Magnetic‐Force‐Induced‐Luminescent Effect in Flexible ZnS:Cu/PDMS/NdFeB Composite

Abstract

The polydimethylsiloxane (PDMS)supported composite structure has gained attention due to its durability, easy fabrication, mechanical robustness, and low cost, and these features allow the development of flexible devices with capabilities in sensing and actuation. [4] Recently, Miao et al. developed magnetic-controlled 3D robotic structures based on neodymium iron boron (NdFeB) microparticles and PDMS at different scales and locomotion. [5] Mechanoluminescence (ML) is considered as a luminescence phenomenon in solids induced by mechanical stress, as first introduced in 1605. [6] Wang's group suggested piezo-photonic effect, which could be regarded as piezoelectricity and photoexcitation coupling effect. [7] ML, also named as piezoluminescence (PL), is regarded as a promising energy conversion mechanism; it refers to light emission induced by mechanical actions such as stretching and compressing on a solid. It has been of much interest due to energy-saving nature in a wide range of applications such as health-monitoring sensors, bioimaging, stress field visualization, artificial skin, electroluminescence devices, light emitting displays, and optical sensors. [8] Phosphor-based luminescent materials are currently the main stream of light-emitting materials because of their semiconductor behavior with a wide energy bandgap. Phosphorbased semiconductor is also capable of hosting different metal ion dopants as luminescent center. Meanwhile, a typical, The force-induced light-emitting phenomenon in polymer composites plays an important role in the soft electronic field due to its display function. Here, a magnetic-force-induced-luminescence (MFIL) effect is reported in ZnS:Cu particle-doped polydimethylsiloxane incorporated with a NdFeB magnetic tip mass for real-time incident magnetic field strength light-emitting display. Investigations show that the luminescence intensity increases nearly linear in response to the applied AC magnetic field, H AC ; meanwhile, the minimum H AC for inducing MFIL is as low as 0.1 mT (1 Oe) at the resonance. The MFIL effect is 1000 times better and more energy-efficient than the best result published previously. The findings, thus, indicate that the MFIL effect could serve as an effective method for light-emitting display triggered by H AC ; MFIL essentially originates from the donor-acceptor recombination between shallow donor level and the t 2 level of Cu 2 in ZnS:Cu semiconductor particles. The present results could, thus, provide a viable pathway toward multifunctional flexible electronic designs and applications, especially toward those for the real-time visualization of remote magnetic field sensing.

Revealing the Intrinsic Decay of Mechanoluminescence for Achieving Ultrafast‐Response Stress Sensing

“…[34] For ML, the rise and decay of intensity over time is not only the basis for understanding the mechanoto-photon conversion mechanism but also the key to determine the time-domain responsiveness in high-frequency sensing applications. [35][36][37] Different from the transient resonance absorption of incident photons in photoluminescence (PL), the absorption of mechanical energy in ML depends on both the duration of input mechanical actions and the deformation of ML materials. In this regard, a low loading rate (e.g., that provided by a universal tester) or slow deformation relaxation (e.g., from an elastomer matrix) as used in previous studies would result in an excessively long excitation duration, [38,39] which eventually submerges the intrinsic intensity variation of ML.…”