The possibility of using alloys based on magnesium modified by plasma-electrolyte treatment for photocatalysis purposes is considered. A brief description of the nature of the occurrence of photoactivatable centers in oxides is given; examples of similar studies in the field are provided. Under the assumption of photogeneration of plasmon and exciton quasiparticles, a conceptual model of photosensitization of dielectric oxides has been proposed. Using simulation software COMSOL Multiphysics, numerical calculations were performed to determine the conditions for the occurrence of resonant phenomena in nanoscale MgO. The results of experiments to evaluation of the photocatalytic ability of the Mg–8Li–1Al-0.6Ce-0.3Y ultralight alloy after plasma-electrolyte treatment are presented.