Abstract
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.
Highlights
Lanthanide-activated phosphors are famous as powerful multicolor-emitting materials due to the fact that the abundant ladder-like energy levels enable even single trivalent lanthanide ion to provide multiple emissions with various wavelengths in the visible region [1]
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
A pumping-controlled dual-mode anti-counterfeiting strategy is conceived by taking advantage of the combination of up-conversion processes with different photon numbers
Summary
Lanthanide-activated phosphors are famous as powerful multicolor-emitting materials due to the fact that the abundant ladder-like energy levels enable even single trivalent lanthanide ion to provide multiple emissions with various wavelengths in the visible region [1]. Lanthanide up-conversion features stepwise multiphoton 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 These important characteristics have been recently utilized for the color tuning of up-conversion emission, represented either by excitation power density dependent multi-color emission or pulse-width modulated control over the emission color [14,15,16,17]. The life-time decay curves for the correspond emissions of both the Er3+ and Tm3+ ions in the core/triple-shell nano-crystals (NCs) exhibited distinctly diverse rising edge, which leads to a bright multicolor trajectory when a designed pattern made of such core/triple-shell NCs is rotated These two pumpingrelated phenomena can be integrated for a dual-mode anti-counterfeiting design
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