High Power LED Research Articles

Luminescence-Tunable High-Power White Light-Emitting Diodes Through Dam-Adjusted Ceramic Substrate

In this work, luminescence-tunable high-power white light-emitting diodes (WLEDs) were fabricated by printing phosphor-in-silicone on 3-D ceramic substrates with adjusted dam structure. The 3-D ceramic substrate was prepared by a simple and efficient magnetic field-oriented grouting method in which silicate ceramic dam with adjusted height and angle was reliably bonded on a planar direct plating ceramic (DPC) substrate. The phosphor concentration of WLEDs was optimized to realize white light. At the phosphor concentration of 12 wt%, the packaged WLEDs achieve cool white light and high optical consistency. The influence of dam height and angle on the optothermal performances of WLEDs was investigated. As the dam height increases from 0.5 to 1.0 mm, the luminous efficiency (LE) of WLEDs first increases and then decreases, and the correlated color temperature (CCT) gradually decreases. At the dam height of 0.7 mm, the WLED achieves a high LE of 122 lm/W and a suitable CCT of 5008 K. Furthermore, the LE increases from 122 to 132 lm/W and the CCT decreases from 5006 to 4458 K when the dam angle changes from 0° to 40°. Importantly, the dam height and angle have no obvious influence on the surface temperature of WLEDs, and the WLEDs still display a low surface temperature even at high input current due to the effective heat dissipation of dam structure. The results indicate that the fabricated WLEDs achieve the tunable luminescence and low working temperature, which can be treated as an efficient and reliable high-power white source.

Modulation of the carrier balance of lead-halide perovskite nanocrystals by polyelectrolyte hole transport layers for near-infrared light-emitting diodes

An alternative material, methylamine (MA)-doped poly[3-(4-carboxymethyl)thiophene-2,5-diyl] (P3CT) as hole transport layer (HTL) was investigated for efficient solution-processed near-infrared perovskite light-emitting diodes (NIR PeLEDs). The best NIR PeLEDs performance was achieved with an optimized composition ratio of the MA-doped P3CT (1:1) due to the balance of the electron and hole carrier in the active layer. The charge-balanced NIR PeLEDs exhibit the highest radiance of 858.37 W sr−1 m−2, a low turn-on voltage of 1.82 V, and an external quantum efficiency of 7.44%. Our findings show that using P3CT as an alternative HTL has the potential to significantly improve PeLED performance, allowing it to play a role in the development of practical applications in high-power NIR LEDs.

Fibers-induced segregated-like structure for polymer composites achieving excellent thermal conductivity and electromagnetic interference shielding efficiency

With the rapid development of new-generation wireless communication technologies and portable intelligent electronic devices, the development of composites with excellent thermal conductivity and electromagnetic shielding properties has become an urgent challenge. In this work, a unique fibers-induced segregated-like structure strategy for fabricating thermoplastic polyurethane/polydopamine/silver (TPU/PDA/Ag) composites film with high thermal conductivity (TC) and excellent electromagnetic interference (EMI) shielding performance is demonstrated via electrospinning-electroless depositing-pressing technology. The TPU/PDA/Ag composites film exhibit excellent in-plane TC of 20.9 W/(m⋅K) at 75 wt% Ag loading, which shows excellent thermal management capability as heat spreaders of high-power light-emitting diode (LED) modules in practice. Meanwhile, the composites film presents outstanding EMI shielding efficiency of 109 dB (8.2–12.4 GHz) with a thickness of 45 μm and prominent EMI shielding reliability after 1000 cycles of bending. In addition, the composites film shows good tensile strength (12.1 MPa), elongation at break (108.0%), and toughness (11.59 MJ/m3). The obtained TPU/PDA/Ag composites film achieves the desired balance among thermal conductivity, EMI shielding, and mechanical properties, indicating broad application prospects in new-generation wireless communication technologies and portable intelligent electronic devices.

