The mixed phases of the un-doped MgAl2O4/MgO/Sr3Al2O6/SrAl2O4 (MMSS), MgAl2O4/MgO (MM) Sr3Al2O6/SrAl2O4 (SS), and the doped MMSS:x% Er3+ (0 ≤ x ≤ 1.8) nanopowders were synthesized using the citrate sol-gel method. The effect of Er3+ concentration on the structure, morphology and optical properties were investigated. X-ray powder diffraction (XRD) analysis indicated the cubical MgAl2O4, MgO and Sr3Al2O6; and monoclinic SrAl2O4 phases. The scanning electron microscopic images revealed the transformation of irregular particles to rod-like structure with an increase in Er3+ concentration. Transmission electron microscope indicated the nanosized particles depends on Er3+ concentration. Severals distinct absorption bands located at 444, 546, 653 and 704 nm under UV excitation (285 nm) corresponding to the defects states of the MgAl2O4, MgO, SrAl2O4, and Sr3Al2O6 phases were observed. There were traces of emission peaks at 546 and 653 nm attributed to the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ion. An exponential decrease in luminescence was observed with an increase in Er3+ concentration.