High Power LED Research Articles

Desarrollo de un sistema electrónico con desplazamiento bidimensional para obtener el flujo lumínico en distintas fuentes de iluminación para conseguir sus curvas características

A control electronic system was developed with equidistant perpendicular displacements to obtain the light intensity of different lighting sources, with a data acquisition card to graph the characteristic curves in an obscure chamber. An aluminum structure was implemented, placing bands jagged on each axis and mounted on the gear of each of the with bipolar steps motors, which allow movement in two-dimensional form. A graphical interface was generated to control the resolution of the displacement and 3D supports were designed to place the light flow sensor, obtaining the characteristic curve of the different types of lighting sources as LED panel, Compact Fluorescent Lights, high power LED, and incandescent in the experimental arrangement. This type of system presents diverse benefits for applications in the characterization of lenses, lasers or optical sensors to apply them in the field of electronics, mechatronics and robotics. The system allows to obtain the curve of light intensity that can determine the behavior of the light source in accordance with the two-dimensional displacement of equidistant form shown in a graphical interface.

Thermal Issues of Warm and Cool White LED Bulbs

For modern high-power LEDs, self-heating becomes a critical factor determining their functional characteristics and lifetime. For large-area LEDs with a complex structure, it is important to know not only the thermal resistance but also the detailed temperature distribution (temperature map) over the active area. In this paper, we present the thermal analysis of high-power Light-Emitting Diodes (LEDs) with under the real operating conditions. Thermal transient measurements were performed to study the thermal characteristics of high power LED bulbs. The purpose of this test is to analyze the heat dissipation from LED Lamps. The study concludes that the warm white LED bulbs show better thermal behavior than the cool white LED bulbs of low power.

Crystal structure insight aided design of SrGa2Si2O8:Mn2+ with multi-band and thermally stable emission for high-power LED applications

Mn2+ ion is commonly used as a luminescent center of phosphors for long-wave emission, however, it is difficult to achieve Mn2+-activated phosphors with both broadband emission and high thermal stability, which limits their application in the field of high-power phosphor-converted white light-emitting diodes (PC-wLEDs). In this work, from the viewpoint of crystal structure, we develop a novel Mn2+-doped phosphor, SrGa2Si2O8:Mn2+, to realize multi-band and thermal-stable emission. We found that the multiple band emission originates from three Mn2+-induced luminescence centers, i.e. Mn2+ in Ga3+ site, Mn2+ in Sr2+ site, and Mn2+-Mn2+ dimers, due to their different crystal field environments. Meanwhile, excellent thermal-stable emission (up to 200 °C) is obtained as a result of the energy transfer between the traps and the luminescence centers. What is more, the different energy transfer paths of the SrGa2Si2O8:Mn2+ lead to a red-shift of emission, which can help to improve color rendering index of light sources. Our results demonstrate that this new phosphor shows a potential for the application of high-power PC-wLEDs.

Qualitative analysis of coupling effect of fluid velocity distribution in microchannels on the performance of the LED water cooling system

PurposeThe purpose of this paper is to ensure adequate thermal management to remove and dissipate the heat produced by a light-emitting diode (LED) and to guarantee reliable and safe operation.Design/methodology/approachA three-dimensional (3-D) computational fluid dynamics (CFD) model was used to analyze the distribution of fluid velocities among microchannels at four different aspect ratios.FindingsThe results showed that at the same inlet flow rate, the larger the aspect ratio of the microchannels, the better the uniformity of the internal fluid velocity and thus better the heat dissipation performance on the surface of the high-power LED chip. In addition, the thermal performance of a high-power LED water cooling system with four different aspect ratios’ microchannel structures is further studied experimentally. Specifically, the coupling effect between the fluid velocity distribution in the microchannels and the heat dissipation performance of a high-power LED water cooling system is qualitatively analyzed and compared with the simulation results of the fluid velocity distribution. The results fully demonstrated that a larger aspect ratio of the microchannels results in better heat dissipation performance on the surface of the high-power LED chip.Originality/valueOptimizing the structural parameters to facilitate a relatively uniform velocity distribution to improve the water cooling system performance may be a key factor to be considered.

