Nanocomposites and nanomaterials
Infrared emitting nanoparticles with variable luminescence lifetimes for anti-counterfeiting and security applications
Ziniuk R.1, Yakovliev A.1, Qu J.1, Ohulchanskyy T.Y.1
1Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen, Guangdong Province, 518060, P. R. China
E-mail: romanziniuk.94@hotmail.com

The forgery and counterfeiting of all kinds of official documents have been becoming a real threat to the society. Recently, rare-earth ion doped nanoparticles (RENPs) have been widely used for anti-counterfeiting and security applications due to their unique optical properties [1]. In particular, the photoluminescence (PL) characteristics (i.e., spectral position and shape, PL lifetime, etc.) can be tuned and optimized during RENPs synthesis and further controlled by PL excitation parameters [2]. Modern nanochemistry technique allows for synthesis of RENPs with emission tuned to near- and shortwave-infrared (NIR-SWIR) spectral range, which is beneficial for luminescence imaging through various materials (including biological tissues) due to the reduced scattering of infrared light in comparison with visible one [3]. Time-resolved PL imaging in NIR-SWIR spectral range can help to distinguish and map area with different PL features in anti-counterfeiting and security applications. In this work, the PL temporal coding approach using Yb3+/Er3+-doped nanoparticles is reported. PL lifetimes from Yb3+ and Er3+ ions are shown to be tunable with the doping concentration and excitation parameters. A combination of time-resolved PL imaging with lifetime unmixing algorithms demonstrates the applicability of RENPs for NIR-SWIR PL multiplex imaging in anti-counterfeiting and security applications.

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[2]	Y. Wang, K. Zheng, S. Song, D. Fan, H. Zhang, and X. Liu, ‘Remote manipulation of upconversion luminescence’, Chem. Soc. Rev., vol. 47, no. 17, pp. 6473–6485, Aug. 2018, doi: 10.1039/C8CS00124C.
[3]	S. Ding, L. Lu, Y. Fan, and F. Zhang, ‘Recent progress in NIR-II emitting lanthanide-based nanoparticles and their biological applications’, Journal of Rare Earths, Mar. 2020, doi: 10.1016/j.jre.2020.01.021.