Utilization of High-Power Leds as Non-Invasive KV Meter Detectors in Collimation of Lighting

X-ray radiation is used to diagnose the human body. Two parameters are often used as settings when using this machine. The first is the KV value, and the second is the mA value. If an error occurs in the kV setting, it will cause inappropriate image quality, so that it will provide inaccurate information in patient examination. Likewise with the presence of excessive doses to the patient's body. To ensure that the KV value that comes out is in accordance with the settings on the machine consul, invasive and non-invasive measurements can be carried out. Non-invasive is becoming an easy standard to do. Several types of equipment on the market and research results have been widely used for this non-invasive activity. The problem is that currently the existing tools still use detectors at an expensive price. The purpose of this study was to design a low-cost non-invasive x-ray KVmeter detector using an LED detector and test the ability of the detector at each point of collimation.. The method used in this study is to stump the detectors placed at 4 ends of the collimation 20 cm apart. The data is taken by doing x-ray exposure at a distance of 60 cm. The module measurements were carried out under 80 mA exposure conditions for 1 second and a collimation area of ​​20 x 20 cm. X-ray exposure settings were performed at 40kV, 50kV, 60kV, and 70kV settings. The module measurement results are compared with the x-ray machine setting values. From the comparison results, the smallest error rate on Sensor 2 is 0.83% while the highest error is on S5 of 26.43%. The results can be concluded that the LED phosphor can capture x-rays, but the detector is weak due to interference from ambient light. The results obtained from the detector itself are still less stable and linear. In future research, stability and linearity will be built using a mechanical design that reduces ambient light interference.

Current Trends in Wick Structure Construction in Loop Heat Pipes Applications: A Review.

Thermal control systems have been introduced as an important part of electronic devices, enabling thermal management of their electronic components. Loop heat pipe (LHP) is a passive two-phase heat transfer device with significant potential for numerous applications, such as aerospace applications, high-power LEDs, and solar central receivers. Its advantages are high heat transfer capability, low thermal resistance, long-distance heat transfer, and compact structure. The essential role of wick structures on the performance of LHPs has already been highlighted, but no comprehensive review is available that deals with different parameters such as LHP design and wick size, which are largely decisive and effective in achieving a practical level of thermal transmission governed by wick structures. To rely on this necessity, this article summarizes, analyzes, and classifies advancements in the design and fabrication of wick structures. The main conclusion to be drawn after careful monitoring and weighing of the related literature is that LHPs with composites and additively manufactured wicks show a higher heat transfer coefficient than other conventional structures. Indeed, future works should be focused on the design of more structurally efficient wicks, which may allow us to optimize materials and geometrical parameters of wick structure for higher heat transfer through LHPs.

Structural Optimization of Vertically-Stacked White LEDs with a Yellow Phosphor Plate and a Red Quantum-Dot Film.

A remote-type white light-emitting diode (LED) consisting of a red quantum-dot (QD) film and a yellow phosphor plate was studied by both experiment and optical simulation. The sequence of the two color-conversion films had a substantial effect on the color-rendering properties of the vertically-stacked white LED, and the optimized configuration exhibited a high color rendering index of more than 90 thanks to the enhanced red component via the QD film. For the design of high-power white LED devices of a remote type, it was necessary to locate the color-conversion films below the diffuser plate to remove the substantial color dispersion depending on the viewing angle. The present study shows that high power and high color-rendering white LED devices can be realized in terms of two vertically-stacked color-conversion materials, which would provide long-term stability due to the remote design.

