High Power LED Research Articles

Enhanced luminescence of CaO:Eu2+ red phosphor in glass for high-power warm LED

Highly emissive and stable red phosphors are vital for the warm Light Emitting Diode (LED). Herein, blue-light-excited CaO:Eu2+ red phosphors were prepared using the carbonation method, coupled with the double crucible carbon reduction technology. The addition of GeO2 and SnO2 significantly enhanced the photoluminescence (PL) intensity and quantum efficiency. Furthermore, a phosphor-in-glass (PiG) made from an improved luminescent CaO:Eu2+ was developed and utilized for LED applications. Such PiG samples considerably improved the stability of CaO:Eu2+ phosphors. The excellent stability, high color rendering index (Ra) value of 87.7 and low correlated color temperature (CCT) of 4469 K confirmed the resulting CaO:Eu2+-based PiG as a promising material for white light-emitting diodes (WLEDs).

A novel red-emitting InScW3O12:Eu3+ phosphor with anti-thermal-quenching performance for high-power WLED applications

A series of red-emitting InScW3O12:Eu3+ (ISWO:Eu3+) phosphors with anti-thermal-quenching performance were successfully synthesized by conventional solid-state reaction. The phase structure and luminescent properties of ISWO:Eu3+ were systematically studied. The photoluminescence excitation (PLE) spectrum showed that ISWO:Eu3+ phosphor can be effectively matched with commercial ultraviolet (UV), violet and blue light chips. The main emission peak of the phosphor was located at 613 nm, which was attributed to the electric dipole transition 5D0 → 7F2. Under the optimal excitation, the prepared ISWO:0.08Eu3+ phosphor showed excellent anti-thermal-quenching performance, its photoluminescence (PL) intensity at 180 °C reached 157.4 % of initial intensity at room temperature. At 465 nm excitation, it also exhibited the anti-thermal-quenching property and the PL intensity remained 115.1 % at 150 °C of that at room temperature. In situ XRD analysis revealed that the lattice contraction resulting in an increase in structural rigidity as the temperature rising, which caused the change of Eu3+ local environment and improved the PL intensity. Finally, a series of warm white LED devices under varying power density conditions with stable output were prepared using the red ISWO:0.08Eu3+ phosphor, indicating that the ISWO:Eu3+ phosphor with excellent anti-thermal-quenching performance has potential application prospects in high-power white light-emitting diodes (WLEDs).

Spectroscopic properties of red-emitting Sr0.9Na0.2ZrO3:Eu3+ phosphors with potential applications in lasers and LEDs

A range of Sr0.9-yNa0.2ZrO3: Eu3+ (SNEZ) nanocrystalline phosphors with high color purity and exceptional laser properties were synthesized using sol-gel technique. The samples were characterized for structural and spectroscopic properties using methods including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), diffuse reflectance spectroscopy, and photoluminescence (PL) spectroscopy. Structural analysis revealed orthorhombic phase with average crystallite size 28-19 nm, decreasing with increasing Eu3+ concentration. A low phonon energy of 455–495 cm−1 and wide (expanding) band gaps (5.0–5.3 eV) were obtained for the SNEZ phosphors. Under the excitation of 300 nm, the SNEZ phosphor emits strong red light at 614 nm, attributed to the 5D0 → 7F2 transition of the Eu3+ ion. Both XRD and Judd-Ofelt analysis revealed two sites for the Eu3+ ions. Additionally, the optimized SNEZ-7 phosphor achieves a PL internal quantum efficiency of 96 % under UV light at 300 nm excitation. Laser properties such as stimulated emission cross-section, gain bandwidth, branching ratio of the SNEZ phosphor is comparable to those of glasses, fluorides and other oxides for red light emitting laser applications. The CIE coordinate values of the synthesized red phosphor closely match those of commercially available red light-emitting phosphors, with a purity level of about 95 %. This suggests its suitability for various device applications, particularly in high-power white LEDs and lasers, as a red emitter.

