Electro‐Photoluminescence Color Change for Deformable Visual Encryption

Abstract

In order to utilize the concept of the radiation-responsive luminous color change and develop further for practical uses, electroluminous system can be a good platform because the light intensity can be controlled. Surprisingly, the radiation-responsive electroluminous color change has not been investigated so far. The reason is, in general, the variation range of the wavelength emitted by the external radiation is narrow. [30][31][32][33] For the electroluminous color change triggered by radiation, the luminophore used in the electroluminescence (EL) must have strong photoluminescence (PL) and the PL wavelength must have a large difference from the EL wavelength. In addition, the PL and EL are desirable to be controlled independently so that the resulting color change is predictably tunable. In this study, we present, for the first time, a UV-responsive electroluminous color changing system, called electrophotoluminescence (EPL) color change. As a model system, we used the stretchable alternating current electroluminescence (ACEL) in which the electro-luminophores are photoluminescent as well. We investigated systematically the effects of the ACEL frequency and voltage to obtain a wide range of color variation. We utilized the EPL color changing system to demon strate a deformable visual encryption on the skin of a soft robotic rover.Even though this study focuses on controlling the EPL colors and understanding the physical origins, the device fabrication required material advances in several aspects. The device structure is illustrated in Figure 1b (top) and the cross-sectional scanning electron microscopy (SEM) image is presented in Figure 1c. A light-emitting layer (150 µm in thickness) was sandwiched between two stretchable electrodes. A hydrogel ionic conductor or indium-tin oxide (ITO) was used as the top electrode to ensure high transparency in the UV-vis range ( Figure S1, Supporting Information). In order to ensure adhesion of the hydrogel ionic conductor and the light-emitting layer under deformation, surface of the light-emitting layer was treated with benzophenone. The benzophenone treatment increased the turbidity and modulus of the polymer matrix (Ecoflex 00-30) in the light-emitting layer. Therefore, the benzophenone treatment for 10 min was chosen as an optimum condition for achieving enough adhesion without large increase of turbidity and modulus. The dependence of the modulus and transmittance on the benzophenone treatment time is shown in the Figure S2, Supporting Information.Although structural coloring and photoluminescence (PL) have been investigated for radiation-responsive color change, electroluminescence (EL) has not been used for the radiation-responsive system. An electrophotoluminescence (EPL) color change is presented here. The phosphors in the alternating current electroluminescence (ACEL) act simultaneously as electro-luminophores and photo-luminophores. The EPL chromaticity is systematically investigated depending on the ACEL frequency and UV intensity. It is found that the PL va...

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Interface Design for Stretchable Electronic Devices

“…[40] The stretchable patterned electrode wrapping the nerve fibers has been used for electrical stimulation and also for signal detection in the brain. [41] A usual approach of manufacturing a stretchable device is to assemble an intrinsically stretchable active layer on a stretchable electrode, [42,43] then interconnect the active unit to other device units through a stretchable conducting line. [44,45] In this approach, all the device components are stretchable.…”

“…A usual approach of manufacturing a stretchable device is to assemble an intrinsically stretchable active layer on a stretchable electrode, [ 42,43 ] then interconnect the active unit to other device units through a stretchable conducting line. [ 44,45 ] In this approach, all the device components are stretchable.…”

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