GaN- and Si?N?-Passivation Layers on the Performance of AlGaN/GaN Diodes With a Gated Edge Termination
摘要： This paper analyses the influence of the GaN and Si3N4 passivation (or 'cap') layer on the top of the AlGaN barrier layer on the performance and reliability of Schottky barrier diodes with a gated edge termination (GET-SBDs). Both GaN cap and Si3N4 cap devices show similar dc characteristics but a higher density of traps at the SiO2/GaN interface or/and an increase of the total dielectric constant in the access region result in higher RON-dispersion in GaN cap devices. The leakage current at medium/low temperatures in both types of devices shows two low-voltage-independent activation energies, suggesting thermionic and field-emission processes to be responsible for the conduction. Furthermore, a voltage-dependent activation energy in the high-temperature range occurs from low voltages in the GaN cap devices and limits their breakdown voltage (VBD). Time-dependent dielectric breakdown measurements show a tighter distribution in Si3N4 cap devices (Weibull slope β = 3.3) compared to GaN cap devices (β = 1.8). Additional measurements in plasma-enhanced atomic layer deposition (PEALD)-Si3N4 capacitors with different cap layers and TCAD simulations show an electric field distribution with a strong peak within the PEALD-Si3N4 dielectric at the GET corner, which could accelerate the formation of a percolation path and provoke the device breakdown in GaN cap SBDs even at low-stress voltages.
关键词： Si3N4 cap,GaN cap,AlGaN/GaN Schottky diode,reliability,breakdown voltage,passivation layer,off-state,Activation energy
更新于2025-09-23 15:23:52
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Tunable white-light emission from Pr3+/Dy3+ co-doped B2O3 - TeO2 PbO - ZnO Li2O - Na2O glasses
摘要： In this paper, structural and optical analysis of boro-tellurite based glasses co-doped with Dy3+ and Pr3+ ions has been carried out. The glasses were fabricated by traditional melt quenching technique. XRD results confirm the amorphous-like nature of the glasses. FTIR spectroscopy was applied to explore the functional groups and interactions for the samples. The transition temperatures of glasses were identified by TGA/DSC analysis. Optical absorption and emission spectra of all the glasses have been recorded in the UVe Vis- NIR spectral range. Tauc's method was applied to determine the direct and indirect optical band gaps. Luminescence spectra show intense emission bands at ～482 nm and ～574 nm wavelengths under λexc = 388 nm corresponding to Dy3+: 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions. Decay time data revealed the occurrence of a non-radiative energy transfer from Dy3+ to Pr3+ ions. Intense emission bands are identified at ～602 nm (orange), ～487 nm (blue) and ～574 nm (yellow) observed upon λexc = 437 nm, corresponding to Pr3+:1D2→3H4, Pr3+:3P0,1,2 → 3H4/Dy3+: 4F9/2 → 6H13/2 and Dy3+: 4F9/2 → 6H13/2 transitions, respectively, where the Dy3+ emissions are due to energy transfer from Pr3+ to Dy3+ ions. The CIE chromaticity results confirm that different colors can be generated by tuning the exciting wavelength, where all the glasses are capable to emit white light under λexc = 388 nm, while at λexc = 437 nm the samples (S2eS4) emit reddish orange light. Accordingly, it is plausible to suggest these glasses for white LED and SSL applications.
关键词： Optical absorption,Photoluminescence,W-LEDs,Raman spectroscopy,Borotellurite glass,Energy transfer
更新于2025-09-23 15:23:52
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Inverse logarithmic derivative method for determining the energy gap and the type of electron transitions as an alternative to the Tauc method
摘要： We present a method derived from Mott and Davies or Cody equation for calculating energy gap based on spectrophotometric measurements. The method has been tested on thin film TiO2 and MoS2/TiO2 bilayer produced by RF magnetron sputtering. The presented examples indicate that the Tauc and McLean methods, which are usually used to analyse data, are not justified in many cases, especially for multilayers. In the Tauc method, the problem is to determine the energy gap without knowing the nature of the optical transition. The McLean method involves fitting the power function which may cause difficulties in the proper selection of the fitting range. The presented method is based on the transformation of measurement data using inverse logarithmic derivative and performing of linear fittings. Our method does not assume value of the parameter m describing the nature of the optical transition and does not require knowledge of the thickness of the layers. The value of energy gap and parameter m can be obtained simultaneously thanks to one linear fit. In addition, this method has a practical advantages over methods of McLean and Tauc, which are described in the article.
