Abstract <p>Visible-light photocatalysts based on nitrogen- and carbon-doped nanocrystalline titanium dioxide microspheres have been synthesized. Their structural, optoelectronic, and photocatalytic properties have been studied. Electron paramagnetic resonance was used to identify spin centers (defects) and determine their concentration in all samples under study. In nitrogen-doped microspheres, nitrogen atoms with an unpaired electron and Ti³⁺/oxygen vacancy centers were found. In carbon-doped microspheres, dangling carbon bonds were detected. Photocatalysts doped simultaneously with nitrogen and carbon contain both nitrogen and carbon spin centers. It has been found that the concentration of defects increases during illumination, which is explained by their recharging. A correlation has been established between the concentration of spin centers and the rate of photocatalysis in the obtained structures. It has been demonstrated that samples doped with two impurities are characterized by a high rate of photocatalysis and prolonged catalysis for 30 min after switching off the light, as well as stable photocatalytic properties for several years, which determines the novelty of the studies performed and high potential for use in ecology and biomedicine.</p>