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. 2022 Oct 8;12:16919. doi: 10.1038/s41598-022-20596-8

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© The Author(s) 2022

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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The concept of using the non-linear response of a quantum dot-based tag for authentication. (a) Illustrates a security tag’s surface, coated in quantum dots and divided into pixels for clarity. As the incident illumination increases (from left to right at 3 excitation powers, E1, E2, E3) the average amount of photoluminescence (shown in red) increases, but at different rates from region to region. T1, T2 and T3 show the switch-on intensities of different QD regions. (b) Sketches how the photoluminescence intensity from three example locations could vary differently with increasing excitation. (c)–(f) The top section of each panel shows photoluminescence from a thin film containing colloidal quantum dots at increasing excitation power, with pixel histograms underneath displaying the number of pixels recording each intensity value (0 to 65,355) at the different incident powers: 36.4 μW (c), 57.6 μW (d), 91.4 μW (e), and 145 μW (f). Scale bar represents 50 μm.