Mechanoluminescence. (L-R) light from loose N-acetylanthranilic acid crystals crushed between transparent windows; light from similar crystals shaped into a logo, then crushed between two windows. [Image: Photonics, courtesy of Nathan C. Eddingsaas & Kenneth S. Suslick]
Way back in 1605,Â English philosopher, statesman, and scientist Francis Bacon first demonstrated the phenomenon of mechanoluminescence â€“Â light emission resulting from a mechanical action on a solid â€“ by breaking apart sugar crystals. Since that time, researchers around the world have worked to develop mechanoluminescent (ML) materials, and the main ones studied include zinc sulphide, molecular crystals, quartz, and alkali halides. This principle can be produced through an ultrasound, along with some other processesâ€¦such as 3D printing.
Mechanoluminescence is the center of the latest 3D printing research from the Hebrew University of Jerusalem, partially supported by the Singapore National Research Foundation under the CREATE (Campus for Research Excellence and Technological Enterprise) program.
A team of researchers from the universityâ€™sÂ
The abstract reads, â€œWe report on new material compositions enabling fully printed mechanoluminescent 3D devices by using a one-step direct write 3D printing technology. The ink is composed of PDMS, transition metal ion-doped ZnS particles, and a platinum curing retarder that enables a long open time for the printing process. 3D printed mechanoluminescent multi-material objects with complex structures were fabricated, in which light emission results from stretching or wind blowing. The multi-material printing yielded anisotropic light emission upon compression from different directions, enabling its use as a directional strain and pressure sensor. The mechanoluminescent light emission peak was tailored to match that of a perovskite material, and therefore, enabled the direct conversion of wind power in the dark into electricity, by linking the printed device to perovskite-based solar cells.â€�
Top: Schematic of energy harvesting in the dark using a wind-driven ML device and a perovskite-based solar cell; Bottom: Anisotropic mechanoluminescent (AML) device. Photo of an AML device on (a) horizontal compression and release from the sides (I,Â red arrows), (b) schematic of an AML device, and (c) diagonal compression and release (II, blue arrows). The scale bar is 10 mm.
When mechanically stretched, the 3D printed ML objects will emit light. According to the researchers, the color of this light can be tailored â€œaccording to the chemical composition of particles embedded within the 3D object.â€�
The 3D printed polymeric objects will also emit light when they move slightly after being exposed to air flow that mimics wind; by linking the object to a solar cell, this light can actually be converted into electricity, so solar cells could one day harvest precious wind energy in the dark. Potential applications for 3D printed ML materials includeÂ security inks, flexible and embedded directional sensors, dynamic mapping of personal signatures, and using wind energy to generate light.
Dr. Patel 3D printed the ML devices based on a new process, and materials compositions that allow for the 3D printing of multi-material objects with complex structures. This process is based on direct ink writing (DIW) technology, and was able to successfully 3D print ML materials embedded within elastomeric monomers. The team used multi-material 3D printing to pattern ML objects withÂ multiple color emission; these objects can then be used to generateÂ anisotropic light emission which is used as a directional sensor.
(a) Printing of ML device; (b) 3D printed ML candy (inset is photo of green light-emitting candy under UV exposure); (c) luminescence spectrum generated from ML candy; (d) photo of ML candy under compression and release; (e) 3D printed ML objects; (f) ML spectra under continuous stretching and release.
The research team also 3D printed wind-driven ML devices in just one step, and later combined them with perovskite-based solar cells, developed by El Cohen in Professor Etgarâ€™s group, in order to directly convert wind energy into electricity in the dark. These solar cells enabled a higher power generation than any previously reported, byÂ tailoring the absorbing material inside the solar cells to the 3D printed ML deviceâ€™s specific light emission.
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[Images: Magdassi et al]