X-ray Induced Hydroxyl Radical Generation by GdYVO₄:Eu³⁺ Nanoparticles in Aqueous Solution: Main Mechanisms

We report on strong X-ray-induced hydroxyl radical (. O H ) generation in an aqueous solution containing UV light pre-treated GdYVO4:Eu3+ nanoparticles (L-GdYVO). The methods of optical spectroscopy were used to detect . O H in the solutions. The complex nature of the mechanism of . O H generation has been revealed and discussed. The experimental data obtained indicate that the mechanism of . O H generation is associated with two main processes: (i) direct . O H generation with the participation of thermalized h+ formed at X-ray irradiation, and (ii) X-ray-facilitated jumps of h+ formed in the nanoparticles’ (NPs’) valence band at UV light pre-treatment and trapped in local levels formed by random scattering potential. At the same time, for GdYVO4:Eu3+ nanoparticles, which were not exposed to UV light before the X-ray irradiation (D-GdYVO), a strong radioprotective effect ascribed to the electron-donation properties of V4+ ions was observed. Thus, depending on the pre-treatment condition, we can change the redox properties of GdYVO4:Eu3+ NPs in an opposite direction, which makes this nanomaterial a unique theranostic agent for radiation therapy (RT) enhancement, allowing the problem of radiation therapy (RT)-resistant hypoxic tumours to be overcome.