关键词： Tauc equation,Cody equation,Optical transitions,Energy gap,Multilayer
更新于2025-09-23 15:23:52
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Adaptive Decentralized Control of Residential Storage in PV-Rich MV-LV Networks
摘要： The rapid adoption of residential-scale photovoltaic (PV) systems in low voltage (LV) networks combined with the falling prices of residential-scale battery energy storage (BES) systems is paving the way for a future in which customers could locally supply most of their energy needs. However, off-the-shelf (OTS) storage systems operate for the sole benefit of the customer (reducing grid imports). This means that charging might not occur during times of high PV generation, resulting in technical issues on LV and medium voltage (MV) networks. This work proposes an adaptive decentralized control strategy for residential-scale BES systems to reduce voltage and thermal issues whilst still benefiting customers. With this strategy, the power charging and discharging rates constantly adapt throughout the day based on clear-sky irradiance, PV generation, demand, and state of charge; significantly reducing reverse power flows and ensuring adequate storage capacity the next morning. A real Australian MV feeder with realistically modelled LV networks is studied using smart meter data. Results demonstrate that the proposed control strategy overcomes the limitations of the OTS BES. It is also shown it can be as effective as an ideal optimization-based approach, being able to manage all technical issues without significantly affecting customers.
关键词： PV Systems,Self-Sufficiency,Distribution Networks,Battery Energy Storage Systems
更新于2025-09-23 15:23:52
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Kalman Filtering Technique for Rooftop-PV System under Abnormal Grid Conditions
摘要： This paper presents a robust extended complex Kalman Filter (RECKF) based control for multifunctional double stage grid-connected solar photovoltaic array (SPVA) system. The main contributions of presented paper, include: 1) real power generation from SPVA fulfils the requirement of the connected loads and it provides the surplus power to the distribution network, 2) it behaves as a distribution static compensator, which performs various functionalities such as grid currents balancing, harmonics mitigation, unity power factor operation, 3) it is capable to operate under polluted grid scenarios such as under voltage, over voltage and imbalanced grid voltages. The SPVA feed-forward term is incorporated in the control technique to enhance the dynamic response of the system. The real coded particle swarm optimization (RCPSO) based metaheuristic approach is used for optimal tuning of the DC link voltage PI (Proportional Integral) controller. Simulation results illustrate the effectiveness of presented control algorithm under variations in point of common coupling (PCC) voltage. Test results illustrate the behaviour of grid-connected SPVA system subjected to various perturbations such as under voltages, over voltages, distorted and imbalanced grid voltages etc. The THDs (Total Harmonic Distortions) of grid currents are achieved well within recommended limits.
关键词： Power quality,Renewable energy,Solar photovoltaic array,Harmonics,VSC,Optimization
更新于2025-09-23 15:23:52
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Image Enhancement Using Patch-Based Principal Energy Analysis
摘要： The visual quality of a captured image is often degraded by complicated lighting conditions in various real-world environments. This quality deterioration probably leads to the significant performance drop in many algorithms of computer vision, which require high-visibility inputs for precise results. In this paper, a novel method for image enhancement is proposed with the principal energy analysis. Specifically, based on the key observation that the illumination component is dominant over a small local region, the corresponding energy is efficiently separated from the scene reflectance by exploiting the subspace analysis. Owing to this clear separation, the illumination component can be easily adjusted independent of the reflectance layer for better visual aesthetics. In contrast to previous methods that still suffer from the exaggerated or conservative restoration yielding the loss of details and defects of halo artifacts, the proposed scheme has a good ability to enhance the image contrast while successfully preserving the color attribute of the original scene. Moreover, the proposed method is conceptually simple and easy to implement. Experimental results demonstrate the effectiveness of the proposed method even under diverse lighting conditions, e.g., low light, casting shadow, uneven illuminations, and so on, and the superiority of the proposed method over previous approaches introduced in the literature.
