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

Abstract

Lanthanide up-conversion features stepwise multi-photon processes, where the difference in photon number that is required for specific up-conversion process usually leads to significant variance in pumping-related processes/properties. In this work, a pumping-controlled dual-mode anti-counterfeiting strategy is conceived by taking advantage of the combination of up-conversion processes with different photon numbers. The combination of Er3+ and Tm3+, which are spatially separated within a designed core/triple-shell nano-architecture, is taken as an example to illustrate such idea. Upon infrared excitation, the emission color of a designed pattern can be switched from red to purple by increasing the excitation power density from 5 to 11 W/cm2, while a bright luminescent trajectory including red, white and blue-green color with different length is observed when rotating the pattern above 600 rpm. In addition, the relative up-conversion emission intensities of the Er3+ and Tm3+ ions can be manipulated through tailoring interfacial or inner defects in the core/triple-shell nano-crystals, which enable an ultrahigh sensitivity for the pumping-controlled emission color variation to be observed under excitation power well below 11 W/cm2.

Luminescence anti‐counterfeiting: From elementary to advanced

“…In addition to excitation light, luminescence lifetime, heat stimuli, and chemical regents, many other regulation factors, such as rotation speed and mechanical stimuli have been also explored to regulate the luminescence of anti‐counterfeiting label. [ 106,121 ] For example, Dai et al. [ 106 ] utilized NaErF 4 :10Yb@NaYF 4 @NaYbF 4 :20Ca/1Tm@NaYF 4 nanocrystals (NCs) to stamp an anti‐counterfeiting pattern whose luminescence was closely associated with rotation speed and excitation power (Figure 8A).…”

“…[ 106,121 ] For example, Dai et al. [ 106 ] utilized NaErF 4 :10Yb@NaYF 4 @NaYbF 4 :20Ca/1Tm@NaYF 4 nanocrystals (NCs) to stamp an anti‐counterfeiting pattern whose luminescence was closely associated with rotation speed and excitation power (Figure 8A). As excitation power was increased from 5 to 11 W cm −2 , the emission color of anti‐counterfeiting pattern gradually changed from red to purple due to the excitation power‐dependent luminescence characteristics of such materials.…”

“…Reproduced with permission: Copyright 2020, De Gruyter. [ 106 ] (B) Co‐regulated by mechanical stimuli, UV light, and luminescence lifetime. Reproduced with permission: Copyright 2019, Royal Society of Chemistry.…”

“…Based on the category of regulation factors, multilevel luminescence anti‐counterfeiting can be divided into five types: (1) regulated by excitation light; [ 64–80 ] (2) co‐regulated by excitation light and luminescence lifetime; [ 81–92 ] (3) co‐regulated by excitation light and heat stimuli; [ 35,63,93–96 ] (4) co‐regulated by excitation light and chemical reagents; [ 16,97–105 ] and (5) co‐regulated by other factors. [ 106–121 ]…”

Ce3+/Tb3+‐coactived NaMgBO3 phosphors toward versatile applications in white LED, FED, and optical anti‐counterfeiting

“…29 Consequently, rare-earth-activated phosphors with multi-mode emissions and high stability are treated as a promising candidate for optical anti-counterfeiting. 30 As a part of rare-earth ions, Tb 3+ ions are usually used as green activators in luminescent materials since its dominated emission from the 5 D 4 → 7 F 5 transition. 31 However, the parity-forbidden 4f−4f transitions result in narrow and weak excitation peaks in NUV region, leading to the limited applications of the Tb 3+ -activated green phosphors.…”