Phosphor Conversion Research Articles

Blue-green emitting LuASG:Ce phosphor ceramics with high luminous efficacy for high-power LEDs

Phosphor-converted blue-green emitting high-power LEDs (hp-LEDs) are essential for marine fishery and ocean optical communication. Here the blue-green emitting Sc3+-doped LuAG:Ce (LuASG:Ce) phosphor ceramics (PCs), as the phosphor converter of high-power LEDs (hp-LEDs), were successfully prepared by vacuum solid-state sintering based on the engineering of ion substitution. The influences of Sc3+ doping on the structure, optical and luminescence properties of LuAG:Ce were studied in detail. LuASG:Ce PCs owned blue-green emission from 510 nm to 501 nm. The emission intensity at 100 °C maintained more than 85% of the initial one, which exhibited significant thermal stability. Finally, the luminous efficacy (LE) as high as 127.59 lm/W and the emission peak at 503 nm were achieved from the LED encapsulated by Lu2.998Al4ScO12:Ce3+ with 50 W driving power. Thus, the blue-green emitting LuASG:Ce PCs will be promising phosphor converters for hp-LEDs.

Thermally Robust Orange‐Red‐Emitting Color Converters for Laser‐Driven Warm White Light with High Overall Optical Properties

AbstractLaser‐driven solid‐state lighting with super‐brightness and compactness is recognized as a promising alternative to white light‐emitting diodes. However, it is quite difficult to achieve laser‐driven warm white light with long‐term stability due to the shortage of robust orange‐ or red‐emitting laser phosphors. In this work, an efficient and thermally robust orange‐red (La,Y)3Si6N11:Ce3+ (LYSN)‐BN phosphor‐in‐glass (PiG) film is proposed to realize warm white light, where h‐BN acts as an optical medium to enhance light scattering, a heat sink to reduce the temperature, and a protective layer to prevent LYSN from oxidation. The “LYSN+15 wt.% BN” PiG film shows an internal quantum efficiency of 70% and a luminance saturation threshold of 12.82 W mm−2, much higher than those without h‐BN (i.e., 57.5% and 7.63 W mm−2). A warm white light lamp fabricated by combining “LYSN+15 wt.% BN” PiG film with blue laser diodes, showing tunable correlated color temperatures (2800–5000 K), has a maximal luminous flux of 740 lm and a luminous efficacy of 133.5 lm W−1, which promises high collimation and penetration lighting in the rainy or foggy weather. By designing a composite orange‐red‐emitting phosphor converter, this work lays a foundation for realizing high quality laser‐driven warm white lighting source.

A novel Cr3+-activated far-red titanate phosphor: synthesis, luminescence enhancement and application prospect

Plant factory, a new agricultural planting technology, has emerged and rapidly grown in recent years, with phosphor conversion light emitting diodes (pc-LEDs) considered as the first choice of source light for the plant factory. In this study, a new type of Cr3+-activated Li2MgTi3O8 phosphor (LMT: Cr3+) was synthesized by high temperature solid state method. X-Ray diffraction patterns showed that there was no detectable impurity in these samples. The photoluminescence spectra revealed that this phosphor can emit far-red light with the peak at 740 nm excited by ultraviolet and blue light, overlapped well with the PFR. After introducing Zn2+ ions (LMT: Cr3+, Zn2+), the luminescence intensity increases by 46% mainly due to the increase of lattice distortion, and internal quantum yield was improved from 25.4% to 41.3% under 365 nm excitation. Finally, the pc-LED devices, consisting of 470 nm chip coated with the optimal phosphor, exhibited good luminescence and overlapping with PFR. These results indicate that the LMT: Cr3+, Zn2+ phosphor has the potential application in modern agriculture.

Efficient transmissive remote phosphor configuration for a laser-driven high-luminance white light source.

To realize laser-driven high-luminance white light sources, many reflective configurations have been studied, often resulting in a challenging optical design. In this paper it is demonstrated that the efficacy of a transmissive configuration can be significantly enhanced by using a sapphire half-ball lens as out-coupling optic. This lens not only improves efficiency, but also drastically increases the potential light output due to improved heat dissipation from the single-crystal phosphor converter. Both claims are substantiated with detailed experimental results and realistic opto-thermal simulations, showing a light output of 6550 lm and over 20000 lm, respectively and corresponding luminance of 67 MCd/m2 and 209 MCd/m2.

