Dual Stimuli-Responsive Inks Based on Orthogonal Upconversion Three-Primary-Color Luminescence for Advanced Anticounterfeiting Applications

Abstract

Stimuli-responsive fluorescent materials have recently been developed and employed as fluorescent security inks for applications in the fields of high-level security protection and multi-anticounterfeiting because they can provide extra security features by switching luminescence outputs in response to external stimuli. However, conventional stimuli-responsive fluorescent inks are generally limited to unicolor or dual-color fluorescent response behaviors in monotonous stimuli mode, resulting in being comparatively less effective for advanced anticounterfeiting applications. Herein, we report a new strategy for constructing a dual stimuli-responsive multicolor security ink, which is based on the integration of the near-infrared (NIR) light-responsive orthogonal three-primary-color luminescence properties of upconversion nanoparticles and pH-sensitive color-changing behavior of thymolphthalein dye. Unlike most other invisible security inks, this new dual stimuli-responsive security ink can realize visualization of hidden information. The information recorded by this ink is initially visible under natural light and then spontaneously becomes invisible within several tens of seconds. The feature of disappearance in seconds allows customers to check and correct concealed information before hiding it. In addition, upon pH stimulation, the concealed information can be reversibly interconverted between visible and invisible states. Meanwhile, upon ternary NIR quadrature excitation (808/980/1560 nm), the information can emit intense green, blue, and red fluorescence, respectively. More importantly, the information printed with the security ink exhibits robust stability against various chemical treatments, which demonstrates great potential for practical applications in advanced anticounterfeiting.

Dual-Color Photoluminescent Functionalized Nanoparticles for Static-Dynamic Anticounterfeiting and Encryption: First Collaboration of Spiropyran and Coumarin

“…For example, Jia and co-workers developed a new category of anticounterfeiting materials based on orthogonal upconversion of three primarycolor luminescence nanoparticles with multi-responsivity toward pH and various wavelengths of light irradiation. 13 The printed security tags displayed color change from the invisible state to the visible blue state by the increase of pH to above 10.5, and also, the printed invisible security tags emitted green, blue, and orange emissions upon excitation with NIR laser with wavelengths of 808, 980, and 1560 nm, respectively. A significant challenge in such advanced anticounterfeiting systems is the higher cost of raw materials and also special instruments such as laser light sources, which are not available at any time and place.…”

Supramolecular Polymers with Photoswitchable Multistate Fluorescence for Anti-Counterfeiting and Encryption

“…In recent years, stimuli-responsive fluorescent materials (SFMs), whose luminescence is sensitive to environmental stimuli, have a wide range of applications in the fields of biosensors, bioimaging, anti-counterfeiting, information encryption, etc. − SFMs with various stimuli, including light, temperature, pressure, ion, acid–base, and humidity, have been studied. − Compared with other types of SFMs, photoswitchable fluorescent systems with the phototrigger mechanism display the desired properties, including remote control, waste-free, noninvasive, high spatial, and temporal resolution. − …”

NaYF4:Yb,Er@NaYF4:Yb,Tm and NaYF4:Yb,Tm@NaYF4:Yb,Er Core@Shell Upconversion Nanoparticles Embedded in Acrylamide Hydrogels for Anti-Counterfeiting and Information Encryption

“…Among them, temperature-sensitive luminescent materials require harsh temperature conditions to achieve luminescence transformation, which generally needs to be below −100 °C or above 100 °C, with low sensitivity and limited application scenarios. 31−33 pH-sensitive luminescent materials need the use of acid-based reagents, 34,35 which is not practical for consumers who do not have chemical knowledge to add acids, bases, or other chemicals on the label.…”

“…The second is continuous illumination decoding and encryption of luminescent materials, but the process of encryption and decoding is obviously time-consuming. , The third type constitutes stimulus-responsive luminescent materials, mainly temperature-sensitive and pH-responsive materials. Among them, temperature-sensitive luminescent materials require harsh temperature conditions to achieve luminescence transformation, which generally needs to be below −100 °C or above 100 °C, with low sensitivity and limited application scenarios. − pH-sensitive luminescent materials need the use of acid-based reagents, , which is not practical for consumers who do not have chemical knowledge to add acids, bases, or other chemicals on the label.…”