Nano-material based security ink developed indigenously to help combat counterfeiting of currency and documents

Vijay Mohan

Tribune News Service

Chandigarh, October 26

A highly stable and non-toxic luminescent security ink has been developed indigenously from nano-materials that will help combat counterfeiting of currency-notes, medicine, certificates, documents and branded goods.

Counterfeiting is very common all over the world and it has become a serious issue. Luminescent ink is generally used as covert tags to combat the counterfeiting. Most security inks available today are based on luminescent materials that absorb a high energy photon and emit low energy photon.

This is technically called ‘downshifting’ where the covert tag remains invisible under daylight but becomes visible under ultra-violet light. However, these single emission-based tags are prone to replication.

To overcome this drawback, luminescent ink with excitation-dependent luminescent properties, that is both downshifting and upconversion are advised. This is because increasing the number of parameters required to decode the tag decreases the possibility of decoding and replication. Most materials being used for this purpose are based on fluorides which are less stable and highly toxic.

A team from the Institute of Nano Science and Technology, Mohali, led by Dr Sanyasinaidu Boddu, has developed non-toxic metal phosphate-based ink with excitation dependant luminescent properties which are highly stable under practical conditions such as temperature, humidity and light.

The luminescent security ink developed by the researcher showed very strong downshifting as well as upconversion properties. Also, the downshifting luminescence colour of the ink is highly dependent on the excitation wavelength, making it difficult to decode the covert tag.

These luminescent nano materials were synthesised via a simple co-precipitation method. A composite was made with these nano particles and commercially available PVC gold medium ink. The composite ink was used to print patterns and letters on black paper. The patterns of this ink under different excitation wavelengths were found to be stable against various conditions which may occur during practical applications.

“The trivalent lanthanide ions that have been used have very rich energy levels which help to absorb a high energy photon and emit low energy photon, as well as absorb low energy photon and emit a high energy photon,” Dr Boddu said.

“The nano-particle lanthanide ions are known for their excellent downshifting and upconversion luminescent properties. We thought that if these materials are applied for anti-counterfeiting, it will give better encoding, decoding capacity and thereby improve security features,” he added.

The developed ink has huge potential to combat counterfeiting and the common man can find out easily whether the document or product is original or fake, according to a statement issued by the Ministry of Science and Technology today. The research has been published in the journals, Crystal Growth and Design and Materials Today Communications.