Enhancing Thermal Stability of Laser-Driven Phosphor Converter by Utilizing Copper Powder Sintering Framework/Paraffin

Laser-driven white light illumination is considered as the next generation of high brightness white light source. The most common way to achieve laser-based white light is using a blue laser to excite phosphor/ silicone converter (reference converter). However, the relatively low thermal conductivity of phosphor limits most of the heat to its surface and cannot be dissipated effectively. In this work, a converter with copper sintering powder framework/paraffin (CPSF/P) embedded into the phosphor/silicone is proposed. As an internal heat transfer channel, copper powder sintering framework (CPSF) transfers heat to paraffin coated in porous skeleton, and then paraffin absorbs the generated heat through solid–liquid phase transition, which effectively dissipates the heat concentrated on the phosphor surface and improves its thermal stability. Under high-power laser excitation of 7.74 W, the surface temperature of the reference converter is up to 660 °C, while the maximum temperature of the CPSF/P converter is only 139 °C, which is reduced by 521 °C (78.9%). The results show that the proposed CPSF/P converter can withstand higher excitation power and show better thermal stability than the reference converter, which is helpful to obtain higher color stability. This provides an efficient heat dissipation scheme for high-power laser-driven lighting.

Co-sintered ceramic converter for transmissive laser-activated remote phosphor conversion

By confining a low-scattering ceramic phosphor conversion region within a high-scattering alumina substrate, we fabricated high-luminance laser-activated remote phosphor (LARP) with excellent thermal dissipation for white light generation. A dichroic mirror coating on the pump side recycles both luminescence and re-scattered pump light to improve efficacy. As a result, we demonstrated a transmissive LARP converter that achieves 600 lumens with 4.3 W of the blue pump power at an ambient temperature of 25 °C. Due to the strong cavity effect of the highly scattering substrate, a corresponding peak luminance of greater than 700 Cd/mm2 was observed. At 80 °C ambient, the converter can still achieve greater than 500 lumens and peak luminance exceeding 500 Cd/mm2. Simulations based on the optical diffusion approximation are generally in good agreement with data, although they overpredict luminous flux, suggesting the dichroic coating was not optimal and further performance improvements may be achievable.

Achieving High Light Uniformity Laser-driven White Lighting Source by Introducing Secondary Phases in Phosphor Converters

Achieving High Light Uniformity Laser-driven White Lighting Source by Introducing Secondary Phases in Phosphor Converters

Laser-excited single crystal phosphor in white LED for wide field of view and high enhanced central brightness for vehicle headlights

We demonstrate the generation of a laser hotspot by a laser-excited single crystal phosphor (SCP) converter layer in a white LED for producing a wide field of view (FOV) and high enhanced central brightness (ECB) for an adaptive-driving-beam (ADB) headlight. The SCP layer shows better thermal quench behavior than other phosphor converter layers because of the higher melting temperature of 1940 °C and larger thermal conductivity of 11 W/m°C. The advantage of this study is an optical design of the ADB headlight, in which the generation, mechanism, and characterization of the laser hotspot are investigated in detail. The proposed scheme enables a wide FOV of ±16.8° and high ECB of the high beam, compliant with the Economic Commission for Europe regulation of vehicle headlights. The wide FOV provides better visibility, while the high ECB improves the long-distance illumination of the headlights. This proposed ADB headlight is a promising headlight candidate for use in the next-generation autonomous vehicle applications.

High-speed visible light communication based on micro-LED: A technology with wide applications in next generation communication

The evolution of next-generation cellular networks is aimed at creating faster, more reliable solutions. Both the next-generation 6G network and the metaverse require high transmission speeds. Visible light communication (VLC) is deemed an important ancillary technology to wireless communication. It has shown potential for a wide range of applications in next-generation communication. Micro light-emitting diodes (μLEDs) are ideal light sources for high-speed VLC, owing to their high modulation bandwidths. In this review, an overview of μLEDs for VLC is presented. Methods to improve the modulation bandwidth are discussed in terms of epitaxy optimization, crystal orientation, and active region structure. Moreover, electroluminescent white LEDs, photoluminescent white LEDs based on phosphor or quantum-dot color conversion, and μLED-based detectors for VLC are introduced. Finally, the latest high-speed VLC applications and the application prospects of VLC in 6G are introduced, including underwater VLC and artificial intelligence-based VLC systems.

Enhancing Opto-Thermal Performances of White Laser Lighting by High Reflective Phosphor Converter

Enhancing Opto-Thermal Performances of White Laser Lighting by High Reflective Phosphor Converter

Enhancing Opto-Thermal Performances of White Laser Lighting by High Reflective Phosphor Converter

Enhancing Opto-Thermal Performances of White Laser Lighting by High Reflective Phosphor Converter

(Ce, Gd):YAG-Al2O3 composite ceramics for high-brightness yellow light-emitting diode applications

(Ce,Gd):YAG-Al2O3 composite ceramics were prepared for high-brightness yellow LED (565−590 nm) applications. Phase fraction, microstructure, thermal quenching effect, and luminescent properties of composite ceramics with varying compositions were studied in detail. Collaborating composite ceramics with InGaN blue chips, the relationship between thermal conductivity, temperature rise during LED-driven phosphor conversion, and steady-state luminous efficiency were elucidated. As the proportion of Al2O3 increases from 0 to 40 wt%, the steady-state luminous efficiency of yellow LED is enhanced from 100.88–109.49 lm W−1, benefiting from the increased thermal stability and reduced operating temperature of ceramics (from 141.1–132.2 °C). Additionally, scattering behavior and extraction efficiency of composite ceramics with different thicknesses were investigated.

