Phosphor performance is often limited by preparation conditions which determine the degree of crystallinity and structural order. The influence of vacancy disorder was investigated using magnesium aluminate and magnesium gallate spinels as test cases. Spinels of composition Mg1-xAl2O4-x:Mn2+ and Mg1-xGa2O4-x:Mn where 0 < x < 0.2 form defect solid solutions in which the loss of the divalent cation is compensated by the formation of both anion and cation vacancies. Defect and normal/inverse disorder was probed by comparing the emission and excitation spectra of Mn2+. MgAl2O4:Mn2+ emits at 650 nm. When x= 0.05, emission bands appear at 517 and 744 nm. These increase intensity and the 650 nm band disappears as x increases. The emission of the magnesium gallate phosphors was a single band at 507 nm for all compositions. Overall, the emission spectra were determined more by the distribution of Mn2+ over the available sites than by either normal/inverse disorder or defect disorder.