High Current Levels Research Articles

Polyimide-Based Composite Separators for Super-Stable Li Metal-Based Batteries

Metallic lithium (Li) has garnered significant interest from battery industries and academia investigating next-generation anodes, due to its excellent properties: high specific capacity (3860 mAh g-1), the most negative potential (close to -3.04 V vs. SHE), and low density. Unfortunately, inherent challenges associated with inhomogeneous Li plating/stripping and poor Coulombic efficiency impede the pragmatic use of Li metal anode for conventional batteries. Moreover, thermal shrinkage of polyolefin separators presents a critical issue when Li metal batteries are subjected to high current levels, leading to an inability of the separators to shield the cell from short-circuits effectively.The fabrication of polyimide-based composite separators via non-solvent-nduced phase separation (NIPS) is particularly promising for enhancing the electrochemical stability of Li metal batteries. A diversity of functional materials has been examined for the preparation of these composite separators, which have subsequently been assessed in Li metal battery systems. Beyond the development of composite structures, the surface modification of polyimide separators has also been explored to further optimize performance in Li metal batteries. Throughout this talk, we are going to give a talk about our research findings and strategic direction in detail. This presentation would assist many researchers in gaining insights into the design of new battery separators.

Current regulates electron donors for heterotrophic and autotrophic microorganisms to enhance sulfate reduction in three-dimensional electrode biofilm reactors

The variability in industrial production often generates wastewater with an unstable carbon-to-sulfur ratio, challenging the concurrent removal of sulfate and organic compounds. Three-dimensional biofilm electrode reactor (3D-BER) technology offers a promising solution, compatible with both autotrophic and heterotrophic sulfate reduction. In this study, four up-flow 3D-BERs with gradient current levels were operated for nearly 400 days to treat simulated high-concentration sulfate wastewater. The effects of current intensity, hydraulic retention time (HRT), and influent carbon-to-sulfur ratio on sulfate and organic removal were investigated. The composition and functions of microbial communities were analyzed by metagenomic sequencing. The synergistic mechanism between heterotrophic and autotrophic sulfate reduction was examined by delineating their individual contributions to sulfate removal. Under optimized conditions (HRT 60 h, influent carbon-to-sulfur ratio of 1.7, and current intensity of 50 mA), the highest removal efficiencies for SO42- and COD reached 70.47 % and 85.58 %, respectively. Elevated current intensity increased the abundances of Desulfuromonadaceae, Desulfovibrionaceae and Methanobacteriaceae, while decreasing Anaerolineaceae and Geobacteraceae. Key genes involved in carbon fixation and hydrogen-relied sulfate reduction showed lower abundances at high current levels, whereas genes for direct electron uptake from the electrode were more abundant. Batch experiments demonstrated a synergistic effect between autotrophic and heterotrophic sulfate reduction, most pronounced at 50 mA. Our work successfully regulates electron donors for microbial reduction of high-concentration sulfate in 3D-BERs by manipulating current intensity, providing new insights into the application of bioelectrochemical technology for complex industrial wastewater treatment.

Effect of yttrium doping on the properties of Nickel-Iron multiphase heterostructures at high current conditions

Transition metal selenides hold great promise for producing clean hydrogen energy from water electrolysis, but it is not clear how transition metal elements can improve the stability of catalyst performance at high current levels. This work presents the use of nickel foam (NF) as a hydrothermal selenium substrate for yttria-doped multiphase bifunctional catalysts (Y-MSex/NF; M = Ni, Fe). Under high current circumstances, the linked structure of nanosheets and nanoscale microspheres created by hydrothermal selenium enhanced the catalytic reaction area and demonstrated exceptional performance. The overpotentials of the catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were 350 mV and 340 mV, respectively, at a current density of 1000 mA cm−2(j1000). Moreover, stable operation in 1.0 M potassium hydroxide at a current density of 100 mA cm−2for 50 h further demonstrated the good electrocatalytic stability. Demonstrate the potential of selenides doped with the rare earth element yttrium for total water decomposition applications.

