Indian team doubles ink security to prevent counterfeiting

• Indian scientists have developed a new ink that can make counterfeiting of documents harder.
• Security printing is a method of creating items with safeguards against counterfeiting, incorporating features that humans can detect.
• Examples include optically variable ink, watermarks, holograms, and security threads.
• Other security-printed features include raised shapes and shifting textures, invisible barcodes, digital watermarks, and holograms.
• The nanoparticle solution is a new ink made using nanoparticles, which are objects less than 100 nm wide.
• The nanoparticles were made of Sr2BiF7 (strontium bismuth fluoride) doped with lanthanide ions, and then doped with ions of erbium and ytterbium, both lanthanide elements.
• The nanoparticles were blended with polyvinyl chloride (PVC) ink and then printed using a screen printing technique.
• The ink emits a cool blue glow under 365-nm wavelength ultraviolet light, making it more secure.
• The low-cost ink remains effective under varied brightness, temperature, and humidity conditions.
• The study was published in ACS Applied Materials and Interfaces in September 2024.
• The ink’s quantum yield is not reported, but it shows good brightness under different excitation wavelengths, sufficient for practical applications.
• The ink is composed of gadolinium vanadate (GdVO4) doped with europium and emits red and green light under ultraviolet light of two wavelengths.