The effect of vacancy disorder was investigated in aluminate and gallate spinels. Samples of the form, Al2Mg1-xO4-x:Mn2+ and Ga2Mg1-xO4-x:Mn2+, where x was between 0 and 0.2, formed defect solid solutions in which the loss of the divalent cation was compensated by the formation of both anion and cation vacancies. The defects and disorder were probed by comparing the emission and excitation spectra of Mn2+. The Al2MgO4:Mn2+ emitted at 650nm. When x was equal to 0.05, emission bands appeared at 517 and 744nm. These increased in intensity and the 650nm band disappeared as x increased. The emission of the gallates consisted of a single band at 507nm for all compositions. It was concluded that the emission spectra were determined by the distribution of Mn2+ over the available sites, rather than by normal/inverse disorder or defect disorder.

R.L.Mohler, W.B.White: Materials Research Bulletin, 1994, 29[10], 1109-16