INFLUENCE OF WIRE FEED RATE OF HIGH-SPEED ELECTRIC ARC METALLISATION ON STRUCTURE AND CORROSION PROPERTIES OF 30HGSA STEEL COATINGS

The study examines the porosity characteristics, corrosion analysis, and microstructure of iron-based coatings sprayed by supersonic arc metallisation in order to understand the regularity of the influence of the parameters by wire feed rate dependence. The performance of iron-based coatings depends on the integrity of the coating structure. Optimisation of arc spraying parameters allows minimising defects (pores, grain boundaries, unmelted particles, oxides and microcracks) that deteriorate coating properties. At high current levels, the microstructure of the coatings becomes more dense and the particle size decreases, also the average pore size decreases. As the wire feed rate increases, the value of current increases, which leads to the release of more heat energy at the arc to melt the wire and consequently favours the formation of dense coatings with low porosity.

Investigation of degradation dynamics of 265 nm LEDs assisted by EL measurements and numerical simulations

We studied four AlGaN-based 265 nm LEDs with increasing QW thickness (1.4, 3, 6 and 9 nm) during a constant current stress at 100 A cm−2. We focused our attention on the parasitic components of the emission spectra at low current levels and on the optical power recovery observed at high current levels. We associated every parasitic peak or band to a region in the device where they can be generated, also demonstrating if they are related to band-to-band emission or radiative emission through defects. At high current levels, we showed the simultaneous effect of the decrease in injection efficiency in the active region and the increase in non-radiative recombination, by fitting the EQE curves with a mathematical model. Moreover, we associated the optical power recovery with a generation of negative charge near the active region, which led to an increase in injection efficiency in the QW.

Investigation of SiC MOSFET Body Diode Reverse Recovery and Snappy Recovery Conditions

This paper investigates the behavior of SiC MOSFETs body diode reverse recovery as a function of different operating conditions. The knowledge of their effects is crucial to properly designing and driving power converters based on SiC devices, in order to optimize the MOSFETs commutations aiming at improving efficiency. Indeed, reverse recovery is a part of the switching transient, but it has a significant role due to its impact on recovery energy and charge. The set of different operating conditions has been properly chosen to prevent or force the snappy recovery of the device under testing. The experimental results and specific software simulations have revealed phenomena unknown in the literature. More specifically, the analysis of the reverse recovery charge, Qrr, revealed two unexpected phenomena at high temperatures: it decreased with increasing gate voltage; the higher the device threshold, the higher the Qrr. TCAD-Silvaco (ATLAS v. 5.29.0.C) simulations have shown that this is due to a displacement current flowing in the drift region due to the output capacitance voltage variation during commutation. From the analysis of the snappy recovery, it has emerged that there is a minimum forward current slope, below which the reverse recovery cannot be snappy, even for a high current level. Once this current slope is reached, Qrr varies with the forward current only.

Ultra-Thin GaAs Single-Junction Solar Cells for Self-Powered Skin-Compatible Electrocardiogram Sensors.

GaAs thin-film solar cells have high efficiency, reliability, and operational stability, making them a promising solution for self-powered skin-conformal biosensors. However, inherent device thickness limits suitability for such applications, making them uncomfortable and unreliable in flexural environments. Therefore, reducing the flexural rigidity becomes crucial for integration with skin-compatible electronic devices. Herein, this study demonstrated a novel one-step surface modification bonding methodology, allowing a streamlined transfer process of ultra-thin (2.3µm thick) GaAs solar cells on flexible polymer substrates. This reproducible technique enables strong bonding between dissimilar materials (GaAs-polydimethylsiloxane, PDMS) without high external pressures and temperatures. The fabricated solar cell showed exceptional performance with an open-circuit voltage of 1.018V, short-circuit current density of 20.641mAcm-2, fill factor of 79.83%, and power conversion efficiency of 16.77%. To prove the concept, the solar cell is integrated with a skin-compatible organic electrochemical transistor (OECT). Competitive electrical outputs of GaAs solar cells enabled high current levels of OECT under subtle light intensities lower than 50mWcm-2, which demonstrates a self-powered electrocardiogram sensor with low noise (signal-to-noise ratio of 32.68dB). Overall, this study presents a promising solution for the development of free-form and comfortable device structures that can continuously power wearable devices and biosensors.

