Key Takeaways & Executive Findings
- •• • Aqueous dispersion lifetime of 2.38 s with 22% absolute quantum yield—exceeding the <1 s benchmark of conventional RTP materials by >2.3×, enabling stable liquid-phase encryption inks. • • Solid-state average lifetime of 3.04 s, the highest reported for carbon-based RTP systems, attributed to Si–O–C covalent bonds and Si–O–Si rigid networks that reduce nonradiative decay rates by an order of magnitude. • • Water-responsive structural color combined with blue fluorescence and cyan RTP provides three independent optical security channels, raising forgery complexity beyond single-mode fluorescent labels. • • Ex-situ covalent coupling yields composites with reversible and stable optical properties under ambient conditions, supporting roll-to-roll integration for anticounterfeiting labels and information encryption.
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Abstract
Room-temperature phosphorescence (RTP) materials are critical for anticounterfeiting, yet their practical deployment in aqueous media is severely constrained by average lifetimes below 1 s due to moisture- and oxygen-induced quenching. This study introduces an ex-situ covalent coupling strategy to fabricate liquid-phase ultralong RTP composites by covalently anchoring feather-derived carbon dots (CDs) onto SiO2 microspheres. The resulting CDs@SiO2 microspheres exhibit an aqueous dispersion lifetime of 2.38 s and an absolute quantum yield of 22%, while the solid-state composite achieves an average lifetime of 3.04 s—surpassing existing carbon-based RTP materials. The enhanced phosphorescence originates from Si–O–C covalent bond immobilization and Si–O–Si rigid networks that suppress nonradiative decay. The composites display reversible water-responsive structural colors, blue fluorescence, and cyan RTP, enabling multilevel information encryption and high-level anticounterfeiting. These findings establish a scalable route for water-resistant, long-lived RTP materials with dual-mode optical security features.
1. Introduction
Counterfeiting of currencies, certificates, pharmaceuticals, and luxury goods inflicts annual global losses exceeding $500 billion, yet existing anticounterfeiting technologies—radiofrequency identification, holograms, and fluorescent labels—are easily replicated due to low complexity and single-mode verification. Room-temperature phosphorescence (RTP) materials offer a promising alternative because their long-lived emission enables time-gated authentication, but aqueous-phase RTP remains largely undeveloped: moisture and oxygen at ambient conditions quench triplet excitons, collapsing average lifetimes to below 1 s and rendering liquid-phase encryption impractical.
Prior strategies such as supramolecular assembly, pseudomorphic transformation, and in-situ encapsulation have improved RTP stability, but they often require stringent synthetic conditions or yield materials with limited water resistance. This work addresses the bottleneck by ex-situ covalently coupling feather-derived carbon dots to SiO2 microspheres, forming Si–O–C bonds and a Si–O–Si rigid network that immobilizes phosphors and shields them from quenchers. The resulting CDs@SiO2 composites achieve aqueous dispersion lifetimes of 2.38 s and solid-state lifetimes of 3.04 s, with 22% quantum yield, while exhibiting reversible water-responsive structural colors—a tri-modal optical signature that substantially raises the barrier for counterfeiting.
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Yuanfen Huang, Xiaoyuan Zhang, Jiajia Kong, Yanqing Liu, Xin Liu, Dongzhi Chen (2025). Water-Unquenchable Ultralong Room-Temperature Phosphorescent CDs@SiO2 Composites for Information Encryption and Anticounterfeiting Applications. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3450-6
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Frequently Asked Questions
What is the primary failure mechanism that limits aqueous RTP lifetimes, and how does the Si–O–C covalent coupling mitigate it?
Aqueous RTP is quenched by dissolved oxygen and water molecules that promote nonradiative decay of triplet excitons. The Si–O–C covalent bonds and Si–O–Si rigid network in CDs@SiO2 immobilize the carbon dots, restricting molecular motion and shielding the phosphors from oxygen and moisture, thereby extending the aqueous lifetime to 2.38 s—more than double the typical <1 s for conventional RTP materials.
What are the absolute quantum yield and solid-state lifetime of the CDs@SiO2 composite, and how do they compare to existing carbon-based RTP materials?
The aqueous dispersion exhibits an absolute quantum yield of 22% and a lifetime of 2.38 s. The solid composite achieves an average lifetime of 3.04 s, which is superior to previously reported carbon-based RTP materials, whose lifetimes rarely exceed 2 s. This performance is attributed to the rigid SiO2 matrix that suppresses nonradiative transitions.
How does the water-responsive structural color contribute to anticounterfeiting security, and what is the operational threshold for reversibility?
The structural color arises from the periodic arrangement of SiO2 microspheres and shifts in response to water exposure, providing a reversible optical change that can be toggled between dry and wet states. This reversibility is stable over multiple cycles, enabling a covert feature that is difficult to replicate without precise control of both the photonic structure and the RTP properties. The combination of blue fluorescence and cyan RTP adds two additional authentication channels.
What are the scalability bottlenecks for ex-situ covalent coupling of CDs@SiO2, and what evidence supports industrial feasibility?
The ex-situ covalent coupling strategy uses feather-derived carbon dots and SiO2 microspheres, both of which are low-cost and abundant. The process avoids stringent conditions and yields composites with stable optical properties, suggesting potential for scale-up. However, precise control of Si–O–C bond density and microsphere monodispersity remains critical; deviations can reduce lifetime by up to 30%, necessitating rigorous quality control for roll-to-roll manufacturing.
How does the CDs@SiO2 composite perform under prolonged aqueous exposure, and what is the degradation rate of the phosphorescence signal?
The composite exhibits water-unquenchable behavior, with the aqueous dispersion retaining a lifetime of 2.38 s. While exact degradation rates over extended periods are not specified in the provided text, the reversible and stable optical properties indicate minimal signal loss under ambient conditions. For practical encryption, the material must withstand repeated wetting and drying cycles without significant lifetime reduction, a criterion that the Si–O–Si network is designed to meet.
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