Anisotropy of radiation-induced defects in Yb-implanted β-Ga2O3

RE-doped β-Ga2O3 seems attractive for future high-power LEDs operating in high irradiation environments. In this work, we pay special attention to the issue of radiation-induced defect anisotropy in β-Ga2O3, which is crucial for device manufacturing. Using the RBS/c technique, we have carefully studied the structural changes caused by implantation and post-implantation annealing in two of the most commonly used crystallographic orientations of β-Ga2O3, namely the (-201) and (010). The analysis was supported by advanced computer simulations using the McChasy code. Our studies reveal a strong dependence of the structural damage induced by Yb-ion implantation on the crystal orientation, with a significantly higher level of extended defects observed in the (-201) direction than for the (010). In contrast, the concentration and behavior of simple defects seem similar for both oriented crystals, although their evolution suggests the co-existence of two different types of defects in the implanted zone with their different sensitivity to both, radiation and annealing. It has also been found that Yb ions mostly occupy the interstitial positions in β-Ga2O3 crystals that remain unchanged after annealing. The location is independent of the crystal orientations. We believe that these studies noticeably extend the knowledge of the radiation-induced defect structure, because they dispel doubts about the differences in the damage level depending on crystal orientation, and are important for further practical applications.

MicroLED arrays—A perspective beyond displays

MicroLEDs, particularly when integrated with CMOS microelectronics, represent a significant advancement in nitride technology. While large-area, high-power LEDs for solid-state lighting have seen extensive optimization, microLEDs present unique fabrication and characterization challenges. Utilizing standard CMOS design and foundry services for silicon driver electronics, a new hybrid interconnect technology must be developed for chip–chip or wafer–wafer integration, necessitating much higher lateral resolution than current bonding technologies. Beyond display technology, microLED integration opens avenues for groundbreaking applications such as highly efficient nanosensors, miniaturized optical neuromorphic networks, and robust chip-based microscopy. This paper explores recent advancements in nitride/CMOS hybrid modules, providing an overview of current technologies and future possibilities in this dynamic field.

α-Sr2SiO4:Ce3+, Dy3+, Na+ phosphors with abnormal thermal quenching properties for solid-state lighting applications

There is urgent need of thermally stable phosphors for fabricating high-performance white light emitting diodes (LEDs). In this paper, Sr2SiO4:0.02Ce3+,xDy3+, (0.02+x)Na+ phosphors were successfully synthesized by the solid-state reaction method and their luminescence properties were studied. Phase analysis shows that single-phasic α-Sr2SiO4 was prepared when x was greater than 0.006, while a mixed phase of α-Sr2SiO4 and β-Sr2SiO4 were obtained in the samples with x of 0.006 or less. When excited at 344 nm, there is a major emission band at 380–500 nm corresponding to the 5d-4f transition of Ce3+, and other emission peaks with a dominated one at 575 nm corresponding to the 4F9/2-6H13/2 transition of Dy3+. The as-developed Sr2SiO4:Ce3+,Dy3+,Na+ phosphors exhibit excellent thermal stability. To be specific, the intensity retention rate of 425 and 572 nm at 300 °C is as high as 103.6 % and 89.2 %, respectively. Furthermore, near-ultraviolet (nUV) chip-pumped white LED prototypes were assembled using the co-activated phosphor and commercial green and red phosphors, which demonstrate its great potential in high-power white LEDs for solid-state lighting applications.

Functionalized cellulose nanocrystals-MoS2 nanosheets to tailor brick–mortar architecture of green composite for next-generation electronic packaging

