Indigenous anti-counterfeit ink developed by CSIR-NPL

The CSIR-National Physical Laboratory (CSIR-NPL), New Delhi – the laboratory that gave us the indelible ink – is all set to launch a high security ink that makes counterfeiting difficult.

Dr. Bipin Gupta and his team have described a novel process of manufacturing that makes an all-purpose security ink a reality. The process is reported in Chemistry: A European Journal (DOI: 10.1002/chem.201704076).

Security inks are essential and crucial for printing of currency. They help prevent counterfeiting, and in such an event make their detection easy. The first step that we all follow in detection of a counterfeit is to scan it under UV light. One could then clearly see features that are normally not visible, since those features are printed with a special ink that glows – or fluoresces – only when exposed to UV radiations. However, many such inks in use need a special surface that is “UV bland” to be effective. In other words, they need a special paper that itself does not glow under UV light.

Works with all papers and surfaces

The ink developed by Dr. Gupta’s team however does not need such special surfaces. “It is printable on all papers and surfaces,” exudes Dr. Gupta. Not only that, the ink can be tested both under UV and infrared (IR) lights. This dual-mode glowing by the ink adds to its secure nature, making it doubly counterfeit-proof. “The ink is formulated from a cost-effective dual-mode luminescent composite Pigment,” says Dr. Gupta. This is a combination of rare earth elements like gadolinium, Ytterbium and erbium oxides with phosphors such as ZINC and manganese sulphide.

Dr. Gupta’s team has judiciously mixed these two complex chemicals to get a pigment that can be used in the manufacture of ordinary inks. The rare earth metals are in the form of nanorods and respond to near-IR laser while the phosphors respond to UV light. The composite pigment can be excited with two wavelengths – in UV light (365 nm, UV lamp) and 980 nm with near-IR (NIR) laser. The nanorods emit red light upon excitation with 980 nm laser and phosphors emit yellow light upon exposure to 365 nm UV lamp. The ink designed by Dr. Gupta’s team shines bright yellow under UV and intense red when under IR.

“We have plans to replace NIR laser with NIR LEDs in future to make a cost-effective excitation source,” says Dr. Gupta. That would make the lamps cheaper and easy for manufacturing.

More secure

The composite pigments in the ink, Gupta says, are “tunable and thus more secure” – meaning that pigments responding to specific excitation wavelengths and emit specific wavelengths of light are possible. “This makes it extremely difficult to counterfeit,” explains Gupta. In other words, patterns that appear identical on paper or on different currencies may glow differently when exposed to a selected and specific frequency of light. Besides making currency secure, these novel inks can also be used in “printing labels of pharmaceuticals or in printing important documents” says Dr. Gupta.