Solid-state Laser Lighting Research Articles

Fabrication and luminous properties of BaAl2O4-LuAG:Ce composite phosphor ceramics for solid-state laser lighting

Based on the “effective ionic radius match effect” and the “charge balance substitution rule of ions”, mixed Ba2+, Al3+, Lu3+, and Ce3+ ions can be effectively regulated to a BaAl2O4-LuAG:Ce biphasic structure. The contribution of BaAl2O4 like as scattering centers can reduce overall reflection losses and enhance the light extraction efficiency of these composite phosphor ceramics (CPCs). In this work, a series of x wt.% BaAl2O4-LuAG:Ce (x = 0, 3, 5, 10, 15) CPCs were fabricated by vacuum sintering using co-precipitated composite powders. Homogenization at the atomic level of mixed Ba3+, Al3+, Lu3+, and Ce3+ ions in multiphase powders provides uniform distribution of BaAl2O4 and LuAG:Ce constituent phases in composite ceramics. The introduction of BaAl2O4 has an additive effect, which also consists in uniform aggregation of pores near their grains during sintering. It allows to adjust the size and amount of microstructural defects by varying the secondary phase content. Under the excitation of 10.8 W 450 nm LDs in a reflection mode, 3 wt% BaAl2O4-based CPCs show the optimum luminous flux of 2244 lm and a luminous efficiency of 208 lm·W−1. The obtained CPCs show a high application potential in solid-state laser lighting.

Double Perovskite Single Crystals with High Laser Irradiation Stability for Solid-State Laser Lighting and Anti-counterfeiting.

Laser lighting devices, comprising an ultraviolet (UV) laser chip and a phosphor material, have emerged as a highly efficient approach for generating high-brightness light sources. However, the high power density of laser excitation may exacerbate thermal quenching in conventional polycrystalline or amorphous phosphors, leading to luminous saturation and the eventual failure of the device. Here, for the first time, we raise a single-crystal (SCs) material for laser lighting considering the absence of grain boundaries that scatter electrons and phonons, achieving high thermal conductivity (0.81 W m-1 K-1) and heat-resistance (575 °C). The SCs products exhibit a high photoluminescence quantum yield (89%) as well as excellent stability toward high-power lasers (>12.41 kW/cm2), superior to all previously reported amorphous or polycrystalline matrices. Finally, the laser lighting device was fabricated by assembling the SC with a UV laser chip (50 mW), and the device can maintain its performance even after continuous operation for 4 h. Double perovskite single crystals doped with Yb3+/Er3+ demonstrated multimodal luminescence with the irradiation of 355 and 980 nm lasers, respectively. This characteristic holds significant promise for applications in spectrally tunable laser lighting and multimodal anticounterfeiting.

Fabrication and luminescence properties of Al2O3-Ce:LuAG composite phosphor ceramics for solid-state laser lighting

Introducing Al2O3 as a secondary phase into Ce:LuAG phosphor ceramics has been realized by solid-state reaction method, but there is much room for improvement on the ingredient uniformity and performance of Al2O3-Ce:LuAG composite phosphor ceramics (CPCs). In this work, the excess of Al3+ in (Ce,Lu)3Al5O12 was regulated to synthesize a series of Al2O3-Ce:LuAG multiphase powders by the co-precipitation method, and homogeneous Al2O3-Ce:LuAG CPCs (the uniform volume fraction between Al2O3 and Ce:LuAG phases) were obtained by vacuum sintering (1775 °C × 10 h). With an increase in the Al3+ content, the morphology of the multiphase powders changes from small irregular shapes to porous flocs and flakes interwoven, and Lu3Al5O12 phases tend to convert to LuAlO3 phases. When the Al2O3 content is 78–89 mol% in the CPCs, the average grain sizes of Al2O3 are close to those of Ce:LuAG. Among all CPCs with an Al2O3 content of 68–95 mol%, the 85 mol% Al2O3-Ce:LuAG CPCs initially perform the best in terms of both excitation and emission intensity at room temperature, and their photoluminescence intensities only decrease 4.3% from 25 to 225 °C. A solid-state laser lighting device was constructed by using a 450 nm laser source and Al2O3-Ce:LuAG CPCs in a reflection mode. The CPCs with 85 mol% Al2O3 content based on 0.9 W laser diodes (LDs) show the optimum luminous flux (LF) and luminous efficiency (LE) of 244 lm and 266 lm∙W−1, respectively. Additionally, the LF of all CPCs based on LDs continues to increase without showing luminescence saturation when the power density increases from 1 to 20 W mm−2. When the 85 mol% Al2O3-containing CPCs are excited by a 20 W mm−2 LD, the maximum LF reaches 3624 lm, and the LE decreases only by 12.4% (compared to the data under 1 W mm−2 excitation). Al2O3-Ce:LuAG CPCs have excellent luminescence properties and improved thermal stability, which are promising for the application in solid-state laser lighting.