Thermally conductive green composites are an attractive solution for addressing the escalating heat generation in miniaturized microelectronic devices. They offer simplicity in processing, cost-effectiveness, and the ability to potentially degrade, making them well-suited for overcoming heat-related challenges in next-generation electronics and 5G communication applications. Here, innovative work focuses on developing heat dissipation films by imitating artificial brick–mortar architecture. This approach incorporates cellulose nanocrystals-molybdenum disulfide (CNC-M) nanosheets as bifunctional fillers in polypropylene carbonate (PPC) via straightforward casting technology. This novel composite system leverages CNC-M nanosheets “brick” as oriented bonding and thermal linkers within the PPC “mortar,” significantly enhancing heat transfer across the film, enabling efficient heat propagation and overall thermal conductivity to 3.1 W·m−1·K−1, which is 4450.7 % higher than that of pure PPC. The superior heat dissipation capability enables these composite films to efficiently cool smartphone CPUs, shells, and high-power LED modules. When applying the composite film containing 8 wt% CNC-M to smartphone CPUs and cell phone shells, temperatures decrease by 17.9 °C and 8.3 °C, respectively. Notably, LED modules experience a significant temperature reduction of 22.6 °C. This distinctive “brick–mortar” architecture creates a homogeneous trapezoidal layered architecture that significantly enhances strong hydrogen bonding interactions within a composite film, resulting in exceptional mechanical properties, aging durability, and shape memory. The composite film with 5 wt% CNC-M exhibited impressive increases in tensile strength and Young’s modulus of 152.6 % and 1322.2 %, respectively. Furthermore, the composite film exhibited enhanced UV resistance and based materials. This study advances high-performance thermal conductive materials for electronics thermal management, paving the way for more efficient and sustainable solutions in electronics.

Nanostructured aramid fiber/Cu/BN composite Janus films with broadband electromagnetic interference shielding and superior thermally conductive/electrically insulating performance

Modern electronic technology necessitates the development of composite materials with effective electromagnetic protection. This work presents a novel strategy constructing an aramid nanofiber (ANF)-based Janus film (ANF@Cu-ANF/BN) using an electroless plating-vacuum assisted filtration-pressing technique. The film exhibits an unique asymmetric property profile, with one side being electrically conductive and thermally conductive/electrically insulating on the other. Exceptional EMI shielding effectiveness of 105.22 and 106.96 dB is obtained in the 8.2–12.4 GHz and 26.5–40 GHz ranges, respectively. In addition, the film demonstrates an impressive out-of-plane thermal conductivity of 2.703 W/(m·K). suggesting superior thermal management capabilities when integrated into heat sinks for high-power light-emitting diode modules. In terms of mechanical robustness, the film possesses a tensile strength of 14.31 MPa. The ANF@Cu-ANF/BN Janus composite films effectively harmonize electromagnetic shielding, thermal conductivity, and mechanical integrity, offering an innovative pathway of developing advanced materials that fulfill the stringent requirements of modern electronic devices.

Methods in molecular photocrystallography.

Over the last three decades, the technology that makes it possible to follow chemical processes in the solid state in real time has grown enormously. These studies have important implications for the design of new functional materials for applications in optoelectronics and sensors. Light-matter interactions are of particular importance, and photocrystallography has proved to be an important tool for studying these interactions. In this technique, the three-dimensional structures of light-activated molecules, in their excited states, are determined using single-crystal X-ray crystallography. With advances in the design of high-power lasers, pulsed LEDs and time-gated X-ray detectors, the increased availability of synchrotron facilities, and most recently, the development of XFELs, it is now possible to determine the structures of molecules with lifetimes ranging from minutes down to picoseconds, within a single crystal, using the photocrystallographic technique. This review discusses the procedures for conducting successful photocrystallographic studies and outlines the different methodologies that have been developed to study structures with specific lifetime ranges. The complexity of the methods required increases considerably as the lifetime of the excited state shortens. The discussion is supported by examples of successful photocrystallographic studies across a range of timescales and emphasises the importance of the use of complementary analytical techniques in order to understand the solid-state processes fully.

Heat Dissipation Enhancement of High-Power Deep-Ultraviolet LEDs Through Plated Copper on Thick Film Diamond Substrates

Heat Dissipation Enhancement of High-Power Deep-Ultraviolet LEDs Through Plated Copper on Thick Film Diamond Substrates

Self-Powered Intelligent Cooling System for High-Power Light-Emitting Diodes Based on Temperature Feedback Mechanism

Self-Powered Intelligent Cooling System for High-Power Light-Emitting Diodes Based on Temperature Feedback Mechanism

Utilizing a high power light-emitting diode to induce apoptosis of uterine carcinosarcoma (malignant mixed mullerian tumor) cells through a bi-phasic effect