Tailored carbon-based aramid nanofiber nanocomposites with highly anisotropic thermal conductivity and superior mechanical properties for thermal management

Polymer nanocomposites show great potential as thermal management materials owing to their light weight and high design freedom. However, they often suffer from the inability of integrating a high thermal conductivity, satisfactory mechanical properties, and even elevated temperature resistance for real-world scenarios. Here we tailor high-performance carbon-based aramid nanofiber (ANF) nanocomposites toward highly anisotropic thermal conductivity and superior mechanical properties through a vacuum-filtration-induced self-assembly process. The as-obtained ANF nanocomposite films exhibit a unique hierarchical structure composed of horizontally stacked carbon fillers in the ANF matrix, thereby achieving a high in-plane thermal conductivity of 20.54 Wm−1K−1 at only 20 wt% graphene nanosheet loading and anisotropy factors of over 100. Further finite element simulations and proof-of-concept applications for high-power light-emitting diode chip cooling demonstrate the excellent heat dissipation performance of the resulting nanocomposite film. More importantly, the tailored ANF nanocomposite films exhibit high mechanical robustness, high flexibility, superb thermal stability, and flame retardancy, making them extremely promising for thermal management applications in various electronic devices.

A 3D printed photoreactor for investigating variable reaction geometry, wavelength, and fluid flow.

Research in the field of photochemistry, including photocatalysis and photoelectrocatalysis, has been revitalized due to the potential that photochemical reactions show in the sustainable production of chemicals. Therefore, there is a need for flexible photoreactor equipment that allows for the evaluation of the geometry, light wavelength, and intensity of the vessel, along with the fluid flow in various photochemical reactions. Light emitting diodes (LEDs) have narrow emission spectra and can be either pulsed or run continuously; being flexible, they can be arranged to fit the dimensions of various types of the reactor vessel, depending on the application. This study presents a 3D printed photoreactor with the ability to adjust distances easily and switch between high-power LED light sources. The reactor design utilizes customized printed circuit boards to mount varying numbers and types of LEDs, which enables multiple wavelengths to be used simultaneously. These LED modules, comprised of heat sinks and cooling fans, fulfill the higher heat dissipation requirements of high-power LEDs. The flexibility of the reactor design is useful for optimizing the reaction geometry, flow conditions, wavelength, and intensity of photochemical reactions on a small scale. The estimates for incident light intensity under five possible reactor configurations using ferrioxalate actinometry are reported so that comparisons with other photoreactors can be made. The performance of the photoreactor for differing vessel sizes and distances, in both the flow and batch modes, is given for a photochemical reaction on 2-benzyloxyphenol-a model substance for lignin and applicable in the production of biobased chemicals.

Durability of the optical plastic polycarbonate under modulated blue LED irradiation at different duty cycles

In order to provide longer LED lifetimes, all LED-related components, including lenses and other optical components, need to be adapted to increasing radiation levels. Pulse width modulation (PWM) is an easy-to-implement method for driving and dimming LEDs and could be a cost-effective way to extend the lifetime of optical components installed in conjunction with the LED. In this study, polycarbonate (PC) samples were artificially aged with high-power blue LEDs using different driving modes in a newly developed test setup. The LEDs were pulse-width modulated in three different modes (50% duty cycle, 25% duty cycle, and continuous wave (CW)), while emitting the same optical power. Optical light microscopy, UV/vis spectroscopy, FTIR spectroscopy and gel permeation chromatography were performed to measure transmittance changes and general aging effects of the samples. The results indicate a substantial correlation of aging with the mode of exposure. It is found that the samples age most severely under CW irradiation, as both the decrease in transmission (at 295 nm wavelength, after 1500 h) and the sample temperature, and thus the degradation, are highest. FTIR spectroscopy showed the expected results for optical aging under LED irradiation, again the changes tended to be more pronounced for the samples irradiated without PWM. Gel permeation chromatography shows a decrease in the weight averaged molar mass, once more with the CW irradiated samples exhibiting the most significant decrease. However, optical light microscopy did not reveal any significant aging effects on the sample surface. Overall, modulation of the LED, and in particular a reduction of the duty cycle, has a positive effect on the durability of optical plastics at similar radiative energy loads. In order to explain the different aging behavior of the samples under the different driving modes, a model of the time-related temperature changes in the material during the heating phase at different duty cycles is proposed.