Fast sintering method of phosphor-in-glass for high-power LEDs

Fast sintering of Phosphor-in-Glass (PiG) by means of CO2 laser heating has been successfully achieved. PiGs samples fabricated at different exposure times were characterized and compared with a PiG sample synthetized through an electric furnace. An exposure time as short as 30 s and 12 W of optical power is necessary to sintering PiGs. Results show that the optimization of CO2 laser approach can dramatically reduce up to 60 times the PiGs sintering. Luminous Efficacy (LE) of at least 79.7 lm/W as well as minimum Color Rendering Index (CRI) value of 70 for all fabricated PiGs were obtained. Correlated Color Temperature (CCT) value decreased gradually as the CO2 laser exposure time increased. These results show that PiGs samples, synthetized with short exposure times, show excellent lighting properties.

Enhanced Heat Dissipation of High-Power Light-Emitting Diodes by Cu Nanoparticle Paste

Light-emitting diodes (LEDs) are considered as a next-generation lighting due to their high luminous efficiency, low power consumption, and long lifetime. However, the low heat dissipation of LEDs is an inevitable roadblock. Here, a high heat-conducting Cu nanoparticle (NP) paste was prepared and demonstrated for high-power LEDs. The effects of sintering temperature on the electrical and thermal properties of the Cu NP paste were investigated. The junction temperature change and thermal resistance of LEDs were measured and compared with the traditional die-attach materials. Consequently, the Cu NP paste sintered at 250 °C possesses low electrical resistivity of $5.1~{ \mu \Omega \cdot }$ cm and high thermal conductivity of 142.37 W/(m.K). The packaged LEDs display the low thermal resistance of 6.58 K/W and the low junction temperature change of 3.22 °C, which are significantly lower than those of LEDs packaged by the traditional die-attach materials. These results demonstrate that the promising Cu NP paste provides a feasible and effective strategy for enhancing the heat dissipation of high-power LEDs.

Thermostability and reliability properties studies of transparent Ce:GdYAG ceramic by Gd substitution for white LEDs

Yttrium Aluminum Garnet transparent ceramics with different Gd3+ concentrations ((Ce0.001GdxY0.999-x)3Al5O12) ceramics were prepared by the conventional solid state reaction technology and vacuum sintering method, and the ceramic-based LEDs with blue LED were prepared by flip chips and Chip on board package. The extreme circumstance of −40 °C and 150 °C alternate environments, high humidity and high temperature as well as xenon lamp aging test for a long time are mentioned to explore the reliability of phosphor ceramics, respectively. And the thermostability and the effect of Gd3+ doping on the PL properties of ceramics were also investigated. What is more, the effects on the optical performance of the ceramic-based LEDs have been also investigated. As Gd3+ concentration added from 0 to 0.5, the PL spectra peaks of phosphor shifted from 542 nm to 575 nm under the excitation of 460 nm. It can be summarized that the increase of Gd3+ concentration could not improve the thermostability, but enhance the reliability when the x value is x is not greater than 0.4. What is more, the ceramics-based LED of x = 0.3 instead of x = 0.4 has the best reliability after the xenon lamp aging and thermal cycling test. And the ceramics-based LED of x = 0.45 has the best reliability after the high humidity and high temperature test. Compared with Ce:YAG and Ce:LuAG ceramics, although the increase of Gd3+ concentration decreases the thermostability and luminous efficiency, the Gd substitution can enhance the reliability and solve the lack of red light in the spectrum of Ce:YAG and Ce:LuAG ceramics, which has improved the performance of Ce:GdYAG ceramics for high-power warm white LEDs.

Transparent Ceramics Enabling High Luminous Flux and Efficacy for the Next-Generation High-Power LED Light.