Utilizing a high power light-emitting diode to induce apoptosis of uterine carcinosarcoma (malignant mixed mullerian tumor) cells through a bi-phasic effect

Development and numerical optimization of a cylindrical wire-fin-type integrated ionic wind heat sink for cooling high-power LEDs

Light-emitting diodes (LEDs) are becoming increasingly high-power and compact, which makes rotary fans incompetent in some cooling situations. The ionic wind technique can compensate for the shortcomings of rotating fans, owing to its benefits of no moving parts and compact structure. Integrating the ionic wind generator with heat dissipation fins can effectively reduce the size of LED devices, but research in this area is still insufficient. In this study, an integrated ionic wind heat sink is designed for cooling LEDs. The multi-physical characteristics of discharge, flow, and heat transfer are numerically studied. The geometric parameters’ impact degree and mechanism on the multi-physical characteristics are analyzed. The performance optimization of the integrated heat sink is realized and verified. The fin length, flow channel center angle, and relative position of the fin have a large influence on the average velocity of ionic wind. The relative position of the wire electrode determines the electric field strength distribution, and it has the greatest influence on the ionic wind performance. The emitting electrode being placed at the inlet edge of the collecting electrode produces a high ionic wind flow rate. The integrated ionic wind heat sink designed in this study exhibits an outstanding cooling performance and temperature uniformity. This device can cool down the surface of a heat source with a power of 200 W to below 91 °C and make the average heat transfer coefficient reach 18.6 W/(m2·K). This study proposes a valuable method to optimize the integrated ionic wind heat sink for cooling high-power electronic devices.

Effect of time and photoactivated face on bond strength of brackets and on degree of monomer conversion.

To evaluate the effect of four different photoactivation protocols (according to "photoactivated faces" - mesial/distal, cervical/incisal or center - and "photoactivation time" - 6-3s) of a high-power photo activator (Valo Cordless®-Ultradent) on the shear bond strength (SBS) between metal brackets and dental enamel and on the degree of conversion (DC) of an orthodontic resin. 40 bovine incisor crowns were randomly assigned to 4 groups (n = 10). The brackets were bonded with Transbond XT® resin using 4 protocols according to the "photoactivation protocol" factor (which was subdivided into photoactivated faces and photoactivation time): V3C = 3s + center; V6C = 6s + center; V3M3D = 3s on mesial + 3s on distal; V3C3I = 3s on cervical + 3s on incisal. All the samples were stored for 4 months (water,37ºC) and then subjected to a SBS test (100KgF,1mm/min). 40 resin discs were made to evaluate the monomer degree of conversion. Data from the SBS and DC were assessed by One-way ANOVA and Tukey's test (5%). Bond failures were analyzed according to the Adhesive Remnant Index (ARI) and evaluated by the Kruskal-Wallis test (5%). There was a statistically significant difference (p = 0.008) in the One-way ANOVA result for SBS values between all groups, but the protocols showed statistically similar results (p ≥ 0.05-Tukey's tests) concerning the photoactivated faces (V6C, V3M3D and V3C3I) and photoactivation time (V3C and V6C) factors individually. There was no statistically significant difference (p ≥ 0.05) in the One-way ANOVA result for DC values. The SBS and DC values will vary depending on the protocol applied. It is possible to maintain the bracket fixation quality with the use of a high-power LED photo activator associated with a shorter photoactivation time. However, it is assumed that not all types of protocols that might be applied will provide quality bonding, such as V3C, V3M3D and V3C3I, which may - depending on the SBS and DC values - affect the final treatment time, due to brackets debonding, or increase of possibility of damage to dental enamel during bracket removal. Clinical studies are suggested to confirm the hypotheses of this research.