Observed Dust Devil-Like Flow Structures In Large-Scale Turbulent Rayleigh-Bénard Convection

Turbulent Rayleigh-Bénard (RB) convection, a fluid layer heated from below and cooled from above, might be an appropriate tool to reproduce flow phenomena as occurring in a convective atmospheric boundary layer. One of these phenomena is the appearance of so-called dust devils, vortex like flow structures with typical dimensions up to a few tens of meters in diameter and up to a few hundreds of meters in height. Unlike their big brothers, the tornados, start to evolve close to the ground, but the physics of their evolution are still not fully understood. Since field measurements of dust devils are extremely hard to realize (due to their very rare and spontaneous appearance at arbitrarily varying locations), continuous flow measurements in large-scale laboratory experiments may help to overcome this problem. Such measurements in flows of several m³ in volume require optical measurement techniques like particle tracking velocimetry which gains access to the 3-dimensional Lagrangian velocity field. Special attention has to be drawn to the particle seeding of the flow and the imaging of particles. Particles must have neutral density compared to the fluid, and must be large enough to be detected by cameras over a range of several meters. They also should exhibit a prolonged lifetime. In this study, we present experiments conducted in the “Barrel of Ilmenau”, the world-wide largest Rayleigh-Bénard laboratory experiment with 7.15 m in diameter and up to 6.3 m in height using air as working fluid. Neutrally-buoyant helium-filled soap bubbles were injected into the flow and tracked using four cameras. Illumination was carried out with five high-power LEDs in pulsed mode. Reconstruction of the Lagrangian velocity field was performed with Shake-The-Box algorithm. Thus, the major focus of the presented work was to get access to the entire volumetric Lagrangian velocity field in the convection cell on a very long time. Our aim is to discover very rare flow events in turbulent convection, like e.g. dust devil-like vortices or other turbulent superstructures. Measurement data was analyzed to conclude about the applicability of particle tracking velocimetry as suitable measurement technique for large volumetric flows. Finally, an example of a discovered dust-devil like vortex is presented in detail.

Optical and Electrical Considerations for Developing Pulsed High-Power LED for Volumetric Particle Tracking Velocimetry

Volumetric Particle Tracking Velocimetry (PTV) in volumes larger than 103 cm3 with 15 μm Air Filled Soap Bubbles (AFSB) requires a powerful pulsed laser source of few tenth of mJ pulse energy, depending on the optical arrangement of the experiment. Initial experiments in our lab with 15 μm AFSB and 1 mJ pulse energy from a 532 nm laser source showed that in order to image turbulence flow phenomena in volumes about 4x10^3 cm^3 at 1 m working distance and an f-number of 8, one would need a laser source with about 315 mJ pulse energy and 1260 W average power at 4 kHz repetition rate. Such high-power 532 nm lasers are not simple to build and are expensive and complicated to develop. By reducing the working distance and increasing the diameter of the camera aperture, the required laser power was reduced by a factor 18 to 17.5 mJ pulse energy and 70 W average power, which is still a very high power laser. As a possible alternative, we report here on the development of a collimated beam, high-power, pulsed 460 nm LED for volumetric PTV measurements of turbulence flow in a large volume seeded with AFSB p articles. We report of the optical and electrical consideration that are required in development of such an LED source. First, we combined a practical model for the output power of an LED with a model that estimates the signal level on a CMOS detector in a volumetric PTV experiment with AFSB particles. It predicted that our LED should be driven by 277 A in order to generate 1 mJ of optical pulse energy with 20 μs pulse duration. In order to avoid power drooping at high currents density in the LED, we chose an architecture of LEDs array where each LED unit of the array operates at 20 μs pulse duration, 4 kHz repetition rate and with peak current of 200 A. Each such LED will deliver 0.72 mJ pulse energy and 24 such LED units will supply the required optical density. Second, we report of the optical and electrical features of the collimated , high-power, pulsed 460 nm LED unit we built. We tested the LED in a PTV experiment where the LED operated with 0.72 mJ pulse energy, 1 kHz repetition rate and 20 A peak current. The measured signal current from a CMOS-pixel due to Mie scattering AFSB particles was in good agreement with the predicated signal level.

