Core-cladding-like phosphor ceramics wafer: a path to ultra-high luminance

High-brightness laser-driven light sources, which are generated by exciting phosphor materials with high power density blue laser diodes, hold great promise for applications in long-distance searchlights, high-luminance projection displays, and long-range night vision systems. The luminance of these light sources is primarily influenced by two critical parameters: the maximum luminous flux and the illuminated area (i.e., light spot area). Both of these factors are contingent upon the properties of the phosphor materials used. The maximum luminous flux is determined by the phosphor material’s luminous efficacy and its capacity to withstand the highest blue laser power density without reaching luminance saturation. This critical limit was defined as the luminance saturation threshold. On the other hand, the blue laser light incident upon the phosphor material tends to diffuse within the bulk, leading to an expansion of the light spot. This enlargement is generally detrimental to the emitted luminance of the light sources. In essence, there is an urgent need to engineer phosphor materials that both limit light spot expansion and boost the maximum luminous flux, thereby increasing the luminance of light sources.

Recently, Professor Rong-Jun Xie’s group from Xiamen University has made a significant breakthrough: the fabrication of optical fiber-like core-cladding phosphor ceramics (CCPC), effectively addressing long-standing technical challenges and delivering ultra-high luminance performance.

The team prepared CCPC green bodies with different core diameters using the gel-casting technique. The green bodies were subsequently sintered at 2023 K for 5 hours in a vacuum environment maintained at 10⁻³ Pa. Finally, the interface between core and cladding of CCPC are tightly bonded and devoid of porosity at the interface.

The team published their work in Journal of Advanced Ceramics on July 21, 2025.

“The difference in refractive index between YAG:Ce and Al₂O₃, coupled with the non-luminescent properties of Al₂O₃, ensures that the light spot is mainly confined to the core region. This allows for precise control over the light spot area by adjusting the core dimensions” Shuxing Li, the co-corresponding author from Xiamen University. “Furthermore, the Al₂O₃ cladding, with its superior thermal conductivity compared to YAG:Ce, facilitates more efficient heat dissipation and elevates the luminance saturation threshold. Leveraging these dual advantages, the engineered CCPC of YAG:Ce@Al₂O₃ wafer can confine the expansion of the light spot area and concurrently enhance the maximum luminous flux”.

The result: The CCPC sample with a 1.0 mm core diameter exhibits a small spot size nearly identical to that of the incident blue laser beam, with a light spot expansion ratio of only 1.04. Furthermore, the high thermal conductivity of the Al₂O₃ cladding endows the CCPC with an impressive luminance saturation threshold of 30 W·mm^⁻2 and a maximum luminous flux of 2100 lm for white light within a straightforward transmissive optical setup. The combination of a confined light spot area and an elevated luminous flux results in an ultra-high luminance of 3900 lm·mm^⁻2, surpassing current reports.

“Conventional phosphor ceramics usually rely on the introduction of second-phase particles to enhance maximum luminous flux or limit the light spot area. However, there is a trade-off between these two aspects: improving one often compromises the other, which severely restricts the improvement of the output luminance of the light source” noted by Jiaochun Zheng, the first co-author from Xiamen University. “Our study not only effectively overcame these bottlenecks, but also successfully demonstrated excellent optical performance in industrial endoscope applications.”

Finally, the potential application of core-cladding phosphor ceramics in high-luminance light sources has been successfully demonstrated, providing a new research direction for the development of laser lighting technology.

The team published their findings in the Journal of Advanced Ceramics. Future work will explore applying this strategy to other ceramics, expanding the reach of Core-cladding-like phosphor ceramics in healthcare, aerospace and beyond.

About Author

Yifeng Lai received his master degree in 2024 from Xiamen University. His research interests focus on gel-casting of phosphor ceramics.

Jiaochun Zheng received his master degree in 2024 from Chengdu University. He is a Ph.D. candidate at Xiamen University. His research interests focus on rare-earth doped luminescent ceramics for high-temperature sensing.

Shuxing Li received her Ph.D. degree in 2017 from Shanghai Institute of Ceramics, Chinese Academy of Sciences (SICCAS). She was a joint training Ph.D. at National Institute for Materials Science (NIMS, Japan) from 2015-2016. She worked at Xiamen University as a postdoctoral researcher from 2017. She has been an associate professor at Xiamen University since 2023. Her research interests focus on rare-earth doped luminescent ceramics for lighting or sensing technologies.

Rong-Jun Xie received his B.S. (1992), M.S. (1995), and Ph.D. (1998) degrees from North University of China, Xi’an Jiaotong University, and Shanghai Institute of Ceramics, Chinese Academy of Sciences, respectively. He worked as a postdoctoral researcher at National Institute for Inorganic Materials (NIRIM, Japan) from 1998-2000, at National Institute of Advanced Science and Technology (AIST, Japan) from 2001-2002, and as an Alexander von Humboldt Research Fellow at Darmstadt University of Technology (TUD, Germany) from 2002-2003. He joined National Institute for Materials Science (NIMS, Japan) as a Senior Researcher in 2003. He was a Chief Researcher at NIMS until the end of 2017. Since 2018, he has been a full professor at Xiamen University. His research interests include the design, synthesis, properties, and applications of luminescent materials for solid-state lighting, emissive displays and sensing technologies.

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