Development of a 2 μm Solid-State Laser for Lidar in the Past Decade.

The 2 μm wavelength belongs to the eye-safe band and has a wide range of applications in the fields of lidar, biomedicine, and materials processing. With the rapid development of military, wind power, sensing, and other industries, new requirements for 2 μm solid-state laser light sources have emerged, especially in the field of lidar. This paper focuses on the research progress of 2 μm solid-state lasers for lidar over the past decade. The technology and performance of 2 μm pulsed single longitudinal mode solid-state lasers, 2 μm seed solid-state lasers, and 2 μm high power solid-state lasers are, respectively, summarized and analyzed. This paper also introduces the properties of gain media commonly used in the 2 μm band, the construction method of new bonded crystals, and the fabrication method of saturable absorbers. Finally, the future prospects of 2 μm solid-state lasers for lidar are presented.

The Spotlight Based on the Solid-State Laser Light Source

The spotlight development on the solid-state laser light source is considered in this scientific article. The light sources characteristics are as close as possible to the characteristics and parameters of modern LED light sources. The main aim is to reach the luminous flux value of 3000 lm. That is analogues with the luminous flux of modern LED searchlights. As well as the photometric and electrical parameters, values and determination of the measures to improve the design of the spotlight are of the interest. The spotlight sample has been tested. And the test results show that after the value of 3000 lm reached the main failing of light source is the low value of its luminous efficacy, equal to 57 lm/W. In order to increase the light output of the searchlight, there are the ways of modernization of its construction suggested in the article. The previous results show that the measures suggested will allow us to increase the value of luminous efficacy to 100 lm/W. Besides that, such parameters and characteristics of the spotlight as the correlated colour temperature (CCT), colour rendering index (CRI), wattage, luminous intensity and spectral light distribution are measured and submitted in the article. The obtained energetic characteristics of the sample allow us to conclude that application of such light sources is approved in special conditions. Absence of electronic components in the distant radiation source of white light allows increasing the light source reliability substantially. Therefore, the laser spotlights are acceptable for application in the hard-to-reach places for installation of the lighting equipment, for example, on high places where the equipment demount used for repairing works is too difficult. It is actually to use also the developed light sources at the explosive industrial facilities having the current-transmitting elements of construction, especially having the open contacts. That allows reducing the safety of facility operation significantly.

Significant enhancement of luminescence properties of YAG:Ce ceramics by differential grain sizes control

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al2O3–YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al2O3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting.

Ce:GdYAG phosphor-in-glass: An innovative yellow-emitting color converter for solid-state laser lighting

