Glass-crystallized far-red-emitting ceramics for high-power, spectrally matched plant-growth light sources

In recent years, luminescent transparent ceramics have attracted increasing attention as promising candidates for next-generation solid-state light sources. However, the enhancement of luminous efficiency is usually realized at the expense of thermal stability or structural integrity of the ceramics. Therefore, obtaining both high quantum efficiency and excellent thermal resistance is of great importance. In this study, highly efficient Cr³⁺-doped silicate ceramics were fabricated by a glass-crystallization route, and their optical and structural performances were optimized through rational cation substitution engineering.

A research group led by Guojun Zheng from Ningbo University in Ningbo, China recently developed far-red emitting Cr³⁺-activated ceramics by a pressureless glass-crystallization method. The homogeneous microstructure composed of large garnet grains and uniformly distributed Cr³⁺ activators provided a stable luminescence center and efficient radiative transition pathway, which contributed to the enhancement of emission intensity. Moreover, they have successfully realized tunable luminescent and thermal properties of the ceramics through Ba²⁺ substitution for Ca²⁺, enabling the emission spectrum to match well with the absorption band of phytochromes.

The team published their work in Journal of Advanced Ceramics on August 24, 2025.

“Metal ion substitution is effectively applied to regulate the luminescence performance of garnet ceramics. Specifically, Cr³⁺ ions are highly sensitive to variations in the crystal field environment and exhibit stable incorporation into octahedral sites, which makes it easier for ions to be doped into the lattice of Y₂CaAl₄SiO₁₂, leading to enhanced radiative transitions. In addition, the spectral tunability of Cr³⁺ in the garnet lattice is closely related to the radius of the substituent cations, and a rational doping concentration is essential for achieving efficient emission levels. Ba²⁺ ions possess a larger radius than Ca²⁺ ions and show high solubility. This substitution is favorable for increasing the crystal field strength of Cr³⁺, leading to the formation of narrow-band far-red emission.” said Guojun Zheng, senior author of the study.

The researchers used a glass-crystallization method to fabricate Cr³⁺-doped Y₂Ca_1-xBa_xAl₄SiO₁₂ ceramics under a weakly reducing atmosphere. The team evaluated the luminescent properties of the ceramics with different Ba²⁺ contents, optimized the crystallization process, and obtained the optimum composition of Y₂Ca_0.3Ba_0.7Al₄SiO₁₂:Cr³⁺. The experiments showed that the optimized ceramic exhibited nearly unity internal quantum efficiency (~97%) and excellent thermal stability with a 99% emission intensity retention at 150 °C, which is significantly higher than conventional phosphor-in-silicone converters. In addition, the resulting ceramic-based pc-LED demonstrated a high wall-plug efficiency of 27%, while the laser-driven device achieved a record output power of 2.1 W, highlighting its potential for high-power plant lighting.

Furthermore, the researchers explained the mechanism of the improved luminescent performance. The Ba²⁺ substitution enlarged the lattice volume and strengthened the local crystal field around Cr³⁺ ions, which tuned the emission spectrum from a broad near-infrared band to a narrow far-red band overlapping with the absorption of phytochrome P_fr. Moreover, the highly dense ceramic microstructure reduced light scattering and nonradiative recombination, thereby increasing the effective absorption and further enhancing the light conversion efficiency.

This work was supported by the National Natural Science Foundation of China (Nos. 12304443 and 12104398), the Natural Science Foundation of Zhejiang Province (No. LMS25F050010), the Ningbo Natural Science Foundation (No. 2024J221), and the Scientific Research Fund of Zhejiang Provincial Education Department (No. Y202456622).

About Author

Guojun Zheng is a Specially-Appointed Associate Professor and Master's Supervisor at Ningbo University who obtained his Ph.D. in Engineering from the School of Optical Science and Engineering, Zhejiang University in 2023. His research focuses on inorganic optoelectronic functional materials and devices, including near-infrared fluorescent materials for intelligent non-destructive detection technologies and fluorescent ceramics for high-power solid-state lighting applications. He has led research projects such as the National Natural Science Foundation of China Youth Program and Zhejiang Provincial Natural Science Foundation, and has published 10 SCI papers as first or corresponding author in prestigious journals including Advanced Materials, Advanced Science, Laser & Photonics Reviews, and Advanced Optical Materials.

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