Multistimuli‐Responsive Display Materials to Encrypt Differentiated Information in Bright and Dark Fields

Abstract

Visually readable codes play a crucial role in anticounterfeiting measures. However, current coding approaches do not enable time-dependent codes to be visually read, adjusted, and differentiated in bright and dark fields. Here, using a combined strategy of piezoelectric lattice selection, oxygen vacancy engineering, and activator doping, a lanthanide ion-doped titanate is developed that integrates mechano-, thermo-, and photo-responsive color change (>18 h for bright field), persistent luminescence (>6 h for dark field), and stimulus-triggered multimodal luminescence. The feasibility of optical encoding, visual displaying, and stimulus-responsive encrypting of timedependent, dual-field information by using the developed material is demonstrated. In particular, the differentiated display of dual-field modes is achieved by combining mechanostimulated abolition of only the persistent luminescence and thermo-and photostimulated reversal of both the color change and persistent luminescence. The results provide new insights for designing advanced materials and encryption technologies for photonic displays, information security, and intelligent anticounterfeiting.

Short-Term Non-Decaying Mechanoluminescence in Li2MgGeO4:Mn2+

“…The most attractive ML feature of Li2MgGeO4:Mn 2+ is its short-term non-decaying ML behavior, which is quite distinct from the reported trap-controlled reproducible ML materials characterized by the decaying behavior of ML [14,15,18,21,23,[26][27][28][29]. During an experiment using continuous rod friction (4π rad/s) at different pressures, the ML signal showed a nearly stable periodic oscillation during ~20 cycles (Figure 4a).…”

“…For example, NaNbO 3 :Pr 3+ [14], La 1.95 Ti 2 O 7 :Pr 3+ [15], and Ca 3 Ti 2 O 7 :Pr 3+ [29] only have ThL peaks below 150 • C (corresponding to shallow traps), while there are no high-temperature ThL peaks (corresponding to deep traps, such as the 150-250 • C ThL peak in Li 2 MgGeO 4 :Mn 2+ ). On the other hand, all of these materials show a typical decaying behavior even under short-term cyclic frictional stimuli [14,15,29]. Therefore, we reasonably ascribed their continuous decaying behavior to the gradual emptying of shallow traps and the absence of carrier replenishment from deep traps.…”

“…Therefore, we reasonably ascribed their continuous decaying behavior to the gradual emptying of shallow traps and the absence of carrier replenishment from deep traps. [14], La1.95Ti2O7:Pr 3+ [15], and Ca3Ti2O7:Pr 3+ [29] only have ThL peaks below 150 °C (corresponding to shallow traps), while there are no high-temperature ThL peaks (corresponding to deep traps, such as the 150-250 °C ThL peak in Li2MgGeO4:Mn 2+ ). On the other hand, all of these materials show a typical decaying behavior even under short-term cyclic frictional stimuli [14,15,29].…”

“…Mechanoluminescent (ML) materials that can quantitatively convert mechanical stimuli into light emission have drawn great attention due to potential applications ranging from stress distribution visualization [1,2] and structural health diagnosis [3][4][5] to light sources [6][7][8][9][10][11][12][13] and anti-counterfeiting [14][15][16]. Dozens of inorganic ML materials with reproducible mechanoluminescence (ML) have been developed during the past two decades [17,18].…”

“…Another type that requires irradiation is trap-controlled ML materials [18]. Most developed reproducible ML materials are of this type, such as SrAl 2 O 4 :Eu 2+ ,Dy 3+ [21], CaYAl 3 O 7 :Ce 3+ [22], BaSi 2 O 2 N 2 :Eu 2+ [23], Sr 3 Sn 2 O 7 :Sm 3+ [24], and LiNbO 3 :Pr 3+ [25], as well as CaZr(PO 4 ) 2 :Eu 2+ [26], (Ca,Sr) 2 Nb 2 O 7 :Pr 3+ [27,28], Ca 3 Ti 2 O 7 :Pr 3+ [29], NaNbO 3 :Pr 3+ ,Er 3+ [14], and La 1.95 Ti 2 O 7 :Pr 3+ [15], developed by our lab. These materials employ carrier traps to store excitation energy from light irradiation (e.g., ultraviolet (UV) excitation).…”