Measurement Of Aerodynamically Induced Blade Distortion On A Shrouded Counter-Rotating Prop-Fan

Blade deformation on a 1 m diameter composite fan rotor is measured simultaneously using stereoscopic image pattern correlation technique (IPCT) and blade-tip imaging. Absolute referencing of the blades is made possible by simultaneously tracking a marker on the hub using a fourth camera. Illumination is provided by microsecond pulses of high-power LEDs. Rise and fall time in the 100 ns regime are achieved using a self-designed high-current drive circuit. A high-speed microcontroller provides accurate, speed-independent angular delays to enable phase-locked triggering of cameras and LEDs. Mean and RMS deformation of the blade are acquired for different aerodynamic loading conditions induced by imposing a non-uniformity upstream of the rotor aimed at mimicking boundary layer ingestion.

Li+ doping induced zero-thermal quenching in Cs3Zn6–x–yB9O21:xEu3+,yLi+ (0 ≤ x ≤ 0.10, 0.06 ≤ y ≤ 0.16)

Thermal stability is a crucial index to assess application value of high-power LEDs, which is related to lattice defects. Herein, an effective structure-engineering strategy is proposed to achieve excellent properties. Under the 394 nm excitation, Cs3Zn5.94B9O21:0.06Eu3+ possesses two characteristic emissions peaked at 591 and 612 nm with limited thermal stability. By introducing Li+ ions into the lattice, the sample exhibits high color purity and excellent zero-thermal quenching because the defect contents of the phosphor can be effectively modulated via charge-compensation effect. Then, under the stimulus of high temperature, the corresponding trap levels with a suitable depth (E = 1.27 eV) will release electrons to recombine with the luminescent centers, compensating for the energy loss. The study provides a meaningful guide for optimizing and designing novel functional photoluminescent materials.

A Newly Developed Inverted Rotating Disk Electrode (IRDE) Setup for the Investigation of Photoelectrochemical Reactions

A new setup for an inverted rotating disk electrode (IRDE) was developed for the investigation of photoassisted or photoelectrochemical processes involving mass transfer reactions, as in electrodeposition or etching processes. In this setup, rotation of the disk electrode is achieved by magnetic coupling between a driver magnet (i.e. a magnetic stirrer) and the follower magnet included in the sample holder. For photoelectrochemical experiments, the cell allows a homogeneous illumination and removal of gaseous reaction products, while still providing leak tightness. In this way, controlled flow conditions are provided with the possibility to simultaneously illuminate the sample surface from a distance as small as 20 mm. At the same time gases formed during the reaction can easily ascend through the electrolyte.The light source is placed on top of the cell and illumination is done through the electrolyte. A low liquid level (≥ 15 mm) allows a small distance between the sample and the light source and therefore a high light intensity on the sample surface. Illumination is done using a high-power LED. Due to the high power, thermal effects need to be taken into consideration and especially an effective cooling of the LED is essential.As a wide band gap semiconductor, silicon carbide (SiC) has gained large interest due to its high chemical and physical stability. Since photoassisted anodic etching of n-type 4H silicon carbide in potassium hydroxide solutions [1] requires both UV illumination and the removal of gaseous reaction products, this reaction is investigated in the newly developed IRDE setup. Possible applications for such a process are defect decoration [2], trench etching, and dicing.Photoassisted anodic etching of n-type SiC occurs in three steps: (1) hole generation in the material through illumination with light with an energy higher than the bandgap of the semiconductor (2) oxidation of silicon and carbon through the holes driven to the semiconductor-electrolyte interface by an external potential and (3) dissolution of the oxidation products in the electrolyte. In accordance with the three steps of the reaction, different processes can be limiting: For low light intensities (either through a large distance between the sample and the LED or through low driving currents through the LED) the number of photon-induced holes is limiting. At low electrolyte concentrations, the transport of hydroxyl ions and the dissolution of the oxidation products determine the etch rate. For high light intensities and high electrolyte concentrations, the external potential and thereby the oxidation reaction are limiting for the overall current flow. These different reaction regimes can be distinguished in cyclic voltammetry measurements in the newly developed IRDE cell.[1] D. H. van Dorp und J. J. Kelly, „Photoelectrochemistry of 4H–SiC in KOH solutions,“ Journal of Electroanalytical Chemistry, Bd. 599, Nr. 2, pp. 260-266, 2007.[2] J. L. Weyher, S. Lazar, J. Borysiuk und J. Pernot, „Defect-selective etching of SiC,“ physica status solidi, Bd. 202, Nr. 4, pp. 578-583, 2005. Figure 1