By designing novel chemical compositions and controlling precursor powders, perfect transparent ceramics (TCs) of Gd3Al4GaO12:2%Ce3+ garnets (GAGG:2%Ce3+) were achieved for the first time. Ce3+ distributions in ceramics were revealed by micromorphology and micro-cathodoluminescence. Benefiting from the components that are rich in red emission, warm light with a correlated color temperature of about 2800 K was generated when TC was used in high-power (hp) blue light emitting diodes (LEDs) (∼450 nm, ∼34 W driven at 1 A). The hp LED device shows high brightness with a luminous flux nearly 2100 lm. The luminous efficacy even reaches 388 lm/W, which is the highest value reported till now, indicating that the use of GAGG:2%Ce3+ TCs promises energy saving. We believe that this work will open a new perspective to develop TCs for next-generation hp LED lighting to substitute traditional hp xenon lamps and high-pressure sodium lamps.

Thermally stable lead-free phosphor in glass enhancement performance of light emitting diodes application.

A co-sintering method for preparing PIG is proposed, a Ce3+ doped yttrium aluminum garnet (YAG:Ce) phosphor in glass (PIG) slice is fabricated through co-sintering polycrystalline Ce:YAG phosphor, and a new, to the best of our knowledge, homemade matrix glass SiO2-K2O-BaO-B2O3 glass powder is detected to confirm crystal phase by X-ray powder diffractions (XRD) and micromorphology by scanning electron microscope (SEM). The YAG:Ce phosphor particles dispersed in the matrix are vividly observed and their distributions are relatively uniform. The PIG packaged light-emitting diode (LED) sample shows a relatively lower correlated color temperature (CCT) than the conventional phosphor-dispensing LED sample. White light can be achieved in the PIG slice under 465nm LED excitation by controlling the phosphor concentration or thickness. The highest luminous efficacy of the PIG slice packaged white LED is 94.67lm/W at 100mA. Controllable geometrical and optical properties of the YAG:Ce PIG can generate evident improvements in the manufacturing of identical CCTs for high-power white LEDs. The combination of PIG with a blue LED chip of a specific wavelength, if measured before final assembly, enables targeted production of specific CCT white LEDs. PIG technology allows the realization of high stability and thermal conductivity for the phosphor layer. This simple method provides many possibilities for LED packaging, including thin film flip chip and remote phosphor technology.

Towards real-time multispectral endoscopic imaging for cardiac lesion quality assessment.

Atrial fibrillation (Afib) can lead to life threatening conditions such as heart failure and stroke. During Afib treatment, clinicians aim to repress unusual electrical activity by electrically isolating the pulmonary veins (PV) from the left atrium (LA) using radiofrequency ablation. However, current clinical tools are limited in reliably assessing transmurality of the ablation lesions and detecting the presence of gaps within ablation lines, which can warrant repeat procedures. In this study, we developed an endoscopic multispectral reflectance imaging (eMSI) system for enhanced discrimination of tissue treatment at the PV junction. The system enables direct visualization of cardiac lesions through an endoscope at acquisition rates up to 25 Hz. Five narrowband, high-power LEDs were used to illuminate the sample (450, 530, 625, 810 and 940nm) and combinatory parameters were calculated based on their relative reflectance. A stitching algorithm was employed to generate large field-of-view, multispectral mosaics of the ablated PV junction from individual eMSI images. A total of 79 lesions from 15 swine hearts were imaged, ex vivo. Statistical analysis of the acquired five spectral data sets and ratiometric maps revealed significant differences between transmural lesions, non-transmural lesions around the venoatrial junctions, unablated posterior wall of left atrium tissue, and pulmonary vein (p < 0.0001). A pixel-based quadratic discriminant analysis classifier was applied to distinguish four tissue types: PV, untreated LA, non-transmural and transmural lesions. We demonstrate tissue type classification accuracies of 80.2% and 92.1% for non-transmural and transmural lesions, and 95.0% and 92.8% for PV and untreated LA sites, respectively. These findings showcase the potential of eMSI for lesion validation and may help to improve AFib treatment efficacy.

