Unclonable anticounterfeiting application of green emissive carbon quantum dots derived from spent oolong tea leaves : Carbon quantum dots from waste materials for anti-counterfeiting

Wu, Fangling (2023) Unclonable anticounterfeiting application of green emissive carbon quantum dots derived from spent oolong tea leaves : Carbon quantum dots from waste materials for anti-counterfeiting. In: ISS:IQP - International Summer School in Integrated Quantum Photonics, 2023-07-19 - 2023-07-26, Bristol.

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Abstract

This work presents a sustainable route to fluorescent carbon quantum dots (CQDs) derived from waste oolong tea leaves and explores their potential for anti-counterfeiting and optical physical unclonable function (PUF) applications. The aim is to transform biowaste into functional nanomaterials capable of generating unique optical fingerprints for secure identity encoding. CQDs were synthesised hydrothermally from waste tea leaves, providing an environmentally friendly approach without additional surface modification, and were subsequently deposited onto SiO₂ substrates for structural and optical characterisation. Atomic force microscopy shows that the CQDs are predominantly distributed between 1.7 and 6.0 nm, with an average diameter of approximately 5 nm based on analysis of more than 100 particles. Optical measurements reveal a strong UV–vis absorption peak at 273 nm with a shoulder around 298 nm, consistent with π–π* transitions from sp² carbon domains and n–π* transitions associated with surface carbonyl groups. Under 450 nm excitation, the CQDs exhibit bright green fluorescence with an emission maximum at 509 nm. The photoluminescence also displays excitation-dependent red shifting, suggesting emission contributions from surface states and nanoscale structural heterogeneity. Fluorescence microscopy of the deposited CQDs reveals spatially random emission patterns and aggregation morphologies, indicating strong promise for optical PUF generation. Preliminary image analysis further suggests that unique binary identifiers can be extracted from local fluorescence features, supporting the feasibility of CQD-based optical fingerprinting. These results demonstrate that waste-derived CQDs are promising low-cost, sustainable candidates for secure optical tagging and anti-counterfeiting technologies. Future work will focus on full fingerprint generation and quantitative evaluation of key PUF metrics, including randomness, uniqueness, conciseness, storage capacity, and stability, to assess device robustness and application potential.