Key Takeaways & Executive Findings
- •• • Achieved a high luminescence dissymmetry factor (g_CPA) of up to 0.74, significantly exceeding typical values for conventional CPA materials, enabling strong circular polarization contrast for imaging applications. • • Demonstrated a long visualization time of 7 minutes, far surpassing typical organic afterglow materials, which is critical for persistent imaging and optical storage. • • Developed processable, full-color CPA materials by embedding inorganic phosphors (Y2O2S:Eu,Mg,Ti, SrAl2O4:Eu,Dy, Sr2MgSi2O7:Eu) in cholesteric liquid crystal polymers, overcoming compatibility issues and enabling practical patterning. • • Implemented circular polarization differential imaging (CPDI) using the CPA materials, providing a novel imaging technique that leverages circular polarization for enhanced contrast and information content.
Abstract
Circularly polarized afterglow (CPA) materials provide an advanced optical signature to light emission, offering great potential for advanced photonic technologies. However, practical implementation remains challenging due to the lack of satisfactory performance, that is, high luminescence dissymmetry factor (g_CPA), long visualization time, and good processability. Here, we develop processable, full-color CPA materials composed of cholesteric liquid crystal polymers (CLCPs) and inorganic phosphors embedded in polymers, achieving a high g_CPA value of up to 0.74 and a long visualization time of 7 min. The materials are constructed with a bilayer structure comprising CLCPs and inorganic luminophors such as Y2O2S:Eu,Mg,Ti, SrAl2O4:Eu,Dy, and Sr2MgSi2O7:Eu. The CLCPs are synthesized from polymerizable liquid crystal monomer RM257, chiral dopants R/S5011, dipropylamine, photoinitiator Irgacure 651, cross-linker PETMP, and chain extender. The resulting materials exhibit excellent circularly polarized optics, enabling the implementation of circular polarization differential imaging (CPDI), where images are generated by subtracting two images captured through left- and right-handed circularly polarized filters. This work demonstrates the unique application of CPA in imaging, opening a new pathway for the use of purely inorganic solid-state luminophors in chiral functional materials.
1. Introduction
Afterglow materials, which exhibit persistent emission visible to the naked eye, have expanded the dimensionality of optical signals and garnered significant interest in photonic fields. However, conventional afterglow materials lack circular polarization, limiting their utility in advanced applications such as 3D displays and biological imaging. The introduction of circular polarization to afterglow—termed circularly polarized afterglow (CPA)—adds a new dimension beyond color and lifetime, yet existing strategies suffer from low luminescence dissymmetry factors (g_CPA) and poor processability.
Recent advances have shown that coupling luminophors with cholesteric liquid crystals can enhance g_CPA values, but compatibility issues between organic luminophors and liquid crystals often lead to instability and weak processability. Moreover, organic afterglow materials typically exhibit short visualization times, hindering practical implementation. This work addresses these bottlenecks by employing purely inorganic phosphors embedded in cholesteric liquid crystal polymers, achieving a high g_CPA of 0.74 and a visualization time of 7 minutes, while maintaining processability. The developed materials enable circular polarization differential imaging, demonstrating a practical application in imaging.
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ZHAO Shanshan, ZHANG Mingjiang, TONG Zhi, LI Anqi, LI Tiehao, ZHUANG Taotao (2026). Chiral Afterglow Materials for Imaging: High Dissymmetry Factor and Long Visualization Time via Cholesteric Liquid Crystal Polymers and Inorganic Phosphors. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3928-4
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Frequently Asked Questions
What is the maximum g_CPA value achieved and how does it compare to conventional CPA materials?
The maximum g_CPA value achieved is 0.74, which is significantly higher than typical values for conventional CPA materials (often below 0.1). This high dissymmetry factor is crucial for applications requiring strong circular polarization contrast, such as in circular polarization differential imaging.
How long is the visualization time and what factors contribute to this extended duration?
The visualization time is 7 minutes, which is exceptionally long compared to organic afterglow materials that typically last only seconds. This is attributed to the use of inorganic phosphors (e.g., SrAl2O4:Eu,Dy) known for their long persistent luminescence, combined with the protective polymer matrix that prevents quenching.
What are the key components in the CLCP matrix and how do they influence the material's properties?
The CLCP matrix is composed of RM257 (polymerizable liquid crystal monomer), R/S5011 (chiral dopants), DPA (dipropylamine), Irgacure 651 (photoinitiator), PETMP (cross-linker), and a chain extender. The chiral dopant induces a helical structure, enabling selective reflection and circular polarization. The cross-linker and chain extender enhance mechanical stability and processability.
How is the circular polarization differential imaging (CPDI) technique implemented and what advantages does it offer?
CPDI is implemented by capturing two images through left- and right-handed circularly polarized filters and subtracting them. This technique leverages the circular polarization of the afterglow to generate images with enhanced contrast and information, enabling unique applications in imaging that are not possible with unpolarized light.
What are the potential scalability and cost implications of using inorganic phosphors in CLCP matrices?
Inorganic phosphors are generally more stable and less expensive than organic afterglow materials, and the fabrication process is compatible with standard polymer processing techniques. This suggests potential for scalable production at lower cost, though specific cost data is not provided in the text.
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