Continuous-flow CvFAP photodecarboxylation of palmitic acid under environmentally friendly conditions

The fatty acid photodecarboxylase from Chlorella variabilis NC64A (CvFAP) promotes the elimination of CO2 from fatty acids (Cn) producing the corresponding hydrocarbon (Cn-1). Therefore, this enzyme is of great biotechnological interest since it can be used in alternative biofuel production routes matching the concept of green chemistry. However, due to its recent discovery, this reaction still requires optimizations, which was the focus of the present work together with the application of continuous flow system. The results in batch reactors showed the importance of using high power LED lamps (300 W) to reduce the reaction time for full conversion (30 min, >99%). In another approach, a continuous flow system demonstrated high potential, as it enabled full conversion with a half concentration of enzyme extract in a very short residence time of 15 min. Furthermore, the use of less expensive and sustainable light sources, not previously reported for reactions with CvFAP, were evaluated with full conversion (>99%) after 1 h for continuous flow reactions using 300 W common white LED lamp and based preliminary batch reactions investigations using direct sunlight. Thus, important advances and new perspectives for CvFAP photodecarboxylation reactions could be achieved with the present report.

Highly Parallelized, Multicolor Optogenetic Recordings of Cellular Activity for Therapeutic Discovery Applications in Ion Channels and Disease-Associated Excitable Cells.

Optogenetic assays provide a flexible, scalable, and information rich approach to probe compound effects for ion channel drug targets in both heterologous expression systems and associated disease relevant cell types. Despite the potential utility and growing adoption of optogenetics, there remains a critical need for compatible platform technologies with the speed, sensitivity, and throughput to enable their application to broader drug screening applications. To address this challenge, we developed the SwarmTM, a custom designed optical instrument for highly parallelized, multicolor measurements in excitable cells, simultaneously recording changes in voltage and calcium activities at high temporal resolution under optical stimulation. The compact design featuring high power LEDs, large numerical aperture optics, and fast photodiode detection enables all-optical individual well readout of 24-wells simultaneously from multi-well plates while maintaining sufficient temporal resolution to probe millisecond response dynamics. The Swarm delivers variable intensity blue-light optogenetic stimulation to enable membrane depolarization and red or lime-light excitation to enable fluorescence detection of the resulting changes in membrane potential or calcium levels, respectively. The Swarm can screen ~10,000 wells/day in 384-well format, probing complex pharmacological interactions via a wide array of stimulation protocols. To evaluate the Swarm screening system, we optimized a series of heterologous optogenetic spiking HEK293 cell assays for several voltage-gated sodium channel subtypes including Nav1.2, Nav1.5, and Nav1.7. The Swarm was able to record pseudo-action potentials stably across all 24 objectives and provided pharmacological characterization of diverse sodium channel blockers. We performed a Nav1.7 screen of 200,000 small molecules in a 384-well plate format with all 560 plates reaching a Z′ > 0.5. As a demonstration of the versatility of the Swarm, we also developed an assay measuring cardiac action potential and calcium waveform properties simultaneously under paced conditions using human induced pluripotent stem (iPS) cell-derived cardiomyocytes as an additional counter screen for cardiac toxicity. In summary, the Swarm is a novel high-throughput all-optical system capable of collecting information-dense data from optogenetic assays in both heterologous and iPS cell-derived models, which can be leveraged to drive diverse therapeutic discovery programs for nervous system disorders and other disease areas involving excitable cells.

