Dawn of Europium: new materials from rare earths will help create sensors of the future

Scientists have found a way to create materials with specified properties based on europium, a rare—earth metal that emits a red glow under ultraviolet light, using various alcohols in production. The proposed method made it possible to regulate the structure of substances, their stability and luminescence efficiency. At the same time, unstable compounds eventually rebuilt themselves into durable polymers that glowed brighter than their counterparts and could withstand heating up to 300 °C. The data obtained will make it possible to synthesize new compounds with controlled optical properties for biomedicine, the creation of smart sensors and sensors, as well as to protect money and documents from counterfeiting.

Rare earth metal europium

Researchers from the Lebedev Physical Institute of the Russian Academy of Sciences, the National Research University Higher School of Economics and Lomonosov Moscow State University have proposed a method for the production of europium compounds. They make materials that can be given a specific structure and properties.

New materials can be given a specific structure and properties by dissolving europium chloride with an "antenna" ligand in different alcohols. The scientists synthesized experimental samples using seven different alcohols. In all cases, the complexes formed as crystals of various shapes and sizes. The resulting compounds were initially unstable, however, when the alcohol evaporated in air or when heated, the substances acquired the same structure in the form of a polymer, a strong molecular chain.

The authors examined the structure of eight samples (seven molecular complexes and one polymer formed on their basis) using X-rays. An additional bond of europium was formed in the polymer with the "antenna" ligand of a neighboring molecule, which gave the material strength.

The chemists also studied the physico-chemical properties of all the obtained materials and tested their ability to luminesce — to emit light under the influence of ultraviolet radiation. The luminescence of the polymer turned out to be 1.5–3 times more intense than that of unstable samples.

The polymer also had a unique luminescent "fingerprint": it emitted bright light in those ranges where the glow of other samples faded.

— No more than ten similar polymer complexes without an additional neutral ligand are known in the world. At the same time, ours turned out to be the most stable and most effective in luminescence. The study helped to understand how to form such structures. At the next stage, we plan to apply this knowledge to the synthesis of rare earth compounds with other antenna ligands with similar chemical structures, as well as to study their properties," Victoria Goncharenko, a junior researcher at the Laboratory of Molecular Spectroscopy of Luminescent Materials at the Lebedev Physical Institute of the Russian Academy of Sciences, told Izvestia.

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The resulting substance can be used to mark banknotes and valuable documents to protect them from counterfeiting, the scientists said. In addition, the results of the study open the way to the creation of new synthetic medical materials for the diagnosis of pathological changes in tissues. The compounds synthesized by the new method will also be useful in the production of sensors for industrial monitoring, such as detecting leaks of harmful compounds.

New europium-based materials open up broad prospects in biomedicine, security, sensors and optoelectronics. Their high—tech properties are significantly superior to existing analogues, Ilya Arkhipov, an expert at Boiling Points Krasnoyarsk, associate professor at Siberian Federal University, told Izvestia.

— Europium materials will find application in biomedicine due to their luminescent properties. They can improve the properties of medical implants. They can also stimulate vascular growth and accelerate tissue healing. The new materials are thermally stable up to 300 °C. This makes them reliable for protection in industry. In sensors and optoelectronics, Europium materials are also in demand due to their high sensitivity, heat resistance and efficiency," the specialist noted.

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This research is important for two reasons, said Anton Muravyov, Candidate of Chemical Sciences, Associate Professor at the ITMO Scientific and Educational Center for Infochemistry. Firstly, for the first time, it was possible to find out how solvent alcohol molecules affect crystal engineering and the photophysical properties of europium complexes. This discovery is of great importance for supramolecular chemistry and the creation of new materials.

— Secondly, scientists have shown how it is possible to control the formation of molecular complexes and polymer structures by changing the external conditions. This can help in the development of materials with specified properties. Further study of these compounds will allow not only to better understand the effect of the solvent on the photophysical properties of europium, but also to explore their application in biomedical imaging. In addition, these materials may become promising for nanoelectronics due to their nanoscale architecture and controlled luminescence," the scientist said.

The results of the study, supported by a grant from the Russian Science Foundation (RSF), are published in the journal Organic Chemistry Communications.