Governments and monetary establishments take painstaking efforts to consolidate banknotes, cheques, and passports with quite a lot of security measures to defend them from counterfeiting. Yet every now and then a counterfeiter emerges who can recreate these options and cross off pretend paperwork as actual ones. In response, establishments always develop newer and higher parts which are even more durable to falsify.
Now, scientists from India have provide you with an ink they are saying could make counterfeiters’ jobs more durable.
Security printing
Counterfeiting is a severe menace to a variety of enterprises. Spurious medicines packaged to appear like the true factor can delay correct therapy and even kill. Branded shopper items nowadays have tamper-resistant packaging to stop cheats from promoting low-quality replicas.
The printing of things with safeguards towards counterfeiting is named safety printing. It implements options that people can detect by themselves or utilizing easy instruments. Examples embody optically variable ink (whose color seems to change when considered from totally different angles), watermarks, holograms, and safety threads. Features like raised shapes and shifting textures are security-printed options an individual can verify utilizing the sense of contact.
Security printing can even incorporate extra advanced options that solely machines can detect. Some fashionable passports embody a small radio-frequency identification chip that solely a scanner can learn. Other examples embody invisible barcodes, digital watermarks, and holograms.
A nanoparticle answer
An essential security-printed characteristic on Indian banknotes is a quantity panel in fluorescent ink situated on the decrease left nook. The numbers listed here are seen solely in ultraviolet gentle.
Scientists from the Institute of Nano Science and Technology (INST), Mohali, and the Bhabha Atomic Research Centre (BARC), Mumbai, have now reported a brand new ink they’ve made utilizing nanoparticles. Nanoparticles are objects lower than 100 nanometres (nm) extensive. Because of their small dimension, they’ve properties that don’t seem in bigger objects: they work together in a different way with gentle, reply in a different way to magnetic fields, and are chemically extra reactive.
That the invention of the way to manufacture semiconductor nanoparticles with uncommon properties gained three scientists the 2023 Nobel Prize for chemistry speaks to nanoparticles’ transformative impact on the world.
A easy recipe
In the brand new research, the nanoparticles have been fabricated from Sr2BiF7 (strontium bismuth fluoride) doped with lanthanide ions. Doping is the method of intentionally including impurities to an present crystal to give it properties it beforehand didn’t have.
Scientists used the coprecipitation method to make the particles. “To do this, all the metal salts in the required quantity are dissolved in a suitable solvent. Once you get a clear solution, the required amount of precipitation agent is added while stirring,” INST scientist and research coauthor Sanyasinaidu Boddu mentioned. Then they used a centrifuge to separate the deposited materials out.
“The proposed compound is a new composition and is the first time we have synthesised it by a simple coprecipitation method at just above room temperature, which is very easy to scale up,” Boddu added.
The team then doped the Sr2BiF7 nanocrystals with ions of erbium and ytterbium, each lanthanide components, and blended them with simply out there polyvinyl chloride (PVC) ink. Finally, they used the display screen printing method to print some letters and numbers. Screen printing makes use of a stencil and a squeegee to switch a picture onto paper.
Two-light trick
When the researchers shone 365-nm wavelength ultraviolet gentle on these symbols, they emitted a cool blue glow. This course of is named fluorescence: when an object absorbs gentle of 1 wavelength and emits gentle of an extended wavelength. Under 395-nm gentle, the letters glowed magenta. And when the researchers directed close to infrared gentle of 980 nm on the letters, they fluoresced with an orange-red color.
According to the team, at present out there fluorescent inks are seen solely underneath both ultraviolet gentle or infrared gentle however not each, including that their ink stands out as a result of it fluoresces in each the ultraviolet and the near-infrared components of the spectrum. This, they contended of their paper, makes their ink extra secure.
This low-cost ink additionally stays efficient underneath assorted brightness, temperature, and humidity situations.
The research was printed in ACS Applied Materials and Interfaces in September 2024.
Towards sensible use
Bipin Kumar Gupta, senior principal scientist and professor on the CSIR National Physical Laboratory in New Delhi, who wasn’t concerned within the research, mentioned the paper didn’t report the quantum yield of the system. Quantum yield specifies how properly the system converts incident gentle into fluorescence.
“Quantum yield is crucial for applications such as light emitting diodes and display devices. However, a very high quantum yield is not necessary for security applications. … From our report, it is very clear that the material is showing very good brightness under different excitation wavelengths, and that is sufficient for practical applications,” Boddu mentioned.
Gupta obtained an Indian patent for a bi-luminescent safety ink on January 30, 2025, after a US patent for a similar object in February 2022. This ink consists of gadolinium vanadate (GdVO4) doped with europium and emits pink and inexperienced gentle underneath ultraviolet gentle of two wavelengths.
“To print security features on, say, currency notes, generally offset printing and not screen printing is used,” Gupta mentioned when requested concerning the applicability of the ink developed at INST.
Offset printing makes use of a system of three rollers. One cylinder ‘offsets’ the picture from a metallic plate to a rubber blanket. The picture is then transferred to the printing floor. Offset-printed photos are sharper and able to printing smaller letters.
“I agree that screen printing is not used for currency notes. However, there are many other places where you can use screen printing … We are [also] working towards offset printing.” Boddu mentioned. “There are a few more steps to take this material to direct practical applications, and we are working on these steps.”
Unnati Ashar is a contract science journalist.
Published – March 10, 2025 05:30 am IST