Interstitial Li+ Occupancy Enabling Radiative/Nonradiative Transition Control toward Highly Efficient Cr3+-Based Near-Infrared Luminescence.

Highly efficient and stable broadband near-infrared (NIR) emission phosphors are crucial for the construction of next-generation smart lighting sources; however, the discovery of target phosphors remains a great challenge. Benefiting from the interstitial Li+ occupancy-induced relatively large distorted octahedral environment for Cr3+ and suppressed nonradiative relaxation of the emission centers, an NIR emission fluoride phosphor Na3GaF6:Cr3+,Li+ peaking at 758 nm with a high internal quantum efficiency of 95.8% and an external quantum efficiency of 38.3% is demonstrated. Moreover, it exhibits a good thermal stability (84.9%@150 °C of the integrated emission intensity at 25 °C) and excellent moisture resistance as well. A high-power light-emitting diode (LED) with a record watt-level NIR output (974.12 mW) and a photoelectric conversion efficiency of 20.9% is demonstrated by combining Na3GaF6:Cr3+,Li+ and a blue InGaN chip, and a special information encryption/decryption technology suitable for rapid and long-distance identification of machines is further presented based on this device. This study not only advances the development of efficient NIR emission phosphors for broadband NIR LEDs but also for NIR-related emerging applications and devices.

A super stable Near-Infrared garnet phosphor resistant to thermal Quenching, thermal degradation and hydrolysis

Near-infrared (NIR) light-emitting materials are crucial for night vision, in vivo-imaging, and secret codes. However, issues such as thermal quenching and chemical stability tend to significantly suppress the efficiency. In this work, we modify NIR-emitting phosphor Y3(Al,Mg)2(Al,Si)3O12:Cr3+ (YMAS:Cr3+) by substitution via 2[Al3+] → [Mg2+] + [Si4+] based on prototype Y3Al5O12:Cr3+. The YMAS:Cr3+ phosphor shows extraordinary optical performance and chemical stability, with 86–93% quantum yield (QY), 94% room temperature emission intensity at 150 °C, and almost no luminescent loss after 8 days in water and heating at 1000 °C. The substitution lifts the local symmetry, leading to a weak crystal field, spin-allowed 4T2→4A2 transition of Cr3+ in YMAS:Cr3+, and the higher efficiency and broadening emission spectra compared to the prototype Y3Al5O12:Cr3+ (QY = 16%) of spin-forbidden 2E→4A2 in the strong crystal field. Potential applications are demonstrated by using YMAS:Cr3+ in a high-power output light-emitting diode and luminescent ink. This work proposes the strategy via altering the local effect for improving luminescence properties, potentially stimulating further research on NIR-emitting materials.

