In the quest for brighter, more efficient laser-driven lighting, scientists have long grappled with a persistent challenge: as laser power density increases, light output plateaus while material temperatures soar. What causes this "saturation dilemma"? Is it purely optical quenching, thermal runaway, or a complex interplay? A groundbreaking study published in the Journal of Advanced Ceramics provides the first comprehensive explanation, using LuAG:Ce thin films as a model system.
The team published their work in Journal of Advanced Ceramics on February 9, 2026.
Led by Professor Shaohong Liu from Northeastern University's School of Materials Science and Engineering, the team systematically varied Ce doping concentrations (0.1-4.0 mol%) and employed active water-cooling experiments to dissect the underlying mechanisms. Key findings include:
Heat Sources Identified: Heat isn't an external factor but an inherent byproduct of the light-to-light conversion process. Photoluminescence excitation/emission (PLE/PL) spectra show a ~0.28 eV Stokes shift, converting about 10% of absorbed blue laser energy into heat per photon. This escalates with higher Ce concentrations and power densities.
Critical Ce Concentration Threshold: At 2.5 mol% Ce, a mechanistic shift occurs. Below this, the material behaves like an ideal solid solution with minimal lattice strain, high saturation thresholds (28-40 W/mm 2 ), and heat mainly from Stokes shifts. Above it, lattice parameters deviate from Vegard's law, strain surges, and concentration quenching via dipole-dipole interactions kicks in, dropping thermal quenching activation energy from 0.3 eV to 0.15 eV. This amplifies heat, accelerates non-radiative transitions, and lowers saturation thresholds.
Essence of Saturation: Luminous saturation arises from non-radiative recombination channels dominating energy competition. Low Ce (0.1-0.5 mol%) offers thermal stability but low brightness due to weak absorption. Optimal Ce (0.8-2.5 mol%) peaks at 1618.3 lm under 28 W/mm 2 . High Ce (≥3.0 mol%) causes rapid temperature rises and efficiency drops.
Decisive Proof via Cooling: Active water-cooling, without altering absorption (~1% fluctuation), reduced spot temperatures by ~42.3 °C at 2.5 mol% Ce. This delayed saturation from 28 to 32 W/mm 2 and boosted maximum flux by 19.8% to 1938.6 lm, proving heat-induced non-radiative processes—not optical saturation—are the culprit.
"This work goes beyond material fabrication; it establishes a universal design principle for high-energy-density lighting," said Professor Liu. "The key to breaking brightness limits lies in blocking non-radiative energy 'leaks' through synergistic control of energy flows."
The study paves the way for ultra-high-flux laser lighting in applications like automotive headlights, projectors, and displays. Future efforts will focus on advanced thermal management and doping strategies.
About Author
Prof. Shaohong Liu is a Professor and Doctoral Supervisor at the School of Materials Science and Engineering, Northeastern University. He is a member of the Academic Committee of Precious Metals of the China Nonferrous Metals Society and serves as a Youth Editorial Board Member for the Chinese Journal of Luminescence (发光学报), Chinese Journal of Rare Metals (稀有金属), and Rare Metals. He is also a reviewer for several international journals, including Chem. Commun., J. Mater. Chem., Langmuir, Ceram. Int., and J. Alloy Compd.
Prof. Liu has received numerous awards, including the Second Prize of the Liaoning Provincial Natural Science Award, the First Prize of the Liaoning Provincial Natural Science Academic Achievement Award, the Second Prize of the China Nonferrous Metals Science and Technology Paper Award, and the Excellent Doctoral Dissertation of Northeastern University.
His research interests encompass a wide range of materials science and engineering topics, including precious metal sputtering targets for semiconductors (Ru, Ir), AgCuTi series brazing fillers, AgMgNi electrical contact materials, laser lighting technology, ceramic copper-clad substrates, and ceramic/metal joining.
Prof. Liu has published over 60 research papers in domestic and international academic journals, including the Journal of Advanced Ceramics, Journal of Materials Science and Technology, Journal of Materials Chemistry A, Chemical Engineering Journal, and Rare Metals. He also holds 7 granted national invention patents as the first inventor.
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 of Advanced Ceramics
Origins of heat and luminous saturation in LuAG:Ce thin films for high-power laser lighting
4-Jan-2026