image: The reflective S@PiGF@A color converter prepared by thermocompression bonding can withstand high laser power density and enables a maximum LF of 6749 lm@47.70 W/mm2, which is 2.44 times higher than that of the PiGF@A color converter (2522lm@19.53 W/mm2). Increasing the thickness of sapphire can effectively reduce the operating temperature of the converter, thereby improving the phosphor conversion efficiency. The findings provide valuable guidelines to design high quality PiGF color converter for high brightness laser-driven white lighting.
Credit: Journal of Advanced Ceramics, Tsinghua University Press
Laser lighting is regarded as the next generation of solid-state lighting sources due to its advantages such as high brightness, strong directionality, and long service life, showing significant potential for applications in the fields of automotive headlights, projection displays, and special lighting. Compared with traditional light emitting diode (LED) lighting, the laser diode (LD) easily achieves high brightness lighting application scenarios by increasing the power density of laser owing to the lack of the “efficiency droop” issue, providing an effective route to circumvent the physical limitations of LED lighting. Blue LD excited phosphor color converter is one of the mainstreams for laser-driven white lighting because of its adjustable emission characteristics, rich material system, and excellent cost effectiveness. Unfortunately, high power density and ultra-small spot area of blue LDs induces a significant heat accumulation in the phosphor color converter, leading to thermal quenching of the phosphor and a decrease in the luminescence saturation threshold. To alleviate heat aggregation and phosphor quenching, all-inorganic color converters have been contrived, including phosphor-in-glass (PiG), PiG film (PiGF), single crystal, and transparent ceramic. Among them, the PiGF converter containing heat-conducting substrate is regarded as an advisable choice in laser-driven white lighting owing to its remarkable advantages of design adaptability, adjustable optical properties, and simple preparation method. Although the optical and heat dissipation performances of transmissive and reflective laser lighting have been significantly enhanced by introducing the high thermal conductive substrate (sapphire, Al2O3, AlN, and Al), the commercial PiGF converters still face serious luminescence saturation at low laser power density (<15 W/mm2), which is because that the low thermal conductivity of PiGF is incapable to quickly dissipate the heat generated near the laser excitation location, thereby inducing phosphor thermal quenching and overheating gradient (ΔT > 150 K).
Recently, the team of Yun Mou from Sun Yat-Sen University, China first reported the synthesis, microstructure and photothermal properties of S@PiGF@A. The study comprehensively analyzed the photothermal properties of S@PiGF@A with different sapphire optical window thicknesses and obtained an ultra-high luminous flux of 6749lm. The study not only verified the heat dissipation enhancement mechanism of sapphire optical windows through FEA models, but also predicted that S@PiGF@A can be used as a new type of high-brightness laser lighting material.
The team published their work in Journal of Advanced Ceramics on July 29, 2025.
“In this report, we synthesized S@PiGF@A by thermocompression bonding method. The LSN PiGF is pressed between the sapphire window and the Al2O3 substrate, and no obvious crack and delamination are observed, which is prone to realize higher bonding strength and low interfacial thermal resistance. Using SEM techniques, the phosphor particles are embedded in the glass matrix of S@PiGF@A with clear phosphor-glass boundary,” said Yun Mou, associate professor at School of Integrated Circuits at Sun Yat-Sen University (China), a senior expert whose research interests focus on the field of integrated circuit (IC) process technology.
“Although the optical and heat dissipation performances of transmissive and reflective laser lighting have been significantly enhanced by introducing the high thermal conductive substrate (sapphire, Al2O3, AlN, and Al), the commercial PiGF converters still face serious luminescence saturation at low laser power density, which is because that the low thermal conductivity of PiGF is incapable to quickly dissipate the heat generated near the laser excitation location, thereby inducing phosphor thermal quenching and overheating gradient. More crucially, the internal heat dissipation enhancement mechanism of the reflective sandwich PiGF converter has not been explored yet.” said Yun Mou.
“The S@PiGF@A enables a maximum LF of 6749 lm@47.70 W/mm2, which is 2.44 times higher than that of the PiGF@A color converter (2522lm@19.53 W/mm2). The reason is that the double-sided heat dissipation channels and high heat-conducting sapphire can reduce the working temperature and thermal quenching of PiGF, thereby increasing the "effective radiation flux" (light power to thermal power ratio) available for phosphor converters. Furthermore, the LE of S@PiGF@A also increases from 127.3 lm/W to 139.5 lm/W as the sapphire thickness from 0.5 mm to 3 mm,” said Yun Mou.
The heat dissipation enhancement mechanism of S@PiGF@A was analyzed by finite element analysis. Under small spot (1.014 mm²) conditions. The operating temperature of S@PiGF@A rises sharply 0.5s before laser driving, and then stabilizes after 1s; in addition, increasing the sapphire thickness can effectively reduce the operating temperature of the converter and gradually tend to saturation, “The results indicate that the heat generated by phosphor conversion of PiGF can be quickly dissipated by high thermal conductive double-sided heat dissipation structures, thus improving the phosphor conversion efficiency.” said Yun Mou.
However, more delicate research works are still needed to explore the suitability of S@PiGF@A converters as a new material. In this regard, Mou also put forward three major development directions may be pursued in future works including the reflective substrates with higher reflectance, multi-color phosphors to improve the color rendering index, and active cooling/passive thermal conduction light-heat synergistic management design.
Other contributors include Xinyuan Wang, Jingxiang Qu, Hongjin Zhang, Deyi Chen, Ben Tian, Jianming Xu and Yang Peng. Xinyuan Wang, Deyi Chen, Ben Tian, Jianming Xu from School of Integrated Circuits, Shenzhen Campus of Sun Yat-Sen University, in Shenzhen, China; Jingxiang Qu from the School of Materials Science and Engineering Harbin Institute of Technology, in Shenzhen, China; Hongjin Zhang and Yang Peng from the school of Aerospace Engineering, Huazhong University of Science and Technology, in Wuhan, China.
This work was supported by the Key Research and Development Program of Guanzgxi Zhuang Autonomous Region (AB25069373), the Science and Technology Project of Shenzhen City (JCYJ20230807110907016), the Guangdong Basic and Applied Basic Research Foundation (2024A1515010001, 2024A1515011445), and Shenzhen Postdoctoral Research Funding Project. The authors would like to thank the Analytical and Testing Center of Sun Yat-Sen University and Huazhong University of Science and Technology for the XRD, AFM, and SEM measure supports.
About Author
Mou Yun (corresponding author), associate professor, high-level talent of Shenzhen Pengcheng Peacock Plan, and core member of the integrated circuit process team. Mainly engaged in research on advanced electronic manufacturing and integrated circuit packaging technology, including WBG semiconductor packaging, microsystem heterogeneous integration, advanced electronic packaging materials, optoelectronic devices, and MEMS device packaging. In the past five years, he directed more than 10 national and provincial level projects, including the National Natural Science Foundation of China, GF Innovation Special Zone Project, Guangxi Key R&D Program Sub Project, Shenzhen Major Science and Technology Sub Project, Guangdong Provincial Natural Science Foundation, and Shenzhen Natural Science Foundation. So far, as the first/corresponding author, he have published 26 papers in international first-class journals such as Energy Convers. Manage., J. Adv. Ceram., IEEE Electron Device Lett., applied for more than 20 national invention patents, and served as a guest editor for Micromachines journal and multiple journal reviewers.
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
Journal
Journal of Advanced Ceramics
Article Title
A reflective sapphire@PiGF@alumina color converter enabling ultrahigh luminescence laser-driven white lighting
Article Publication Date
29-Jun-2025