Researchers from Nottingham Trent University have developed liquids that remain liquid at room temperature and contain chemical elements that produce characteristic glow patterns. According to the authors, such materials could offer a flexible approach to optical tagging and anti-counterfeiting protection, and are also compatible with existing processing and printing technologies.
The work concerns ionic liquids - salts that remain liquid at relatively low temperatures - combined with lanthanides. Lanthanides are a group of 15 metallic elements, some of which have the ability to emit light. Under ultraviolet light, each of them produces its own set of wavelengths, creating a unique optical fingerprint.
The team obtained four different luminescent liquids that are easy to mix with each other; each contains one of the lanthanide elements. Instead of developing and producing a new material for each security code, these liquids can be combined in different proportions.
In a study conducted jointly with the Universities of Liverpool and Manchester, the scientists demonstrated mixtures with two lanthanides, as well as more complex combinations of three and four components. The mixtures produced increasingly complex light signatures while retaining the characteristic glow of the individual components. This means that a much wider range of optical signatures can be obtained from a relatively small number of base materials without additional chemical synthesis.
Many modern security systems rely on elements that are difficult to reproduce - special inks, holograms or other optical effects. The researchers wanted to find out whether materials with complex light signatures could provide an additional level of protection.
A security mark applied with one of these liquids may look ordinary under normal lighting, but under ultraviolet light it reveals a characteristic pattern. The team demonstrated the materials on paper: different liquids and their mixtures produced different optical responses when irradiated with ultraviolet light at different wavelengths.
The initial work showed the potential of the materials, but further research is needed to fully understand how they will behave in real-world conditions.
"This could find application in optical tagging and security identification, including anti-counterfeiting technologies," said senior author Dr Anthony Fitzpatrick, a researcher at the School of Science and Technology at Nottingham Trent University. "The materials could potentially be incorporated into printed security elements or other systems where a distinctive optical response is used to confirm the authenticity of a product."
"Creating a more complex security signature does not require creating more complex materials. Instead, different luminescent liquids can be combined to produce new signatures. This could simplify adapting the approach for different tasks, allowing manufacturers to create custom optical tags or identification systems without the need to synthesize a new material for each application," he added.
Nottingham Trent University postgraduate student Annie Prasad noted: "The key feature is that the new materials remain liquid at room temperature, which makes them more convenient for mixing and preparing formulations than materials that must be processed as solid compounds. In addition, their properties could make them suitable for processing and printing technologies already used to create security marks."
The study was published in the journal RSC Advances.