Context: The Indian scientists have developed a special safety ink that can help in counterfeiting documents such as passports, packing fake medicines and counterfeiting currency notes. This ink shows two colours when exposed to the light of a certain frequency.

• It has been developed by scientists from the National Physical Laboratory (NPL) of the Council of Scientific and Industrial Research (CSIR), New Delhi and the Academy of Scientific and Innovative Research, Ghaziabad. The study has been published in the Journal of Materials Chemistry-C.

About Bi-luminescent security ink

• This ink reflects two colours when exposed to the light of a certain frequency. This ink appears white in normal light. However, when ultraviolet light is applied at a frequency of 254 nanometers, it emits a red colour. Similarly, when ultraviolet light is switched off, it emits a green colour.
• This newly developed ink emits red color at a frequency of 611 nanometers and green color at a frequency of 532 nanometers due to exposure to ultraviolet light. The red colour emits due to the fluorescence and the emission of green color is due to the phosphorescence effect.

Benefits

• At present, a pack of one kilogram has been delivered to Bank Note Press (BNP), Dewas and Security Printing Meeting Corporation of India Limited (SPMCIL), New Delhi. 
• The ink is found comparable to the standards that are in use. The formulation can be used to check the authenticity of passports, Government documents, tamper evident labels, identity cards, etc.

Production of security ink

• According to the reports, the two colors are mixed in a ratio of 3: 1 to obtain the required properties of the ink. A team of scientists heat treated this mixture for three hours at 400-degree temperature. In this way, fine white powder was developed to produce two-color emitting ink at the frequency of one wavelength.
• Scientists said that chemical elements have been thermally treated to ensure the pigments stick to each other at the production level. The powder is finally mixed with polyvinyl chloride (PVC) to obtain a shiny safety ink.