Tunable Emissions of Upconversion Fluorescence for Security Applications

Abstract

The rampant appearance of counterfeiting has a serious adverse effect on every aspect in the global markets. Thus, the development of high‐tech security strategies has become an urgent challenge. Recently, lanthanide ions (Ln3+) doped materials open new avenues for concealing factual data and shield against counterfeiting because of their unique optical characteristics of color‐tunable emissions under near‐infrared excitation. The present review surveys the recent advances in Ln3+‐doped upconversion crystals (UCCs) as fluorescent functional inks toward designable and high‐level anti‐counterfeiting patterns and graphical encoding. The great achievements of fabrication of versatile security patterns can be ascribed to the combination of the single or multiple colorful UCCs with polymers, additives, and solvents. Moreover, the crucial factors including underlying mechanisms, synthetic methods of upconversion fluorescence materials, and the diverse printing technologies employed for patterning the fluorescence images have been highlighted, and the corresponding challenges and opportunities in this promising research area are presented. This review will help providing a fundamental understanding and guidance to rational design fluorescence optical labels based on Ln3+‐doped UCCs for broadening their applications in high‐level security fields.

Direct Photolithographic Deposition of Color‐Coded Anti‐Counterfeit Patterns with Titania Encapsulated Upconverting Nanoparticles

“…This type of optical multi-plexing can be achieved by tuning the emission lifetimes of the UCNPs by synthetic methods through a core-shell-shell design, metal ion doping, or through adjusting the relative concentrations of the lanthanide species. [26,83,84] Future studies may also include further packaging of the metal oxide films with a thin, transparent polymer layer to prevent consumer contact with the UCNPs. These particles remained adhered to the titania films while processing these patterns, but additional measures could be necessary to ensure consumer safety.…”

“…Patterning of upconversion materials on these substrates enables multi-plexing of the optical signals for use in anti-counterfeiting applications. [26] The upconversion materials can be formulated to produce the desired color of emission only at specific excitation power densities. [20,27,28] The distinct luminescence lifetimes of UCNPs also make them even more difficult to replicate.…”

Pumping-controlled multicolor modulation of upconversion emission for dual-mode dynamic anti-counterfeiting

“…Up to now, several methods, including manipulating nearfield effects (i. e., electronic, magnetic, and plasmon field) [2][3][4][5][6][7], environmental temperature or excitation conditions (i. e., excitation wavelength/pulse width/power density) [8][9][10][11], have been applied to realize the control of emission color change. These offer a powerful platform for the design of multi-mode anti-counterfeiting techniques, where two or more various stimulation-induced emission color change effects can be judiciously integrated into single luminescence material so as to greatly outperform the single-mode techniques in terms of security capability [12,13].…”

Thermal-responsive multicolor emission of single NaGdF4:Yb/Ce/Ho upconversion nanocrystals for anticounterfeiting application

“…have seriously threaten the health of consumer, the interest of enterprise, and the financial security of society. Anticounterfeiting strategies can make the genuine product difficult to be replicated and effectively impede fraudulent goods from being traded in a market [2,3]. As one of security strategies, lanthanidedoped upconversion nanocrystals (UCNCs) have advantages of a low background fluorescence and a strong resistance to photobleaching.…”