FPGA-Based VFF-RLS Algorithm for Battery Insulation Detection in Electric Vehicles

As the adoption of electric vehicles (EVs) continues to rise, attention has switched to ensuring the safety of EV operations. The exponential growth in battery technology over the past several years has changed the face of energy storage and sparked a revolution in several industries. The degradation of battery insulation during regular use is a significant concern. The high voltage (HV) and current levels in HV electric vehicles pose a significant electrical threat.The advancement of electric vehicle technology has led to an increasing presence of HV electric equipment throughout the vehicle. The insulation strength and early health status detection of the batteries are essential in ensuring safety in EVs. This paper studies the different insulation detection techniques and the development of adaptive filter (AF) algorithms based on field-programmable gate arrays (FPGAs) for insulation detection. FPGAs are amongst the most accurate and fast detection techniques among all the insulation detection techniques used so far in electric vehicles. This study proposes an FPGA-based VFF-RLS algorithm for effectively implementing insulation detection in EVs. The experimental test results using FPGAs demonstrate that the proposed method can rapidly monitor changes in insulation resistance (IR). The VFFRLS-based FPGA technique works sufficiently well to reduce errors when dealing with variations in voltage and resistance conditions at the battery terminals.

Improved electrochemical performance of fast-charging Li-S batteries with constant power transfer protocol

Reducing the time required to replenish depleted energy in batteries stands as a crucial milestone to propel further advancements in electric vehicles and related applications. Traditional charging procedures pose notable challenges, particularly the reduction in battery capacity observed at higher current levels. In the pursuit of novel rapid protocols, certain approaches have been devised and implemented. However, their feasibility, practicality, and specific technological advantages remain unclear. In this study, we conduct a comparative analysis, for the first time, of the electrochemical performance of promising lithium‑sulfur batteries. We assess the use of an unconventional fast charging protocol involving constant power transfer against the outcomes derived from employing the conventional constant current protocol under similar conditions. The constant power charging protocol proves highly effective for rapid charging rates (ranging from 1C to 4C), resulting in over a 10 % reduction in charging duration compared to the conventional CC protocol. Additionally, it significantly decreases overall degradation per cycle by up to 46.67 % and noticeably enhances cell lifespan, all while maintaining the same energy consumption during the charging process. The observed differences in behavior provide valuable insights into the mechanisms through which the constant power protocol enhances electrochemical performance.

Improvement of AlGaN/ GaN based HEMT with high performance rate for integrated circuit design for wide range of applications

In the current research work, we focused on the design and analysis of a semiconductor device called High-Elec-tron-Mobility Transistor (HEMT) based on the AlGaN/GaN material system. An Aluminum Nitride spacer,Layer of Nucle-ation along with cap as a AlGaN and barrier of GaN with the channel of AlGaN are incorporated to enhance HEMT device performance.The electrical characteristics of the proposed HEMT are an-alyzed. The Drain Current is found to be 0.18A/mm, indicating the device's ability to handle high current levels. The Electron Concentration is observed to have a maximum value of -96.12electrons/cm3 and varying based on the position in the channel for GaN Barrier thickness is 0.15mm. In the analysis of AC such as Gain of the Maximum Unilateral Power is deter-mined to be 83.41dB, indicating the ability of the device to am-plify signals. The Y-parameters, which characterize the de-vice's behavior at various frequencies of operation, are also de-termined. The capacitance between the electrode region Gate-Source (CGSMIN) is found to be 1.70×10^-11 F/mm, and alike The Capacitance between the electrode region the Gate-Drain Ca-pacitance (CGDMIN) is determined to be 4.7×10^-12 F/mm. Fur-thermore, an Electric Field of 96.51×10^3 V/mm is observed, in-dicating the strength of the electric field across the device. For HEMT device the simulation,The TCAD Silvaco software is be-ing practiced.

Modelling and simulation of MR damper characterization and uncertainty assessment in marine engine vibration isolation with FLPID control

ABSTRACT This paper meticulously examines the magneto-rheological (MR) damper to exploring its application in a semi-active isolator system. The MR damper’s distinctive capability to regulate damping force through an externally applied magnetic field is investigated via extensive experimental testing. Sinusoidal displacement inputs with varying electromagnet currents reveal a direct correlation between higher current levels and augmented MR damper forces. Validation of the experimental results is achieved through the Viscous Plus Dahl Model, showcasing its accuracy in capturing the damper’s hysteresis behavior. The study extends its scope to practical implementation by integrating the MR damper into a marine diesel engine system. A fuzzy logic-based self-tuning PID controller collaborates with the MR damper to establish a semi-active vibration isolator. The integrated model, encompassing primary and secondary masses, the engine, and the isolator with passive and semi-active systems, is rigorously analyzed. Experimental validation and theoretical simulations, aligned with data gathered from experiments, affirm the model’s fidelity in representing the MR damper. Simulation outcomes underscore the significant enhancement in vibration reduction characteristics of the semi-active isolator system compared to its passive counterpart, particularly evident in the improved performance of the 1200 kg engine under diverse operating conditions.

