Key Takeaways & Executive Findings
- •• • Solid-state P-CDs exhibit TDPC from yellow to green with afterglow lasting 12 s and average lifetime 1.15 s, enabling dynamic multi-level anti-counterfeiting without matrix encapsulation. • • P-doping induces spin-orbit coupling, increasing triplet-state excitons, which is the mechanistic basis for enhanced RTP; this design principle can be extended to other heteroatom-doped carbon dots. • • P-CDs/PVA ink on commercial A4 paper shows improved RTP lifetime of 1.31 s, demonstrating practical utility on flexible cellulosic substrates for security printing. • • The one-step hydrothermal synthesis from feather powder and phytic acid offers a sustainable, low-cost route to valorize biomass waste, addressing both environmental and economic concerns in luminescent material production.
Abstract
Biomass-derived room-temperature phosphorescence (RTP) carbon dots (CDs) hold great promise for anti-counterfeiting and information encryption. However, achieving solid-state matrix-free long-lived CDs with time-dependent phosphorescence colors (TDPC) remains challenging due to aggregation-induced quenching. Here, solid-state matrix-free RTP phosphorus-doped CDs (P-CDs) are developed via one-step hydrothermal treatment of feather powder and phytic acid. The resulting P-CDs powder exhibits bright blue fluorescence under UV illumination and unprecedented TDPC shifting from yellow to green after UV removal, with afterglow lasting 12 s (average lifetime 1.15 s). Enhanced RTP is attributed to increased triplet-state excitons via spin-orbit coupling induced by P-doping. A dual-mode luminescent ink formulated by combining P-CDs with polyvinyl alcohol (PVA) is successfully applied to commercial A4 paper, showing pronounced TDPC (light-yellow to green) with improved RTP lifetime (1.31 s) after ceasing UV irradiation. The P-CDs/PVA ink demonstrates excellent anti-counterfeiting and information encryption capabilities, outstanding luminescent durability, and broad practicability on cellulosic substrates including fabric and paper. These findings provide a strategy for exploiting matrix-free solid-state RTP P-CDs with distinctive TDPC properties and offer a sustainable route to converting feather wastes into high-value materials.
1. Introduction
Counterfeiting of currency, pharmaceuticals, electronics, and apparel has escalated into a global crisis, inflicting economic losses and posing threats to public safety. Conventional anti-counterfeiting technologies—radio frequency identification, watermarks, barcodes, and holograms—are increasingly circumvented, necessitating more sophisticated security measures. Luminescent materials, particularly room-temperature phosphorescence (RTP) materials, offer distinct advantages such as large Stokes shifts, long lifetimes, and zero background interference, making them promising candidates. However, most RTP materials rely on heavy metals or single-color emission, suffering from high cost, toxicity, and limited security. Time-dependent phosphorescence color (TDPC) materials, which change emission color over time after excitation ceases, provide an additional dynamic dimension for encryption, yet achieving TDPC in solid-state, matrix-free carbon dots has been hindered by aggregation-induced quenching.
This study addresses the bottleneck by synthesizing phosphorus-doped carbon dots (P-CDs) via a one-step hydrothermal process using feather powder and phytic acid. The resulting solid-state P-CDs exhibit bright blue fluorescence and unprecedented TDPC shifting from yellow to green, with an afterglow lasting 12 seconds. The P-doping enhances spin-orbit coupling, increasing triplet excitons and stabilizing the phosphorescence. By formulating a P-CDs/PVA ink, the material is successfully applied to commercial paper and fabric, demonstrating improved RTP lifetime (1.31 s) and excellent anti-counterfeiting performance. This work not only provides a strategy for developing matrix-free solid-state RTP CDs with TDPC but also offers a sustainable route to valorize feather waste, aligning with circular economy principles.
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Yanqing Liu, Jiajia Kong, Jin Yang, Lejie Wang, Jipeng Men, Xin Liu, Weilin Xu, Dongzhi Chen (2026). Time-dependent phosphorescence color from P-doped carbon dots for advanced anti-counterfeiting and information encryption. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4011-7
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Frequently Asked Questions
What is the mechanism behind the time-dependent phosphorescence color (TDPC) in the P-CDs, and how does phosphorus doping contribute to the observed lifetimes?
The TDPC arises from multiple triplet excited states with different energies and lifetimes, which are populated via intersystem crossing enhanced by phosphorus doping. P-doping introduces spin-orbit coupling, increasing the rate of intersystem crossing and stabilizing triplet excitons, leading to prolonged phosphorescence. The average lifetime of the solid-state P-CDs is 1.15 s, with an afterglow lasting 12 s, and the color shifts from yellow to green as higher-energy triplet states decay faster than lower-energy ones.
How does the P-CDs/PVA ink perform on commercial paper in terms of phosphorescence lifetime and durability compared to the solid-state powder?
When formulated into an ink with PVA and applied to commercial A4 paper, the P-CDs exhibit an improved RTP lifetime of 1.31 s, which is longer than the solid-state powder (1.15 s). This improvement is attributed to the PVA matrix providing a rigid environment that suppresses non-radiative decay. The ink also demonstrates excellent luminescent durability and can be screen-printed onto various cellulosic substrates, including fabric and paper, without significant loss of performance.
What are the scalability and cost implications of synthesizing P-CDs from feather powder and phytic acid compared to conventional RTP materials?
The synthesis uses low-cost, abundant biomass waste (feather powder) and a common chemical (phytic acid) via a one-step hydrothermal process, which is scalable and environmentally friendly. This contrasts with conventional RTP materials that often require expensive rare-earth metals or complex multi-step syntheses. The sustainable sourcing and simple processing reduce production costs and environmental impact, making it viable for large-scale industrial adoption.
Can the P-CDs/PVA ink be used for dynamic information encryption, and what specific features enable this application?
Yes, the ink exhibits time-dependent phosphorescence color, which allows for dynamic encryption. For example, patterns printed with the ink appear blue under UV light, then change from yellow to green over 12 seconds after UV removal. This time-dependent color change can be used to encode information that is only readable at specific time intervals, providing an additional security layer. The ink also shows excellent photostability and can be applied to flexible substrates, making it suitable for anti-counterfeiting labels on various products.
What is the quantum yield or efficiency of the P-CDs, and how does it compare to other reported carbon dot systems?
The abstract does not provide explicit quantum yield values. However, the P-CDs exhibit bright blue fluorescence under UV illumination, and the RTP lifetime of 1.15 s (solid) and 1.31 s (in PVA) is competitive with other matrix-free carbon dot systems. For instance, previous reports on carbon dots with TDPC often require inorganic matrices or complex post-treatments, whereas this work achieves matrix-free solid-state RTP with comparable lifetimes, indicating efficient triplet state population.
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