Researchers develop invisible colour-changing material for anti-counterfeit tags

Scientists at the University of Turku have created davyne, a material that shifts colour in the near-infrared range and can only be detected with special cameras or spectrometers. The finding could lead to new security markings for banknotes, passports and other documents.

Why it matters: - Davyne could add a new layer of protection against counterfeiting on banknotes, passports and other official documents. - The material’s colour change is invisible to the human eye, which makes it harder to copy or spot without the right equipment. - The colour change can be switched on and off, giving inspectors a way to reveal and then hide the marking.

What happened: - Researchers at the University of Turku developed a new material called davyne while studying the properties of hackmanite. - The material changes colour in the near-infrared region, not in visible light. - The study was published in Angewandte Chemie. - The work involved the Intelligent Materials Chemistry Group, the Department of Materials Engineering and the Department of Physics and Astronomy at the University of Turku. - Research partners included Aalto University, the National Institute of Chemical Physics and Biophysics in Tallinn, and the University of Lyon.

The details: - Hackmanite is a natural mineral that can also be made synthetically. - Hackmanite turns from white to pink or violet under UV exposure, then returns to its original colour under white light or when heated to 100°C. - The new material emerged when calcium was introduced into hackmanite instead of sodium. - That change produced calcium hackmanite, which turned yellow. - Some samples showed no visible colour change, but did show changes in the near-infrared range. - Davyne was produced as a by-product of calcium hackmanite synthesis. - Calcium hackmanite and davyne share the same chemical formula, but their atomic structures differ. - Davyne belongs to the cancrinite mineral family. - The team had difficulty producing pure davyne at first because the chemistry tended to shift toward calcium hackmanite. - The researchers optimized the process with help from materials engineering researchers and machine learning methods. - The team eventually produced the purest possible form of davyne. - The researchers showed that davyne’s colour-changing mechanism is similar to hackmanite’s. - The mechanism involves electron transfer to a chlorine vacancy in the structure. - Davyne has long, empty tunnels rather than the cavities typical of hackmanite. - The researchers say davyne is the only known material whose colour change cannot be detected with the human eye. - The team tested the material’s use in security markings with an inexpensive camera after removing its colour detection filters. - The camera’s remaining silicon chip detected a wavelength range suited to davyne. - The tests showed that davyne’s colour change is clearly detectable under infrared light when camera sensitivity is adjusted to the material.

Between the lines: - The study points to a practical route for invisible authentication marks that can be revealed during inspection and then hidden again. - The use of a low-cost camera suggests the detection system may be simpler than some specialty security tools. - The work also shows how small changes in composition can produce a different structure and a different optical response.

What's next: - The researchers say davyne could be adapted for authenticity and security markings in official documents and consumer products. - Further development would likely focus on turning the lab result into a durable marking system that can be manufactured at scale. - The strongest near-term use case is anti-counterfeit labeling where hidden verification matters more than visible branding.

The bottom line: - Davyne gives researchers a rare invisible colour-changing material with a clear anti-counterfeit use case, and the University of Turku team has already shown it can be detected with simple infrared equipment.