Constructing blocked-nanolayer by surface charge inversion over anion exchange membrane for improved antifouling performance

Anion exchange membranes (AEMs) with excellent antifouling property are essential for treating highly saline organic wastewater through electrodialysis (ED). In this study, we proposed a strategy of surface charge inversion to construct a blocked- nanolayer based on in-suit dopamine (DA) deposition followed by grafting negative-charged 2-acrylamide-2-methylpropanesulfonic acid (AMPS) for promoting the antifouling performance of AEM. It's indicated that the surface hydrophilicity and negative charge density was gradually enhanced with the increase of AMPS grafting density without sacrifices of ion exchange capability, swelling ratio and desalination performance. In the simulated fouling experiments, the optimal AEM-AMPS-105 membrane exhibited excellent antifouling property due to the improved surface hydrophilicity and high electrostatic repulsion against organic matter. It's highlighted that the transmembrane voltage of modified membrane after operating 200 min was reduced from 7.12 V to 4.85 V with a significant decrease of energy consumption by 55.1 % while maintaining a high current efficiency level of 85.5 %. Moreover, the modified membrane performed significantly enhanced salt/contaminant selectivity and high stability in dye wastewater treatment. We anticipated that the construction of charge-blocked nanolayer by surface charge inversion offered a practical method for improving the organic fouling-resistance of AEMs.

Modelling and Analysis of Electromechanical Stress in Transformers Caused by Short-Circuits

A common reason for internal faults in transformers windings is the weakness insulation caused by vibration / deformation related to electromechanical forces produced by high short circuit currents. This phenomenon significantly reduces the transformer life expectancy and may even lead to its instantaneous or timing destruction. Focusing this subject this paper is aimed at presenting the performance of a time domain model inserted in a finite element program i.e. the 3D software package and the investigation of the relationship between high current levels occurring at transformer windings and the internal mechanical stresses. To highlight the overall model and the software performance, a laboratory 15 kVA transformer is utilized to show the programme facilities and potentially. The transformer has been built with concentric double-layer windings and ferromagnetic core with three columns and this equipment has been submitted to a balanced three-phase short- circuit. In addition, the computational simulations were carried out using distinct geometries to the windings i.e. with and without deformation.

Vulnerability of the rip current phenomenon in marine environments using machine learning models

Hidden and perilous rip currents are one of the primary factors leading to drownings of beach swimmers. By identifying the coastal areas with the highest likelihood of generating rip currents, it becomes possible to prevent fatalities and mitigate economic losses associated with these hazardous currents. Rip currents are characterized as streams of water moving towards the open sea, forming within the area where waves break, due to variations in wave-induced radiation stresses and pressure along the coastline. This study utilized nine different Machine Learning (ML) models, including M5 Model Tree (MT), Multivariate Adaptive Regression Spline (MARS), Gene Expression Programming (GEP), Evolutionary Polynomial Regression (EPR), Random Forest (RF), Support Vector Machine (SVM), Extreme Gradient Boosting (XGBoost), Adaptive Boosting (AdaBoost), and Stacked ML models, to estimate the Relative Tide Range (RTR) values for 50 southern beaches in China. Through this approach, we gathered a reliable dataset from prior research conducted on the southern coast of China. In this study, two parameters, namely dimensionless fall velocity parameter (Ω) and tide range (TR) are used to predict the vulnerability of rip current event. The results of the AI models were assessed by various statistical analyses (Correlation of Coefficient [R], Root Mean Square Error [RMSE], violin diagram, heatmap, and taylor diagram) for training and testing stages. Accordingly, the MARS model exhibited superior performance compared to other AI models in accurately predicting the RTR value. The outcomes substantiated the significant effectiveness and capability in estimating the RTR with high accuracy. Southern China coasts have relative high risk level of rip current, necessitating the attention and strategic management of this dangerous current by the beach managers.