Realization of high-power dimmable GaN-based LEDs by hybrid integration with AlGaN/GaN HFETs

We successfully demonstrated high-power dimmable GaN-based vertical injection LEDs (VI-LEDs) by integration with AlGaN/GaN-based heterojunction field-effect transistors (HFETs) using a flip-chip bonding technique. The high-power dimmable GaN-based VI-LEDs on AlGaN/GaN HFETs emitted no light in the off-state of the HFETs and operated normally in the on-state of the HFETs. Furthermore, the light-output power (LOP), forward current, and maximum electroluminescence (EL) intensity were efficiently modulated with the gate-to-source voltage (VGS) of the HFETs. The temperature rose by less than 20 °C when the devices were operated with a VGS of −3 V and supply voltage (VDD) of 10 V. These results suggest that the high-power dimmable GaN-based VI-LEDs can be fabricated through hybrid integration with AlGaN/GaN HFETs, and the devices could be applied to novel applications such as visible light communication (VLC) and adaptive headlights for vehicles.

Cost-Effective Copper⁻Nickel-Based Triboelectric Nanogenerator for Corrosion-Resistant and High-Output Self-Powered Wearable Electronic Systems.

Recent years, triboelectric nanogenerators (TENGs) have attracted increased attention from researchers worldwide. Owing to their conductivity and triboelectric characteristics, metal materials can be made as both triboelectric materials and conductive electrodes. However, the surface of typical metals (such as copper, aluminum, and iron) is likely to be corroded when the sweat generated by human-body movement drops on the surface of TENGs, as this corrosion is detrimental to the output performance of TENGs. In this work, we proposed a novel corrosion-resistant copper–nickel based TENG (CN-TENG). Copper–nickel alloy conductive tape and polytetrafluoroethylene (PTFE) tape played the role of the triboelectric materials, and polymethyl methacrylate (PMMA) was utilized as the supporting part. The conductive copper–nickel alloy tape also served as a conductive electrode. The open-circuit voltage (VOC) and short-circuit current (ISC) can arrive at 196.8 V and 6 μA, respectively. Furthermore, peak power density values of 45 μW/cm2 were realized for the CN-TENG. A series of experiments confirmed its corrosion-resistant property. The approximate value of VOC for the fabricated TENG integrated into the shoe reached 1500 V, which is capable of driving at least 172 high-power LEDs in series. The results of this research provide a workable method for supporting corrosion-resistant self-powered wearable electronics.

Comparative Analysis Between Water-Cooled and Air-Cooled Heat Dissipation in a High-Power Light-Emitting Diode Chipset

With a substantial increase in thermal power density, the operating temperature of high-power light-emitting diodes (LEDs) rises rapidly, exerting a notable effect on chipsets’ performance. A water-cooled microchannel radiator and an air-cooled radiator are proposed to solve this problem. The effects of key factors of both radiators on heat dissipation in a high-power LED chipsets, and general comparisons between each method, are analyzed via Fluent. The simulation results indicate that heat dissipation from the water-cooled microchannel radiator is readily affected by the microchannel’s flow rate and aspect ratio. A larger flow rate and larger aspect ratio favor improved heat dissipation in the water-cooled microchannel radiator. Heat dissipation in the air-cooled radiator is related to volumetric flow rate, rib number, rib height, rib thickness, and substrate thickness. A larger volumetric flow rate, rib number, and rib height favor heat dissipation in the air-cooled radiator. However, there is a critical thickness value: if the thickness is less than the critical value, heat dissipation is greatly affected by rib thickness and substrate thickness, if the thickness is larger than the critical value, the influence is insignificant. The high-power LED chipsets’ temperature is also related to the insulating substrate’ input power and thermal conductivity. A large input power leads to a substantial increase in temperature, and larger thermal conductivity of the insulating substrate minimizes temperature increase in the high-power LED chipsets. When comparing the two radiators, results show an air-cooled radiator should be used in low-power LED chipsets. When an air-cooled radiator cannot satisfy the chipset’s needs, a water-cooled microchannel radiator should be utilized.

