Dynamic Control of Orthogonal Upconversion in Migratory Core–Shell Nanostructure toward Information Security

Abstract

Lanthanide-based materials exhibit abundant emission colors under suitable infrared excitations; however, the dynamic control of orthogonal photon upconversion of lanthanide ions has remained challenging. Here, a novel mechanistic strategy to enable orthogonal upconversion emissions through energy migration in a simple core-shell nanostructure is reported. By constructing the migratory ytterbium-sublattice shell layer outside the luminescent erbium matrix, the population of erbium emitters at their intermediate energy levels can be finely manipulated, and the red-to-green color-switchable output has been achieved under separate 980 and 808 (or 1530) nm excitations. More interestingly, a tuning of the excitation pulse width also results in a gradual red-to-green color change. The mechanistic role of energy migration over ytterbium sublattice is also examined. A conceptual core-shell model for the excitation-emission orthogonal upconversion output is provided, which is not only important for the fundamental research of photon upconversion but also helps in exciting new chances for the frontier applications such as information security.

Controlling upconversion in emerging multilayer core–shell nanostructures: from fundamentals to frontier applications

“…We further optimized this core-shell structure and also achieved the red-green orthogonal upconversion with 980/808 nm dual-excitation in NaErF 4 :Yb/Tm@NaYbF 4 core-shell UCNPs. 149 Moreover, this structure shows a temporal response characteristic, and the red-green orthogonal upconversion was also realized under non-steady-state excitation. 149 When the 980 nm laser duration is reduced from continuous wavelength (c.w.)…”

“…149 Moreover, this structure shows a temporal response characteristic, and the red-green orthogonal upconversion was also realized under non-steady-state excitation. 149 When the 980 nm laser duration is reduced from continuous wavelength (c.w.) to the pulse of 50 ms, the green emission is gradually increased in contrast to the red emission of Er 3+ (Fig.…”

“…68,69,147,148 By rational designs of the MLCS materials consisting of different emission components, their emission colours can be smartly modulated by adopting a suitable external excitation source, e.g., excitation wavelengths, power density, and use of pulse excitation. 61,65,148,149 This provides a powerful nanoplatform for a switchable multicolour output with great promise in frontier applications including advanced multiple anticounterfeiting, 61,150,151 information security, 137,149 multicolour display, 58,135 photo-switching, 147,152 spectral and life-time encoding, 153,154 rewritable optical memory, 59 super-resolution nanoscopy, 155 bioimaging-guided therapeutics, 156,157 and neuronal manipulation. 158…”

“…9c). 58,149,163 This route is much important to realize the aim in the MLCS nanostructure but does not increase its complexity. Therefore, the present synthetic methods are enough to obtain these nanostructures experimentally.…”

“…11e). 149 These studies provide a new perspective for more convenient and versatile modulation methods to simplify the MLCS system by material synthetic design in addition to the optimization of the MLCS nanostructure and external conditions.…”