• High quality yellow-emitting Ce:GdYAG PiG can be successfully synthesized by a facile solid-state sintering method. • Ce:GdYAG PiG presents an excellent IQE of 91% and a high thermal conductivity of 1.844 W m −1 K −1 . • Ce:GdYAG PiG displays a LE of 163.5 lm/W, high CRI of 74.8 and low CCT of 4806.8 K under blue laser excitation. • The color of the modular LDs (constructed by Ce:GdYAG PiG) converts from blue to yellow which realizes chromaticity adjustment easily. Stable, efficient and high color rendering index all-inorganic color converters are urgently demanded for white laser diodes. Phosphor-in-glass (PiG), possessing the advantages of phosphors excellent quantum efficiency as well as favourable chemical and thermal stability of glass, has attracted widespread attention. There have been only very few reports of Y 1.31 Ce 0.09 Gd 1.6 Al 5 O 12 (Ce:GdYAG) PiG for solid-state laser lighting. Herein, a series of Ce:GdYAG PiG samples are fabricated by a simple solid-state sintering method. Impressively, the supreme internal quantum efficiency of as-prepared PiG is 91%, which is very close to original phosphors (95%). Furthermore, PiG exhibits a high thermal conductivity (1.844 W m −1 K −1 ) and a maximum transparency (62%). Remarkably, by changing the concentration of phosphors and the thickness of PiG samples, a luminous efficacy of 163.5 lm/W, high color rendering index of 74.8 and low correlated color temperature of 4806.8 K are achieved under blue laser irradiation. These results indicate that the Ce:GdYAG PiG samples have shown tremendous application foreground as all-inorganic color converter for solid-state laser lighting.

Targeting cooling for YAG:Ce3+-based laser-driven lighting device by blending high thermal conductivity AlN in phosphor-sapphire composite

Thermal stability and heat dissipation of all-inorganic color convertors are the key obstacles for high-power laser-driven lighting devices. Herein, we proposed an efficient heat dissipation approach to solve these issues by blending high thermal conductivity AlN in a YAG:Ce3+-based phosphor-sapphire composite (abbreviated as PSC) plate. Notably, the most elevated surface working temperature of the AlN-filled PSC (AlN-PSC) is dramatically decreased by 266.9 °C at a blue laser power density of 10.99 W/mm2 compared with that of without AlN-filled PSC (AlN-Free-PSC), implying that the AlN particles effectively acted as heat transfer channels to dissipate the accumulated heat to ambient air and sapphire substrate. Benefitting from the AlN particles also act as scattering centers, a transmissive mode solid-state laser lighting device was fabricated using 10 wt% AlN-PSC and 442 nm blue laser, which maintains a luminous efficacy of 133 lm/W and a luminous flux of 1000 lm without sacrificing the optical performance in comparison with AlN-Free-PSC based white LDs. The proposed method aims at enhancing the heat removal in phosphor glass films and may lead to the development of adding other new reinforcing fillers with high thermal conductivity in heat-conducting PSC.

High efficiency green-emitting phosphor-in-glass films for high-power solid-state laser lighting

The next generation of solid-state lighting technology driven by laser diodes (LDs) is in full development, and the way green fluorescent materials with narrow-band emission (such as β-Sialon) exert their inherent potential in laser displays and projectors has attracted public interest. In this paper, stable borosilicate glass was utilized as an inorganic binder to prepare phosphor-in-glass films (PiFs) by cosintering sapphire and β-Sialon phosphor. There was no interface reaction between the glass and the phosphor, and the phosphor was uniformly and nondestructively distributed in the composite film closely attached to the sapphire. The optimized PiFs achieved an internal quantum efficiency of 76% and a thermal conductivity of 8.6 W m−1K−1, and a thermal diffusivity of 2.6 mm2 s−1 demonstrated their excellent thermal stability. A beam of high-purity light with a brightness of 887 lm and a luminous efficiency of 183 lm/W was achieved under 450 nm blue LD radiation, which is the relatively superior performance by β-Sialon series luminescent materials in an LD application reported thus far. We believe that in the near future, strategies such as adjusting glass composition, improving quantum efficiency, and sample postprocessing will further improve the performance of β-Sialon phosphors with narrow-band emission to make new contributions in the field of high-quality lasers.