Near-infrared-emitting (Gd1-yNdy)3(Ga1-xCrx)5O12 Glass Ceramic Phosphors for Light-emitting Diodes

In this study, we proposed a blue-excitable and near-infrared (NIR) emission ceramic phosphor - Gd3Ga5O12:Cr3+, Nd3+ (GGO:Cr, Nd) by a solid-state reaction for light-emitting diode applications. The as-synthesized Gd3Ga4.95Cr0.05O12 phosphor displayed a broad emission peak at 759 nm (4T2 → 4A2) with a full-width-half-maximum of 122 nm under 460 nm excitation. In order to generate NIR, we introduced Nd3+ ions as activators to substitute Gd3+ ions in GGO:Cr3+ phosphors. Via energy transfer from Cr3+ ions to Nd3+ ions in GGO, an intense NIR emission at 1064 nm resulting from 4F3/2 → 4I11/2 is demonstrated. Furthermore, we investigate the doping effects at various concentrations and reanalyzed the luminescent characteristics of (Gd1-yNdy)3(Ga1-xCrx)5O12 phosphors to determine the optimal doping concentration of Cr and Ni, which were found to be 1 mol.% and 3 mol.%, respectively. Finally, we mix the composition-optimized (Gd0.97Nd0.03)3(Ga0.99Cr0.01)5O12 NIR-emission phosphor with silica-based glass powder. After cold pressing and high-temperature sintering using molds, we obtain NIR-emitting glass-ceramic phosphors through laser cutting technology and packaged them into high-power light-emitting diodes.

Phosphor-in-glass film sintered on sapphire lens for laser welding hermetic packaging of high-power white LEDs

White light-emitting diodes (WLEDs) represent a revolutionary type of energy-saving and environmentally friendly light source, which has been extensively employed in a multitude of lighting and display applications. Nevertheless, traditional organic packaging is unable to fulfill the requirements of highly reliable high-power WLEDs, including hemertic property, heat resistance, and excellent luminous properties. Herein, an all-inorganic hermetic packaging based on laser-localized welding and phosphor-in-glass film sintered on a sapphire lens (PiGF-SL) has been developed for high-power WLEDs. The PiGF-SL with a Kovar frame was welded to a three-dimensional direct-plated ceramic (3D-DPC). The high-strength and crack-free welded joint with a shear strength of 258.83 MPa and packaging cavity with excellent gas tightness (leakage rate 8.6 × 10−10 Pa m3/s) were simultaneously obtained, resulting in the high-power WLED capable of maintaining its excellent optical properties for an extended period in harsh environments. Furthermore, the optical performance of welded WLEDs was optimized by adjusting the PiGF-SL film thickness and red CaAlSiN3:Eu2+ (CASN) phosphor content. The welded WLED emits a cool white light by improving the PiGF thickness to 91 μm and exhibits high color quality with red CASN phosphor content of 8 wt%, which simultaneously presents outstanding color rendering index (CRI) of 91, luminous efficacy (LE) of 44.8 lm/W, and correlated color temperature (CCT) of 4322 K. Following a 200-h aging process, the laser-welded PiGF-SL-based WLED exhibited a slightly reduced efficiency loss and a stable color quality in comparison to reflow-soldered and epoxy-bonded WLEDs. Our work provides valuable guidance and solutions for the highly reliable and board-level packaging of WLEDs.

Hybrid six sigma based on recursive kalman filter and weibull distribution to estimate the lifespan of Bulb LEDs

The durability of LED bulbs ensures that the lights can operate for a long time without needing to be replaced or maintained too often. The brightness of high-power LED bulbs provides a strong and efficient light source, saves energy, and has a long lifespan. The traditional method of testing LED bulb life span has limitations such as long testing time, limited accuracy, high cost, inability to predict accurately, and failure to respond quickly. Therefore, the development of new and improved testing methods is necessary to effectively and accurately evaluate and ensure the durability of LED bulbs. This research paper proposes a hybrid Six Sigma method based on the recursive Kalman filter and Weibull distribution to estimate the lifespan of Bulb LEDs. The goal of the new method for evaluating LED bulb life is to provide accurate, reliable, and multi-dimensional information about the life of LED lamps, meeting the requirements of accuracy, diversity, time-saving, resources, credibility, and the ability to evaluate from a variety of perspectives. As a result of the research, the recursive Kalman filter method has strengths such as high accuracy, flexibility, saving computational resources, the ability to handle inaccurate data, and scalability. When applied to LED bulb life assessment, it provides an accurate and reliable estimate of LED lamp life. Research results on longevity testing were reduced from 1650 h to 710 h. The end-of-life test time is 710 h, and the aging time per life test cycle is 135 h. The cost of life testing is reduced from 2100.17 USD to 410.12 USD. This LED bulb lifespan testing method can be applied to similar types of LED products to improve the company's productivity and business efficiency.

