A material that lights up when stretched or placed under UV light could make bank notes harder to counterfeit.
Mechanoluminescent materials light up when they鈥檙e rubbed, bent, or stretched. Songshen Zeng at the University of Connecticut and his colleagues have made a new one using rare earth elements.
When a rubbery strip of it is stretched, charged particles within its molecular structure gain energy and are jostled out of their places. As they settle back in, they release that extra energy in the form of light.
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鈥淚n our material, we have stronger and brighter luminescence compared to more traditional mechanoluminescent materials,鈥� says Zeng. It鈥檚 also more environmentally friendly, he says, because the traditional materials often release toxic compounds as they degrade.
Hidden message
By embedding a pattern made of this glowing material into rubber, the team could create hidden messages that were only revealed by applying strain.
For an added layer of security, the researchers combined their material with one that is invisible in normal daylight, but glows when placed under UV lights. They tuned these two light-up mechanisms to different colours, so that the material lights up red when stretched, green when under UV light, and yellow when both happen at once.
Zeng says that the material held up after thousands of cycles of stretching and releasing, so it could be used in bank notes to make them harder to copy.
Advanced Functional Materials
