In the paper the effect of light output increase with maximum at x = 0.5 observed previously for the mixed ZnxMg₁₋ₓWO₄ crystals is demonstrated for nanocrystals with the same composition. The enhancement of light output up to 3 times at the transition from bulk to nanosize was shown. This effect is determined by nonlinear dependence of concentration of oxygen vacancies with minimum at x = 0.5 for ZnxMg₁₋ₓWO₄ nanocrystals."