Development of cryostat integrated TL/OSL reader for its application in radiation dosimetry

Abstract A cryostat based integrated TL/OSL reader has been designed and developed to study the temperature dependence of photoionization cross-section at various low temperatures. The system has the facility to record thermoluminescence (TL) as well as optically stimulated luminescence (OSL) at various low temperatures from −150 to 250 ∘ C. It facilitates the measurement of OSL at various temperatures thus; temperature dependence of OSL at various low temperatures can be studied. A PID (Proportional–Integral–Derivative) based temperature controller has been designed and incorporated for generating and controlling user defined heating profiles for the TL measurements in the reader system. The reader system can measure the temperature of the planchet within ± 1 ∘ C precision. The optical stimulation unit consists of two high power LEDs fitted in two channels and optically focused on the sample. In the OSL operation, besides the conventional CW-OSL, LM-OSL modes a non-linear OSL (NL-OSL) method has been incorporated in the reader system. The sensitivity of the system is found to be comparable to that of commercial Riso reader system in OSL mode. The OSL grade α -Al2O3:C phosphor was used to test the reader system and investigate the temperature dependence of OSL in this phosphor at low temperature regime. We report the results of OSL experiments on α -Al2O3:C, and of generalized numerical simulations of potential OSL behaviour with temperature. The photoionization cross-section of shallow as well as dosimetric traps has been evaluated numerically as well as experimentally. The design concept of the reader system and the results of low temperature OSL are discussed.

Highly efficient GaN-based high-power flip-chip light-emitting diodes

High-power flip-chip light-emitting diodes (FCLEDs) suffer from low efficiencies because of poor p-type reflective ohmic contact and severe current crowding. Here, we show that it is possible to improve both the light extraction efficiency (LEE) and current spreading of an FCLED by incorporating a highly reflective metallic reflector made from silver (Ag). The reflector, which consists of an Ag film covered by three pairs of TiW/Pt multilayers, demonstrates high reflectance of 95.0% at 460 nm at arbitrary angles of incidence. Our numerical simulation and experimental results reveal that the FCLED with Ag-based reflector exhibits higher LEE and better current spreading than the FCLED with indium-tin oxide (ITO)/distributed Bragg reflector (DBR). As a result, the external quantum efficiency (EQE) of FCLED with Ag-based reflector was 6.0% higher than that of FCLED with ITO/DBR at 750 mA injection current. Our work also suggests that the EQE of FCLED with the Ag-based reflector could be further enhanced 5.2% by replacing the finger-like n-electrodes with three-dimensional (3D) vias n-electrodes, which spread the injection current uniformly over the entire light-emitting active region. This study paves the way towards higher-performance LED technology.

(Invited) A Review on the Role of Slurry Chemistry on Chemically Modified Thin Film Formation for CMP Applications