Some data on status of the herd of horsehair crab (<i>Erimacrus isenbeckii</i>) in the northwestern Tatar Strait

The data of trap surveys and observations aboard fishing vessels conducted in the northwestern Tatar Strait (northward from Cape Zolotoy) in 2009–2022 are analyzed. Horsehair crabs dwell along the entire continental coast from Cape Zolotoy in the south to Cape Nakatov in the north, but commercial aggregations with the density on average 232 ind./km2 are concentrated in the southern part of this area (south of 49о N). Seasonal bathymetric migrations of the crab include the fall moving of commercial males from the depths of 10–40 m to the depths of 40–60 m for wintering and their return to shallows in spring. Two dense wintering aggregations are formed usually between Cape Peschany – Cape Mapatsa and southward from 48о00′ N, whereas sparse summer aggregations are widely distributed along the coast. Regardless the season, the aggregations density decreases from south to north. The males are generally larger in the southern aggregations than in the northern ones (on average, 100.3 and 89.8 mm of carapace width, respectively), the difference is statistically significant (p < 0.0001). The stock of horsehair crab in the northwestern Tatar Strait has increased in the last 20 years from136 tons in 2003 to 1580 tons in 2022. Over the past 10 years, the optimal allowable catch in the Primorye subzone north of Cape Zolotoy was utilized less than 50 %. There is no specialized fishery of horsehair crab; the species is caught mainly as bycatch for other shelf crab species. High current level of the stock gives a good background for commercial removal of at least 158 t of horsehair crab without damage to the local population of this species.

(Invited) Leading-Edge Diamond FET, MEMS, and Photodetector Devices

Diamond is a candidate material for next-generation power electronics, micro-electro mechanical systems (MEMS), and solar-blind deep-ultraviolet (DUV) photodetector devices with excellent thermal stability and radiation hardness, which operate under extreme environment. In order to use an advantage of high-density hole channel of hydrogenated diamond (H-diamond) surface, we have developed the high-k stack gate dielectrics and AlN heterojuction gate for H-diamond FETs, such as HfO2/HfO2, LaAlO3/Al2O3 Ta2O5/Al2O3, and ZrO2/Al2O3, AlN/Al2O3 prepared by a combination of sputter-deposition (SD) and atomic layer deposition (ALD) techniques [1,2]. We also demonstrated the artificial diamond Fin-FETs with high-current level [3] and the nanolaminate insulator gate metal-oxide-gate FETs (MOSFETs) with k value as high as 100 [4], and the new transistor concept named by metal-insulator-metal-semiconductor field-effect transistor (MIMS-FET) to achieve normally-off operation by combining the advantages of MOSFET and metal-semiconductor FET [5]. In addition, we developed the routine ion-implantation process for preparing the diamond cantilever with a resonant frequency quality factor as high as one million [6,7]. We have also developed thermally stable Schottky barrier photodiode (SPD), metal-semiconductor-metal photodetector (MSMPD), and MSM-type SPD (IDF-SPD) with a large photoconductivity gain in DUV wavelength and a large discrimination ratio between DUV/visible light responsivity [8,9]. In this presentation, we will review the comprehensive our work on the diamond FET, MEMS, and photodetector devices. Acknowledgements: This work was in collaboration with J-W. Liu, M. Imura, M-Y. Liao, J. Alvarez in NIMS and A. Ouchiero and E. Obaldia in University of Taxes, Dallas, and partly supported by JSPS KAKENHI Grant Number 20H00313.

An Accurate Electro-Thermal Coupling Model of a GaAs HBT Device under Floating Heat Source Disturbances.

Taking into consideration the inaccurate temperature predictions in traditional thermal models of power devices, we undertook a study on the temperature rise characteristics of heterojunction bipolar transistors (HBTs) with a two-dimensional cross-sectional structure including a sub-collector region. We developed a current-adjusted polynomial electro-thermal coupling model based on investigating floating heat sources. This model was developed using precise simulation data acquired from SILVACO (Santa Clara, CA, USA). Additionally, we utilized COMSOL software (version 5.6) to simulate the temperature distribution within parallel power cells, examining further impacts resulting from thermal coupling. The research findings indicate that the rise in current induces modifications in the local carrier concentration, thereby prompting variations in the local electric field, including changes in the heat source's peak location and intensity. The device's peak temperature exhibits a non-linear trend regulated by the current, revealing an error margin of less than 1.5% in the proposed current-corrected model. At higher current levels, the drift of the heat source leads to an increase in the heat dissipation path and reduces the coupling strength between parallel devices. Experiments were performed on 64 GaAs (gallium arsenide) HBT-based power cells using a QFI infrared imaging system. Compared to the traditional temperature calculation model, the proposed model increased the accuracy by 6.84%, allowing for more precise predictions of transistor peak temperatures in high-power applications.

