Photodynamic therapy (PDT) is already used in medicine today, a method in which a special substance (photosensitizer) is used under the influence of light, it produces reactive oxygen species that destroy mutated cells, including cancer cells. Photosensitizers are actively used to treat skin diseases such as psoriasis, various bacterial infections, or even skin cancer. But this approach has a serious limitation: ordinary light cannot penetrate deep into the tissues, so PDT is used only for the upper layers of the skin. X-ray phosphors solve this problem by allowing this type of exposure to be carried out deeper than in the standard method. Calcium fluoride nanoparticles with europium (Caf₂:Eu) solve this problem by converting X—rays, which easily pass through tissues, into visible light directly inside the body. This opens the way to the treatment of deep-seated tumors without severe side effects.

"The peculiarity of these nanoparticles is that they can emit light of different wavelengths depending on the degree of oxidation of europium. If the material is dominated by Eu2⁺, the glow will be blue, and if Eu3⁺ — orange. This is important because different photosensitizers react to light of different wavelengths. By changing the reaction conditions, it is possible to influence the conditions of defect formation, which, in turn, affects the Eu2⁺ : Eu3⁺ ratio in the material, allowing the creation of particles suitable for specific medical tasks. For example, during ultrasonic synthesis, interstitial fluorine ions are formed in the structure of nanoparticles, which affect their glow and make the material more efficient," says Elizaveta Mukhanova, head of the international research Laboratory of functional Materials.

When such nanoparticles enter a tumor and are X-rayed, they begin to glow, activating a photosensitizer. That, in turn, triggers a chemical reaction to form reactive oxygen species, which kills cancer cells. The advantage of the service: The advantage of europium with different oxidation states over other materials lies in its versatility: due to its wide range of radiation, it can be combined with different photosensitizers, which makes treatment more flexible and personalized.

"Different photosensitizers are activated by different light, which reveals a significant disadvantage of this method – difficulties in selecting a suitable X-ray phosphor. In this case, the material we are studying has additional radiation of a different wavelength, which significantly increases its operating range. We can say that this is a combined approach and the ability, depending on the synthesis conditions, to adjust the phosphor to a wide range of photosensitizers that are available for use or purchase at the moment," notes Kirill Volik, laboratory assistant at the International Research Laboratory of Functional Materials at the SFedU International Research Institute for Intelligent Materials.

Although it is still a long way from being used in the clinic — years of preclinical and clinical research and patenting are ahead — the potential of this technology is obvious. According to the researchers, the next step of this project is to patent a technique for synthesizing phosphors with "personalized" radiation for a wide range of photosensitizers. The use of this material in X-ray imaging is also being considered.

The results of the research, implemented as part of the strategic project of the SFedU "Full-cycle technologies for rapid development of functional materials under the control of artificial intelligence" of the federal program "Priority 2030" (national project "Youth and Children"), are presented in the scientific journal "Journal of Luminescence".