Chemical Mechanical Planarization (CMP) process is currently facing the challenge of planarizing larger scale wafers at an atomic scale precision with superior removal rate selectivity and zero defect focus. While the horizontal dimensions of the processed wafers (x-axis and y-axis as the wafer diameter) extend up to 300 mm, the z-axis has to be planarized to a margin of a couple of hundred nanometers. This requirement highlights the need for fundamental understanding on the surface chemistry of the layers being exposed to the planarization process in terms of their interactions with the CMP slurry chemistry. Once the behavior of the wafer surface is understood at an atomic level, the process control metrics can be tuned accordingly. This paper reviews the role of slurry chemistry in effectively modifying the top surface films of the various materials including conductors, semiconductors and insulators exposed to CMP operations in semiconductor manufacturing. Metallic films are studied in terms of their corrosion and passivation behavior [1, 2] as well as through a modeling of the energy minimization through a Cahn Hilliard Equation (CHE) approach [3]. Furthermore, formation and selectivity properties of the semiconductor materials including conventional and III-V semiconductors and insulators were investigated [4-5]. Some high-end applications where the nano-scale chemically modified films critical are: Metal CMP applications of the tungsten T-gate transistors, new barrier materials, germanium based high-speed shallow trench isolation transistors and high-power transistors and LED applications where III/V semiconductors, such as GaN, are used. Ozdemir, Basim, G.B. “Effect of Chemical Mechanical Polishing on Surface Nature of Titanium Implants FT-IR and Wettability Data of Titanium Implants Surface After Chemical Mechanical Polishing Implementation”, Data in Brief, 10, P 20-25, 2017. Karagoz, A., and Basim, G.B. “Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents”, ECS Journal of Solid State Science and Technology, CMP Special Issue, 4 (11) P5097-P5104, 2015. Karagoz, A., Sengul, , Basim, G.B., “A Cahn Hilliard Modeling of Metal Oxide Thin Films for Advanced CMP Applications”, 225th ECS Meeting – Orlando, Florida, USA, May 11-15, 2014, ECS Transactions, 61 (17) 15-20 (2014). Karagoz, A., Craciun, V., Basim, G.B., “Characterization of Nano-Scale Protective Oxide Films_ Application on Metal Chemical Mechanical Planarization”. ECS Journal of Solid State Science and Technology, 4 (2) P1-P8, 2015. Ozbek, S., Akbar, W., Basim, G.B. “ Optimized Process Design for GaN Chemical Mechanical Planarization” ECS Journal of Solid State Science and Technology, Special Issue on GaN-Based Electronics for Power, RF, and Rad-Hard Applications, 6-11, P S3084-S3092, 2017.

Efficient and heat-conducting color converter of phosphor glass film printed on sapphire substrate for high-power white LEDs/LDs

Thermal stability and heat dissipation of color converter are the key roadblocks for high-power white light-emitting diodes (LEDs) and laser diodes (LDs). In this work, we fabricated an efficient and heat-conducting color converter based on phosphor-sapphire composite (PSC) for white LEDs/LDs, in which Y3Al5O12:Ce3+ or Y3Al5O12:Ce3+/CaAlSiN3:Eu2+ phosphor glass film was sintered on a sapphire substrate by using low-melting borosilicate glass. The Y3Al5O12:Ce3+ PSC-based white LEDs achieve a high luminous efficacy of 155 lm/W, and the Y3Al5O12:Ce3+/CaAlSiN3:Eu2+ PSC-based white LEDs exhibit a warm white light with a correlated color temperature of 3509 K and a color rendering index of 88.3. The chromaticity of PSC-based white LDs shifts from cool to warm white. Furthermore, the PSC achieves a high thermal conductivity of 20.8 W m−1 K−1, which provides the effective heat transfer channels. The working temperature of PSC is reduced by 46 °C compared with that of phosphor-in‑silicone.

Synthesis and characterization of aminolevulinic acid with gold and iron nanoparticles by photoreduction method for non-communicable diseases diagnosis and therapy

Non-communicable diseases (NCDs) are a group of chronic diseases resulted by genetic, epigenetic and environmental factors and life style. The main types of NCDs are cardiovascular diseases and cancers. Some of therapeutic treatments for NCDs induce severe cytotoxicity to normal cells. New treatments as photodynamic and sonodynamic therapies have been proposed trying to improve the cure rate and reduce the side-effects. In these treatments certain drugs as porphyrins precursors associated to metal nanoparticles (MNPs) have become of extreme interest since have high targeting ability and potentiality to destroy tumor tissues. MNPs can induce cell death through various processes, including reactive oxygen species (ROS) generation and DNA damage, among others. In this work, we describe synthesis of MNPs by photoreduction with aminolevulinic acid (ALA), a protoporphyrin IX precursor. To obtain ALA:MNPs (M = Au or/and Fe), ALA, polyethylene glycol, and Tetrachloroauric acid and/or iron powder water solutions were irradiated by Xenon lamp. The UV–vis spectra, transmission electron microscopy and zeta potential were measured to characterize nanoparticles. The proposed mechanism of nanoparticle formation was described from a physicochemical perspective. The THP-1 macrophages cytotoxicity was determined, and photodynamic therapy (PDT) with high power LED at 590 nm for 2 min were performed. The results have suggested that the gold/iron nanoparticles interfere in the selectivity of iron transport across the mitochondrial inner membrane and enhance the effectiveness of the PDT acting as important agent for NCDs control.