High inductance magnetic-core coils have enhanced efficiency in inducing suprathreshold motor response in rats

Objective. Transcranial magnetic stimulation (TMS) coil design involves a tradeoff among multiple parameters, including magnetic flux density (B), inductance (L), induced electric (E) field, focality, penetration depth, coil heating, etc. Magnetic materials with high permeability have been suggested to enhance coil efficiency. However, the introduction of magnetic core invariably increases coil inductance compared to its air-core counterpart, which in turn weakens the E field. Our lab previously reported a rodent-specific TMS coil with silicon steel magnetic core, achieving 2 mm focality. This study aims to better understand the tradeoffs among B, L, and E in the presence of magnetic core. Approach. The magnetic core initially operates within the linear range, transitioning to the nonlinear range when it begins to saturate at high current levels and reverts to the linear range as coil current approaches zero; both linear and nonlinear analyses were performed. Linear analysis assumes a weak current condition when magnetic core is not saturated; a monophasic TMS circuit was employed for this purpose. Nonlinear analysis assumes a strong current condition with varying degrees of core saturation. Main results. Results reveal that, the secondary E field generated by the silicon steel core substantially changed the dynamics during TMS pulse. Linear and nonlinear analyses revealed that higher inductance coils produced stronger peak E fields and longer E field waveforms. On a macroscopic scale, the effects of these two factors on neuronal activation could be conceptually explained through a one-time-constant linear membrane model. Four coils with different B, L, and E characteristics were designed and constructed. Both E field mapping and experiments on awake rats confirmed that inductance could be much higher than previously anticipated, provided that magnetic material possesses a high saturation threshold. Significance. Our results highlight the novel potentials of magnetic core in TMS coil designs, especially for small animals.

Temperature Dependence of Low‐Frequency Noise Characteristics of NiOx/β‐Ga2O3 p–n Heterojunction Diodes

AbstractTemperature dependence of the low‐frequency electronic noise in NiOx/β‐Ga2O3 p–n heterojunction diodes is reported. The noise spectral density is of the 1/f‐type near room temperature but shows signatures of Lorentzian components at elevated temperatures and at higher current levels (f is the frequency). It is observed that there is an intriguing non‐monotonic dependence of the noise on temperature near T = 380 K. The Raman spectroscopy of the device structure suggests material changes, which results in reduced noise above this temperature. The normalized noise spectral density in such diodes is determined to be on the order of 10−14 cm2 Hz−1 (f = 10 Hz) at 0.1 A cm−2 current density. In terms of the noise level, NiOx/β‐Ga2O3 p–n diodes perform excellently for new technology and occupy an intermediate position among devices of various designs implemented with different ultra‐wide‐bandgap semiconductors. The obtained results are important for understanding the electronic properties of NiOx/β‐Ga2O3 heterojunctions and contribute to the development of noise spectroscopy as the quality assessment tool for new electronic materials and device technologies.

Early failure of high-power white LEDs for outdoor applications under extreme electrical stress: Role of silicone encapsulant

Solid state lighting systems have deeply penetrated the market and are widely available. White light emitting diodes (LEDs) are based on a gallium nitride blue-emitting chip and a phosphor-based layer is used to convert blue radiation to white light, in combination with an optical system to enhance light extraction. High temperatures can be detrimental for LED reliability, resulting in a gradual or catastrophic failure. Therefore, the design of such devices, especially in relation to use cases that require operation at high current and temperature levels, needs to be based on reliability considerations.In this work we analyze the robustness of high power white LEDs submitted to driving currents exceeding the nominal levels by means of electrical and optical characterization, as well as on failure analysis techniques. The results highlight a significant degradation of the main optical parameters (luminous flux, color coordinates, correlated color temperature, …). Device cross sectioning highlighted a heavy darkening of the silicone material in the overstressed devices, and a delamination of the phosphors. Raman spectroscopy analysis highlighted an enhancement in luminescence of degraded samples. Such degradation was ascribed to the high temperature reached by the LEDs during the stress, that caused the degradation of the silicone lens; the process can be enhanced by the low efficiency of the phosphors and LEDs at high temperatures, resulting in a stronger heating of the devices.