Five-Surface Phosphor-in-Glass for Enhanced Illumination and Superior Color Uniformity in Large-View Scale LEDs.

A novel five-surface phosphor-in-glass (FS-PiG) structure for high illumination and excellent color uniformity in large-view scale LEDs for sensor light source application is demonstrated. YAG phosphor (Y3Al5O12:Ce3+) was uniformly mixed with ceramic and sintered at 680 °C to form a phosphor wafer. Sophisticated laser engraving was employed on the phosphor wafer to form saddle-shaped large-view scale FS-PiG LEDs. The performance of the FS-PiG LEDs exhibited an illumination of 401 lm, average color temperature (CCT) of 5488 K ± 110 K, and color coordinates (CIE) of (0.3179 ± 0.003, 0.3352 ± 0.003). In contrast to convention single-surface phosphor-in-glass (SS-PiG) LEDs, the performance exhibited an illumination of 380 lm, average CCT of 5830 K ± 758 K, and CIE of (0.3083 ± 0.07, 0.3172 ± 0.07). These indicated that the performance of the FS-PiG LEDs was higher than the SS-PiG LEDs for illumination, CCT, and CIE by 1.7, 7, and 23 times, respectively. Furthermore, the FS-PiG LEDs demonstrate a lower lumen loss of 2% and a reduced chromaticity shift of 5.4 × 10-3 under accelerated aging at 350 °C for 1008 h, owing to the high ceramic melting temperature of up to 510 °C. In this study, the proposed FS-PiG large-view scale LEDs with excellent optical performance and high reliability may be promising candidates to replace the conventional phosphor-in-organic silicone material used in high-power LEDs for the next generation of sensor light sources, display, and headlight applications.

Highly effective red phosphor for warm white LEDs without rare earth elements

The use of red fluorescent powder derived from nitrides and oxides in warm white LEDs is a pressing concern due to its lower quantum efficiency. Fluoride red phosphors activated by Mn4+ ions show promising potential for application in white light-emitting diodes (LEDs) due to their distinctive narrowband red emission and broad blue excitation, along with the relatively mild synthesis conditions required. However, the quantum efficiency of early Mn4+-doped fluoride phosphors was not optimal, highlighting the importance of identifying a suitable preparation method and matrix. Here, we introduce an efficient and thermally stable red fluoride phosphor, Cs2SiF6:Mn4+, which demonstrates a remarkable quantum efficiency of 98.32 % achieved through ion exchange techniques. However, even at a temperature of 423 K, the luminous intensity still maintained at 95 % of that under room temperature conditions. By incorporating Cs2SiF6:Mn4+ as a red emitter, a stable 10 W high-power warm white LEDs with a luminous efficiency of approximately 126.1 lm/W can be realized. These findings underscore the significant potential of the red phosphor Cs2SiF6:Mn4+ in advancing high-performance, high-power warm white LEDs.

Near-infrared optical properties of Cs2KScF6:Cr3+ phosphor for high-power light-emitting diodes

The recent years have witnessed a great leap for near-infrared (NIR) spectroscopy technology in multifunctional application fields. In this study, a double-perovskite structured Cr3+-doped Cs2KScF6 fluoride NIR phosphor with peak location at 778 nm and full-width at half maximum (FWHM) of 95 nm was synthesized by a co-precipitation method. The integral emission intensity at 423 K retains 70 % of that at room temperature (RT), showing good luminescent thermal stability. Combining the obtained phosphor in an NIR phosphor converted light-emitting diode (NIR pc-LED) device, the output power and photoelectric conversion efficiency can reach 72.28 mW and 6.83 % at 320 mA. By virtue of the good optical performance, clear structural images of different fruits were visualized by using the NIR pc-LED as light source, suggesting the potential of Cs2KScF6:Cr3+ phosphor to be used in high-power LED devices.