Quantum efficiency of europium doped LaPO4 phosphors for UV sensing applications

The radiation conversion phenomenon is used for UV sensing applications with rare earth doped phosphors. This paper presents the results of structural and optical measurements of undoped and europium doped LaPO4 phosphors. LaPO4 phosphors with 1% mol, 2% mol, and 5% mol of europium were fabricated by the co-precipitation method. The effect of Eu3+ concentrations on the luminescence characteristics under UV LED excitation was investigated. The maximum quantum efficiency of luminescence (c.a. 82%) was obtained in sampled doped with 5% of europium. Full Text: PDF ReferencesM. Runowski, "Nanotechnologia – nanomateriały, nanocząstki i wielofunkcyjne nanostruktury typu rdzeń/powłoka", Chemik 68, 9, 766-775 (2014). DirectLink J. Zhou, J.L. Leano Jr., Z. Liu, D. Jin, K.-L. Wong, R.S. Liu, et al., "Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications", Small 14, 1801882 (2018). CrossRef Z. Li, Y. Zhang, G. Han, "Lanthanide-Doped Upconversion Nanoparticles for Imaging-Guided Drug Delivery and Therapy", Springer Series in Biomater. Sci. Eng. 6, 139-164, (2016). CrossRef M. Lin, Y. Zhao, S. Wang, M. Liu, Z. Duan, Y. Chen, et al., "Recent advances in synthesis and surface modification of lanthanide-doped upconversion nanoparticles for biomedical applications", Biotechnol. Adv. 30, 1551-1561 (2012). CrossRef H. Su, Y. Nie, H. Yang, D. Tang, K. Chen, T. Zhang, "Improving the thermal stability of phosphor in a white light-emitting diode (LED) by glass-ceramics: Effect of Al2O3 dopant", J. Eur. Ceram. Soc. 38, 2005-2009 (2018). CrossRef J. Huang, X. Hu, J. Shen, D. Wu, C. Yin, R. Xiang, et al., "Facile synthesis of a thermally stable Ce3+:Y3Al5O12 phosphor-in-glass for white LEDs", Cryst. Eng. Comm 17, 7079-7085 (2015). CrossRef R. Zhang, H. Lin, Y. Yu, D. Chen, J. Xu, Y. Wang, "A new-generation color converter for high-power white LED: transparent Ce3+:YAG phosphor-in-glass", Laser Photon. Rev. 8, 158-164 (2014). CrossRef B. Zheng, Y. Bai, H. Chen, H. Pan, W. Ji, X. Gong, et al., "Near-Infrared Light-Excited Upconverting Persistent Nanophosphors in Vivo for Imaging-Guided Cell Therapy", ACS Appl. Mater. Interfaces 10, 19514 (2018). CrossRef J. Qiao, G. Zhou, Y. Zhou, Q. Zhang, Z. Xia, "Divalent europium-doped near-infrared-emitting phosphor for light-emitting diodes", Nature Communications 10 (1), 5267 (2019). CrossRef V. Singh, A. Kumar, C. Mehare, H. Jeong, S. Dhoble, "UV/VUV excited photoluminescence of Tb3+ doped LaPO4 green emitting phosphors for PDP applications", Optik 206, 163733 (2020). CrossRef G. Han, Y. Wang, C. Wu, J. Zhang, "Hydrothermal synthesis and vacuum ultraviolet-excited luminescence properties of novel Dy3+-doped LaPO4 white light phosphors", Mat. Res. Bull. 44 (12), 2255-2257 (2009). CrossRef K. S. Gupta, P. S. Ghosh, M. Sahu, K. Bhattacharyya, R. Tewari, V. Natarajan, "Intense red emitting monoclinic LaPO4:Eu3+ nanoparticles: host–dopant energy transfer dynamics and photoluminescence properties", RSC Adv. 5, 58832-58842 (2015). CrossRef

Copper wick based loop heat pipe for thermal management of a high-power LED module

Contemporary high-power LED modules are subjected to severe thermal management challenges due to continuing miniaturization and increased heat flux levels. The thermal loads need to be effectively dissipated to improve module reliability by maintaining the junction temperature below 120 °C. The viability of a Loop Heat Pipe (LHP), with copper as the wick material, as a potential thermal management solution for a 200 W high-power LED module is demonstrated in this work. The investigation is conducted in two stages. Firstly, the thermal performance of the LHP is characterized by using different working fluids, and sink temperatures, to obtain the optimum working conditions, using a heater assembly mimicking the LED module. Subsequently, the LHP is integrated with an actual high-power LED module, and this thermo-mechanical demonstrator is then characterized under different real-time operating conditions. Complimentary 3D computational heat transfer simulations are carried out to estimate the LED junction temperature and visualize the thermal fields generated in the LED module. The results demonstrate the efficacy of the copper-methanol LHP design for successful thermal management of the high-power LED module dissipating over 100 W/cm2 (maintaining junction temperature below 120 °C for the 200 W nominal power LED module).