Researchers at ITMO University in St. Petersburg, Russia, have revealed a new approach for printing luminescent structures based on nanoparticle ink. The optical properties of the ink were achieved through europium-doped zirconia. Particles of this material were proven to be useful for manufacturing glowing holographic coatings with a high degree of protection. The new approach allows for the fabrication of custom holograms by means of a common inkjet printer. Inkjet printing with functional nanoparticles had been gaining a lot of interest in recent years. There are a number of advantages for luminescent nanoparticles, such as a lack of toxicity, high refraction index, and high quantum yield. More applications for luminescent nanoparticles are being found in the fields of photonics, theranostics and bioimaging. They can be used to produce biosensors, visualize cancer cells, and also in security printing technology. To implement lab-made solutions on a larger scale, there are a number of steps that need to be undertaken to ensure proper functionality and stability during long-term storage of holograms. The new ink possesses characteristics that address these issues, said researchers. In a series of experiments, the material was used for printing monolayers of luminescent-protected holograms and anti-counterfeiting objects with high stability and durability.
“Europium-doped zirconium dioxide is a material that’s been studied and used by researchers all over the world for decades,” said Alexandr Vinogradov, co-author of the research and head of ITMO University’s Biochemistry Cluster. “However, our research is novel in that it uses the material to protect the surface of rainbow holograms. To this end, we had to achieve certain features in the material. In particular, the nanoparticles contained in the ink must be close to identical in size. Strict requirements are also imposed by rheological parameters that determine the viscosity of the material – otherwise the ink might not be suitable for inkjet printing. Our goal was to transform a material that was initially synthesized in a test tube, into a stable colloid that could be printed and applied to any surface. Our study describes the exact process of creating such functional ink.”
This is not the first research into inkjet printing of luminescent optical nanostructures that’s been done at ITMO University. The study builds on previous work conducted as part of a larger project funded by the Russian Science Foundation. The same team of scientists developed the world’s first method of printing holographic images using an inkjet printer. Back then, the team used ink based on titanium dioxide. One of the promising applications for the new ink is in the field of security printing, such as the polygraphic manufacture of bills, bonds and documents. Unlike the technologies that currently exist, the new method makes it possible to create varied individual holograms on an industrial scale – such as a specific pattern or number sequence on a document that requires protection. The researchers say that the product is now ready for practical applications. The ink is compatible with currently existing printhead types and can be used with existing manufacturing capabilities.