SrAlSiN3:Eu2+ containing phosphor-in-glass: A color converter for solid state laser lighting

In this work, we report a kind of red emitting phosphor-in-glass (PiG) with low sintering temperature which is more conducive to prevent the denaturation of SrAlSiN3:Eu2+ (SASN:Eu2+) caused by the interface reaction between glass and phosphor. In addition, the PiG contains high content (80 wt%) of phosphor powders, which is beneficial to high power density light excitation. Under the 450 nm excitation the PiG sample showed an internal quantum efficiency value of up to 75.6%, which is close to that of the original powder SASN:Eu2+ (∼82.3%). When driven by a 1 W blue LD, the luminous efficacy of PiG reached 94 lm/W. The glass powder used as the matrix for PiG is borosilicate glass prepared from LTA zeolite and boron oxide. This glass has good optical properties and chemical stability.

Y2O3-YAG:Ce composite phosphor ceramics with enhanced light extraction efficiency for solid-state laser lighting

Optimized Y2O3-YAG:Ce composite phosphor ceramics with designed microstructures were prepared and well suited for solid-state laser lighting with high power and brightness.

High color rendering index composite phosphor-in-glass for high-power white laser lighting

The aim of this study is to investigate a thermally robust white color converter for high-power solid-state lighting, especially laser lighting. Lu3Al5O12:Ce3+/CaAlSiN3:Eu2+ phosphor-in-glass samples (LuAG&CASN-PiGs) were synthesized via a low temperature co-sintering technique. The prepared LuAG&CASN-PiGs exhibited remarkably high internal quantum efficiency of 87 %. Tunable warm white light-emitting diodes (wLED) were acquired by tailoring the sample thicknesses and phosphor contents. The optimized sample showed a high luminous flux of 183.68 lm under a blue laser diodes (LDs). In addition, the chromaticity of white LDs based on the LuAG&CASN-PiGs shifted from cool to warm white by changing the sample thicknesses. High quality white light in wLDs was achieved (Ra＝95). More importantly, the constructed LuAG&CASN-PiG converted LDs with a heat sink exhibited the luminous efficiency of 216.79 lm W−1. The results revealed that the prepared LuAG&CASN-PiG had great potential for application in solid-state laser light sources.

A unique green-emitting phosphor-in-glass (PiG) for solid state laser lighting and displays

To further demonstrate the potential for solid-state laser lighting applications, the optical performances of (BaSr)2SiO4–PiG are explored under blue laser irradiation.

Phosphor-in-glass (PiG) plates for blue laser diode driven white-light emission

Abstract Owing to the great thermal stability, phosphor-in-glass (PiG) is a promising color converter for the laser diode (LD) excitation based high-power white light-emitting LDs. Here, we reported the rapidly developed PiG plates using a facile microwave irradiation technique where the YAG:Ce3+ phosphor embedded with soda-lime silica glass. The effects of phosphor content and microwave irradiation energy were studied for investigating the optimal performance of PiG plate. To evaluate the practical applicability, the luminescence and thermal properties of the PiG plate was compared with the commercial YAG:Ce3+ single-crystal. The PiG plate and YAG:Ce3+ single-crystal individually combined with blue LD exhibited the white light with the CIE color coordinates of (0.3016, 0.3098) and (0.3254, 0.3555), respectively. The maximum surface temperature of the PiG plate was found to be about 96.1 °C, which is much lower than the YAG:Ce3+ single-crystal of 124 °C. The change in the CIE color coordinate of the PiG with aging time is smaller than that of YAG:Ce3+ single-crystal. This PiG plate might provide an important implication to overcome current limitation of LD driven solid state laser lighting.

Fabrication and luminous properties of phosphor ceramic for application in automotive laser headlight

We report on the optimization of fabrication of a ceramic phosphor plate (CPP) using α-Al2O3 as functional materials for an automotive laser headlamp. The prepared CPP shows the high luminous characteristics with increasing α-Al2O3 contents because of the light scattering of the hexagonal structure of α-Al2O3 materials. We investigated the correlation between α-Al2O3 and thickness of CPP. The luminous properties of the CPP are improved and optimized according to the variables of one. We found that the prepared sample is a potential material for future solid-state laser lighting in application as an automotive headlamp.