A Luminous Efficiency-Enhanced Laser Lighting Device with a Micro-Angle Tunable Filter to Recycle Unconverted Blue Laser Rays.

In this work, a phosphor converter with small thickness and low concentration, based on a micro-angle tunable tilted filter (ATFPC), was proposed for hybrid-type laser lighting devices to solve the problem of silicone phosphor converters’ carbonizing under high-energy density. Taking advantage of the filter and the scattering characteristics of microphosphors, two luminous areas are generated on the converter. Compared with conventional phosphor converters (CPCs), the lighting effects of ATFPCs are adjustable using tilt angles. When the tilt angle of the micro filter is 20°, the luminous flux of the ATPFCs is increased by 11.5% at the same concentration; the maximum temperature (MT) of ATFPCs is reduced by 22.8% under the same luminous flux and the same correlated color temperature (CCT) 6500 K. This new type of lighting device provides an alternative way to improve the luminous flux and heat dissipation of laser lighting.

Reidinger defects induced thermally stable green emission from Eu2+, Mn2+ co-doped Ba0.75Al11O17.25 transparent ceramics

In this paper, Ba0.75Al11O17.25 was selected as the host for the Eu2+ and Mn2+ co-dopants due to the Reidinger defects in its lattice. Upon the 365 nm excitation, the phosphors presented the cyan to green tunable emission by changing the doping concentration of Mn2+. Moreover, this phosphor possesses zero-thermal quenching up to 448 K due to the interaction between the traps and Eu2+/Mn2+. The completely densified ceramic guaranteed the high optical transmittance (∼72 % at 516 nm) and thermal conductivity (4.3 W·m−1·K−1 at room temperature). When combined with a 6 W commercial 365 nm emitting LED chip, the temperature of the ceramic eventually stabilized at 428 K and the luminous efficacy of the LED device was almost not influenced by the thermal quenching effect. This work may open a way for exploring new phosphor conversion materials for HP/HB PC solid state lighting.

Reliable and Efficient Phosphor-in-Glass-Based Chip-Scale Packaging for High-Power White LEDs

A white light-emitting diode (WLED) with chip-scale packaging (CSP) has wide applications due to its high power density, small size, and high process integration. The phosphor converter of the CSP WLED needs to endure huge heat shock from LED chips and phosphor conversion. In this work, we proposed a phosphor-in-glass (PiG)-based CSP for high-power WLEDs. A wafer PiG was prepared by printing and sintering a phosphor glass film on a glass plate and then cut into a chip-scale PiG for the fabrication of PiG-CSP WLEDs. The optical performances of PiG-CSP WLEDs were optimized by adjusting the film thickness of PiG. Consequently, the PiG-CSP WLED emits a cool white light with optimal light performances at a film thickness of 88 μm. The related luminous efficiency (LE), correlated color temperature (CCT), and chromaticity coordinate are 108.8 lm/W, 5796 K, and (0.3256 and 0.3467), respectively. The down-PiG-CSP structure achieves higher LE and lower CCT than the up-PiG-CSP structure. Compared with the traditional phosphor-in-silicone (PiS)-CSP WLED, the PiG-CSP WLED avoids the carbonization of the converter and displays excellent thermal stability under high input current. The results determine that the PiG-CSP is a reliable and efficient packaging technology for high-power WLEDs.

Development of novel scintillation and photo-conversion materials based on Gd3(Sc,Al,Ga)5O12:Ce single crystals grown by micro-pulling-down method

Luminescence, scintillation and photoconversion properties of Gd3Al5−x−yScxGayO12:Ce crystals, grown by the micro-pulling-down method, were studied upon substitution of Al for Sc3+ and Ga3+ in the x = 1–2;y = 1–3 ranges. A decrease of the band gap and crystal field strength occurs in these garnets with increasing Sc3+ and Ga3+ content, resulted in blue-shift and reduced thermal stability of Ce3+ emission. Lowering of the scintillation light yield of crystals by two times and scintillation decay kinetic acceleration from 97 to 27 ns is observed at increasing Ga content in the y = 1–3 range. Sc and Ga admixing increases the number of deep charge traps, which additionally deteriorate of crystals scintillation performance. Application of Gd3Al5−x−yScxGayO12:Ce crystals as phosphor converters of white LED was considered. Increasing the Sc3+ and Ga3+ content in crystals leads to linear blue shift of the converter emission and results in increasing the color temperature of LEDs from neutral to could white light.