关键词： Quality deterioration,principal energy analysis,subspace analysis,illumination component,image enhancement
更新于2025-09-23 15:23:52
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[IEEE 2018 OCEANS - MTS/IEEE Kobe Techno-Ocean (OTO) - Kobe, Japan (2018.5.28-2018.5.31)] 2018 OCEANS - MTS/IEEE Kobe Techno-Oceans (OTO) - A High Dynamic Range in Situ Flow Sensor
摘要： High dynamic range and high accuracy flow sensor is a highly desirable device in quantifying mixing in the atmosphere and the ocean, which is critical in our understanding of energy dissipation and flux studies. We discuss a design that utilizes only a single point sensor in different angles, based on our novel oriented temperature Fabry-Perot using interferometry approach. We report the sensitivity of a high-dynamic range sensor head orientation in such configuration. We discuss initial configuration, data collection, processing, analysis and calibration including sensor orientation for future deployment.
关键词： Fabry-Perot interferometer,flow meter,turbulence,kinetic energy dissipation,fiber optics
更新于2025-09-23 15:23:52
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[IEEE 2018 10th IAPR Workshop on Pattern Recognition in Remote Sensing (PRRS) - Beijing (2018.8.19-2018.8.20)] 2018 10th IAPR Workshop on Pattern Recognition in Remote Sensing (PRRS) - FPGA Optimization for Hyperspectral Target Detection with Collaborative Representation
摘要： Most applications based on wireless sensor networks (WSN) have devices with constraints of limited energy and computational/storage capabilities. The traditional security mechanisms are not desirable to these applications. A lightweight security and energy-efficient clustering protocol was proposed in this paper to solve the security problem in the clustering-based sensor networks. Firstly, a lightweight security algorithm is proposed to meet the security requirements, which reduces the communication overload by using the transmission key index. Secondly, in the process of clustering, the base station (BS) and cluster head (CH) use lightweight authentication procedure to verify the identities hierarchically, to reduce the risk of attacks from malicious nodes posing as BS or CH. Thirdly, the proposed protocol is analyzed in the aspects of security and energy consumption. Simulation results show that the proposed protocol not only enhances the network security but also improves the energy efficiency.
关键词： Lightweight security,Energy-efficient protocol,Clustering WSN
更新于2025-09-23 15:23:52
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Multifunctional BaTiO <sub/>3</sub> -(Bi <sub/>0.5</sub> Na <sub/>0.5</sub> )TiO <sub/>3</sub> -based MLCC with high energy storage properties and temperature stability
摘要： BaTiO3-(Bi0.5Na0.5)TiO3 (BTBNT)-based multilayer ceramic capacitor (MLCC) chips with the inner electrodes being Ag0.6/Pd0.4 are prepared by a roll-to-roll casting method. The BTBNT-based MLCC chips with ten-dielectric layers can be sintered very well at a low temperature of 1130°C via two step sintering (TSS). X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that MLCC chips are a core-shell structure with two phases coexistence. The core exhibits a tetragonal phase at room temperature and then gradually changes into a cubic phase when the temperature increases above Tc (175°C). While, the shell exhibits a pseudocubic phase at all tested temperature from 25°C to 500°C. BTBNT-based MLCC chips exhibit a broad temperature stability and meet the requirement of Electronic Industries Association (EIA) X9R specifications. In terms of energy storage performance, a large discharge energy density of 3.33 J/cm3 can be obtained at 175°C under the applied electric field of 480 kV/cm. Among all tested temperature ranging from -50°C to 200°C, the energy efficiency of all chips is higher than 80%, even under a high applied electric field. The experimental results indicate that this novel BTBNT-based X9R MLCCs can be one of the most promising candidates for energy storage applications, especially operated in high temperature.
关键词： Energy storage,X9R,Two-step sintering (TSS),Core-shell structure,Multilayer ceramic capacitor (MLCC)
更新于2025-09-23 15:23:52