The effect of the porosity on the Al2O3-YAG:Ce phosphor ceramic: Microstructure, luminescent efficiency, and luminous stability in laser-driven lighting

Solid-state laser lighting (SSL) fabricated by integrating laser diode with phosphor is a new development to achieve high luminance. Because of the high temperature caused by the laser, the phosphor-conversion apparatus is demanded to possess excellent thermal properties. In this paper, we utilized spark plasma sintering (SPS) to prepare the Al2O3-YAG:Ce phosphor ceramics with outstanding performances. Due to the high thermal conductivity and high transmittance, a high saturation input power (32 W/mm2) can be achieved for the sample with the lowest porosity. The correlated color temperature (CCT) and color rendering index (CRI) of composite ceramics with the lowest porosity are stable as the input power increases from 0.7 W/mm2 to 30.8 W/mm2. Nevertheless, the sample with the highest porosity shows the highest luminescence efficiency (305 lm/W) and luminous emittances (1796 lm/mm2), which can be ascribed to the scattering of the pore.

Improving the luminous efficacy and resistance to blue laser irradiation of phosphor-in-glass based solid state laser lighting through employing dual-functional sapphire plate

The luminous efficacy and durability of white LDs are obviously enhanced though employing dual-functional sapphire plate.

High luminous fluorescence generation using Ce:YAG transparent ceramic excited by blue laser diode

Solid-state laser lighting is an emerging technology, whereby high-brightness white light can be generated using blue laser diodes combined with a yellow-emitting phosphor. In this study, Ce:YAG transparent ceramic wafers with different cerium concentrations and thicknesses are prepared and their optical characteristics are measured. A transmission mode is used, wherein the phosphor ceramic is fixed onto an oxygen-free copper sink, whose temperature is accurately controlled, and excited using the blue laser diode. The recorded spectrum shows that blue laser light is completely converted to yellow light with a wavelength of 565 nm and width of 200 nm. Moreover, with varied temperatures of 10–80 °C, the luminous flux, spectrum, and color coordinates exhibit relatively stable. More importantly, the luminous flux is highest (2690 lm) when irradiated by a 19.5-W blue laser (with a center wavelength of 454 nm) for a Ce3+ dopant concentration of 0.5 mol% and a Ce:YAG thickness of 1.6 mm. Based on these results, the Ce:YAG transparent ceramic can be used as a potential phosphor material in applications of high-power solid-state laser lighting and laser display.

Composite ceramic with high saturation input powder in solid-state laser lighting: Microstructure, properties, and luminous emittances

Solid-state laser lighting produced by blue laser diode (LD) and yellow-emitting phosphor converter materials is an exciting new development. The great flux from the laser diode results in self-heating, which lead to high temperature, thus new phosphor geometries are required. In this paper, the Al2O3–YAG: Ce phosphor ceramics with high saturation input powder were prepared by spark plasma sintering (SPS). The phase fraction, microstructure, and luminescent properties of ceramics with varying composition were investigated. High luminous emittance (1888 lm/mm2) could be reached when the composite phosphor ceramics was applied in laser lighting. In our work, high thermal conductivity, high quantum efficiency, and suitable transmittance play a vital role to obtain ceramic with high saturation input powder. In addition, for the evolution of microstructure, a new model has been established to foretell the thermal conductivity.

Pore-existing Lu3Al5O12:Ce ceramic phosphor: An efficient green color converter for laser light source

Lu3Al5O12:Ce (LuAG:Ce) ceramic - a super-duper green color converter was fabricated by a solid-state reaction method under vacuum. The sintering temperature was adjusted to control the pore characteristics, which would cause different degrees of scattering. Microstructures of ceramics sintered at different temperatures were observed by scanning electronic microscopy (SEM). Photoluminescence (PL) of the ceramics was characterized by a fluorescent spectrophotometer. It was found that the micro-sized pores inside the ceramics play a key role in optimizing the PL intensity. Under the blue laser (450 nm) excitation, the optimized sample with a porosity of 2.88% showed high luminous efficiency of over 200 lm/W and high thermal stability of luminescence. The light conversion efficiency was 50.2% and 44.4% in the dynamic and static mode, respectively. The results highlighted that the prepared ceramics had great potentials for application in solid state laser light source (LLS).