Sol-gel synthesis of the (GdxY1–x)2O3: Eu3+ solid solutions (3.5 mol %) allows for the increase in the energy efficiency of emission of the red luminophor. The study of distribution of the luminescence activator Eu3+ has revealed that these ions substitute the Gd3+ ones in the cationic sublattice of ternary solid solution. The Eu3+ ions are predominantly localized in the noncentrosymmetrical position C2 at x < 0.50 and in centrosymmetrical position C3i at x > 0.50. The increase in the Eu3+ ions concentration in the C3i position stabilizes the cubic high-temperature structure of the solid solution in comparison with the monoclinic phase. The solid solution with x = 0.75 has been found to be the most efficient luminophor.