Development of β-SiAlON:Eu2+ phosphor in glass for high-power LED- and LD-based lighting systems using original BaO-B2O3-ZnO-SiO2 (BBZS) composition glass

Green-emitting phosphor-in-glass (PiG) materials with a high luminescence efficiency and high color rendering index were developed by co-firing commercial β-SiAlON:Eu2+ phosphor powder and BaO-B2O3-ZnO-SiO2 (BBZS) glass frits possessing a low glass transition temperature (Tg = 560 °C). In agreement with the photoluminescence spectral profiles of powder materials, β-SiAlON:Eu2+ PiG materials showed a broad excitation band from 220 to 500 nm and a narrow emission band at 530 nm under excitation at 450 nm. The β-SiAlON:Eu2+-based PiG exhibited excellent heat resistance, with its relative emission intensity at 200 °C being 83% that at 30 °C. On varying the β-SiAlON:Eu2+ phosphor content in the PiG-based light emitting diodes (LEDs), the highest luminous efficacy was obtained for the 10 wt% β-SiAlON:Eu2+ phosphor-doped PiG sample, and the internal quantum efficiency of this sample under excitation at 450 nm was 56%. By combining the PiG materials prepared in this study with a blue chip-on-board (incident power = 100 mA), the 10 wt% β-SiAlON:Eu2+-based PiG chip module showed a luminous efficacy of 80 lm/Wrad. The PiG-based LED maintained its high luminous efficacy when incident power on the blue chip-on-board increased up to 4 W (220 lm/Wrad). Under blue laser excitation (incident power = 1500 mA), the β-SiAlON:Eu2+-based PiG materials showed a linear relationship between luminous flux and incident laser power. With increasing incident laser power, the luminous flux effectively increased, and the 10 wt% β-SiAlON:Eu2+-based PiG sample showed a luminous efficacy of 300 lm at an incident laser power of 1500 mA.

Tunable blue/yellow emission in high-power white LED devices packaged with Ce:(Y, Gd)AG transparent ceramics

Abstract White LEDs have been widely used in various lighting applications. However, applying them to high lumen density systems remains a challenging issue due to the aging of the organic packing materials. In this paper, Ce:(Y, Gd)AG transparent ceramics with different Gd3+ substitution concentrations were fabricated via solid-state reaction method under different sintering temperatures and used to construct high-power white LED devices to evaluate their optical, luminescence, and thermal properties. The energy band structure of Ce3+ was effectively tailored by the energy level compressing and orbital hybridisation effects, resulting in the tunability of the blue/yellow emission of the devices and the luminescence redshift of Ce:(Y, Gd)AG ceramics. The transmittance of Ce:(Y, Gd)AG transparent ceramics had almost no impact on the photoluminescence spectra yet exhibited strong dependence on the Gd3+ substitution concentration. The emitted light of LED devices packaged with the ceramics changed from blue-white to yellow-white while increasing Gd3+ concentrations from 0.0 to 30.0 at.%. The as-assembled white LED devices exhibited excellent heat dissipation performance, uniform intensity distribution, and strong intensity in the forward direction. The industrialisation of Ce:YAG transparent ceramics-based LED devices can be accelerated especially in high-power lighting.