Anti-counterfeiting strategy based on multiwavelength photothermal particles to disclose thermal imaging

Abstract

Product counterfeiting is a major problem worldwide, not only because of the economic losses but also because of the negative impact it has on society. Therefore, it becomes a constant need to propose advanced anti-counterfeiting methods or technologies which, ideally, should be non-cloneable, easy to implement, difficult to remove-reuse, and versatile. Although numerous systems already exist on the market or in the literature, some of them lack of the above specifications, which complicates their actual implementation. In this contribution, an easy-to-print, safe and non-restrictive anti-counterfeiting system based on the generation of thermal images by the photothermal effect of LaBO3:Ln3+ particles is proposed. Wavelength excitation, 808 or 975 nm, for photothermal effect can be tuned by selecting properly the lanthanide ion (Nd or Yb). The temperature generated by the synthesized samples covers a range from 25 to 300 °C approximately, when excited with the appropriate infrared laser diode (LD) at powers from 0.015 to 2.1 W. Using a simple screen-printing method, codes were printed using the LaBO3:Nd3+ and LaBO3:Yb3+ particles, which allow the generation of simple or complex thermal images under appropriate infrared laser radiation. The combination of the two synthesized materials allows the generation of codes whose decoding is subject to a specific sequence dependent on the excitation wavelengths. As a proof of concept, the generated codes are printed on various drug packaging, as well as on banknotes and business cards. Printing versatility and the security level generated by the sequence of multiple excitation wavelengths of thermal and visible codes allow the proposed system to be used in printed security applications.