Achieving Thermo‐Mechano‐Opto‐Responsive Bitemporal Colorful Luminescence via Multiplexing of Dual Lanthanides in Piezoelectric Particles and its Multidimensional Anticounterfeiting

Abstract

copy and easy to authenticate) is the primary approach for resisting the increasing sophistication of counterfeiting. [1] Due to their visual identifiability, colorful light emissions of luminophors are considered to be ideal security elements. The luminescent patterns of banknotes under ultraviolet (UV) excitation are a well-known sample of this approach. In addition to the spatial spectral fingerprints displayed in emission colors, the excitation mode and emission lifetime of luminescence can be used as authentication information, providing higher coding levels. For example, photoluminescence (PL), upconversion luminescence (UCL), and long-lasting luminescence (LLL) are three quintessential modes for anticounterfeiting and information security. [2] The PL mode produces photons at longer wavelengths than the excitation wavelength, for example, downshifting UV excitation to visible emission. [3] The UCL mode converts longwavelength photons to short-wavelength ones, for example, in the upconversion of near-infrared (NIR) excitation to visible emission. [4] It is important to note that PL and UCL phenomena will disappear immediately once light excitation is stopped, showing a feature of pulse duration (so-called fluorescence). In contrast, LLL shows delayed initiation after the cessation of Optical characteristics of luminescent materials, including emission color (wavelength), lifetime, and excitation mode, play crucial roles in data communication and information security. Conventional luminescent materials generally display unicolor, unitemporal, and unimodal (occasionally bimodal) emission, resulting in low-level readout and decoding. The development of multicolor, multitemporal, and multimodal luminescence in a single material has long been considered to be a significant challenge. In this study, for the first time, the superior integration of colorful (red-orange-yellowgreen), bitemporal (fluorescent and delayed), and four-modal (thermo-/ mechano-motivated and upconverted/downshifted) emissions in a particular piezoelectric particle via optical multiplexing of dual-lanthanide dopants is demonstrated. The as-prepared versatile NaNbO 3 :Pr 3+ ,Er 3+ luminescent microparticles shown are particularly suitable for embedding into polymer films to achieve waterproof, flexible/wearable and highly stretchable features, and synchronously to provide multidimensional codes that can be visually read-out using simple and commonly available tools (including the LED of a smartphone, pen writing, cooling-heating stimuli, and ultraviolet/ near-infrared lamps). These findings offer unique insight for designing highly integrated stimuli-responsive luminophors and smart devices toward a wide variety of applications, particularly advanced anticounterfeiting technology.

Ferroelectric domains and luminescent properties of Pr3+‐doped Ca2Nb2O7 ceramics

“…On the other hand, inorganic photoluminescence (PL) materials doped with rare‐earth (RE) ions have found broad applications in optical anti‐counterfeiting, information storage and other fields for their excellent luminescence and environmental tolerance . Compared to PL, which directly absorbs photon energy and emits light during light excitation, thermoluminescence (TL) is generally considered to be related to the point defects and includes a detrapping process of charge carriers under thermal stimuli .…”

Multiple‐response anti‐counterfeiting realized in CaYAl3O7 host with the dual coexistence of Eu2+/Eu3+

“…Herein, phosphors with photoluminescence (PL), up‐conversion luminescence (UCL), photo‐stimulated luminescence (PSL), mechano‐luminescence (ML), thermoluminescence (ThL) and long persistent luminescence (LPL) have been developed to realize anti‐counterfeiting features against counterfeiters to replicate. Nevertheless, monofunctional characteristics with unicolor emission output by utilizing certain substitutes or simply mixing different fluorescent materials, exhibit unsatisfied anti‐counterfeiting performance . Therefore, the increasing demands for optical anti‐counterfeiting technology require the development of versatile luminescent materials with multiple models and tunable photoluminescence.…”

“…Nevertheless, monofunctional characteristics with unicolor emission output by utilizing certain substitutes or simply mixing different fluorescent materials, exhibit unsatisfied anti-counterfeiting performance. [11][12][13][14] Therefore, the increasing demands for optical anti-counterfeiting technology require the development of versatile luminescent materials with multiple models and tunable photoluminescence. The detected optical signal is recorded to identify the source information after being irradiated, which performs high concealment properties.…”

Ultrasensitive and Recyclable Upconversion‐Fluorescence Fibrous Indicator Paper with Plasmonic Nanostructures for Single Droplet Detection

“…Similarly, a traditional particulate-based fluorescence sensor is also not reusable because it usually suspends fluorescent nanoparticles such as quantum dots and upconversion nanocrystals in the target solution to initiate detection, [6][7][8][9] which are often unstable and irreproducible when contaminated by the target solution. [12,13] Moreover, fluorophores with stronger fluorescence can suppress background noise and autofluorescence, bringing about more sensitive detection. On the other hand, the sensitivities of current fluorescence indicator paper and sensors are still expected to improve because a higher sensitivity can respond to target solutions with a lower concentration, which will benefit the application of trace detection.…”

“…[12,13] Moreover, fluorophores with stronger fluorescence can suppress background noise and autofluorescence, bringing about more sensitive detection. [12,13] Moreover, fluorophores with stronger fluorescence can suppress background noise and autofluorescence, bringing about more sensitive detection.…”