Ion-exchanged LTA zeolite derived nepheline phase NaAlSiO4:Eu2+ ceramic phosphor for laser illumination

A reliable yellow phosphor converter that can be efficiently excited by a 405 nm bluish violet laser is in high demand for laser illumination applications. A NaAlSiO4:Eu2+ phosphor with a quantum efficiency reaching 92% was obtained using LTA zeolite as the raw material. NaAlSiO4:Eu2+ ceramics with suitable porosities for laser illumination were prepared from the phosphor powders via spark plasma sintering. The ceramics lost only 2% of the quantum efficiency compared to the powders, maintained good thermal quenching properties (30% drop at 150 °C), and showed good thermal conductivity (2.02 W‧m−1‧K−1). The NaAlSiO4:Eu2+ ceramic with 405 nm bluish violet lasers, with the increase in laser power density to 9.15 W/mm2, exhibited an increasing luminous flux (23.83–70.26 lm) and maintained a stable luminous efficacy (47.7–46.8 lm/W), and the temperature distribution of the ceramic remained uniform and stable under long-time laser irradiation. This indicates that the nepheline-phase NaAlSiO4:Eu2+ ceramic is a promising material for laser illumination.

Artificial nighttime lighting impacts visual ecology links between flowers, pollinators and predators

The nighttime environment is being altered rapidly over large areas worldwide through introduction of artificial lighting, from streetlights and other sources. This is predicted to impact the visual ecology of many organisms, affecting both their intra- and interspecific interactions. Here, we show the effects of different artificial light sources on multiple aspects of hawkmoth visual ecology, including their perception of floral signals for pollination, the potential for intraspecific sexual signalling, and the effectiveness of their visual defences against avian predators. Light sources fall into three broad categories: some that prevent use of chromatic signals for these behaviours, others that more closely mimic natural lighting conditions, and, finally, types whose effects vary with light intensity and signal colour. We find that Phosphor Converted (PC) amber LED lighting – often suggested to be less harmful to nocturnal insects – falls into this third disruptive group, with unpredictable consequences for insect visual ecology depending on distance from the light source and the colour of the objects viewed. The diversity of impacts of artificial lighting on hawkmoth visual ecology alone argues for a nuanced approach to outdoor lighting in environmentally sensitive areas, employing intensities and spectra designed to limit those effects of most significant concern.

Research on Laser Illumination Based on Phosphor in Metal (PiM) by Utilizing the Boron Nitride-Coated Copper Foams.

Laser-driven illumination has unique advantages in high-power applications. Taking advantage of the valuable experience of light-emitting diodes (LED) development, phosphor in silicone (PiS) is considered to be one of the most potential commercial phosphor converter solutions for laser-driven illumination. However, the thermal quenching of the PiS converter is a bottleneck problem. Herein, a boron nitride (BN)-coated copper foam strategy is introduced for the laser-driven illumination system. The phosphor/silicone is embedded in the designed BN/copper foam to form a phosphor in metal (PiM) converter. Copper foam serves as an internal connected heat transfer channel; the BN coating solves the light absorption problem of the copper foam effectively. Based on this PiM(BN/copper foam) design, the heat dissipation is effectively improved. Under high-power laser excitation (8.13 W), the PiS converter cannot reach thermal equilibrium, and therefore the temperature increases sharply up to 660 °C. In comparison, the thermal performance of an optimized PiM(BN/copper foam) converter is able to maintain excellent stability, where the maximum temperature is only 166.5 °C. The proposed PiM strategy has a maximum temperature that is 493.5 °C lower than that of the reference PiS solution. Due to the superior thermal management, the luminous efficiency of the illumination system is constantly stable at 254 lm/W, though with less phosphor mass; and the related color temperature is about 6000 K all the time. This provides a practical and feasible heat-dissipation solution for high-power laser-driven illumination.

Phosphor converters for laser driven light sources

Due to the “efficiency droop” effect of light-emitting diodes (LEDs) under high drive currents, laser diode (LD) driven light sources are considered to replace LED lighting for the next-generation solid-state-lighting technology. In this Perspective, the history of lighting technology and the intrinsic advantages of LDs lighting are outlined. We provide a comparative overview of several typical LD phosphors, such as single crystal, transparent ceramic, phosphor-in-glass, and film thereof, as well as surface texture modification of film-type phosphor plates. The relationship between the illumination characterizations (luminance saturation, conversion efficiency, extraction efficiency, illuminating directionality, and color spatial uniformity) with thermal conductivity, pores, defects, second phases, and surface roughing or patterning is discussed. Finally, the current challenges and prospects are highlighted to provide guidelines for future research on LD phosphors.