Abstract The luminescence properties of MoO 2− 4 and MoO 6− 6 complexes are reported and discussed, using new data on La 2 MoO 6 and ordered perovskites. In the molybdate complexes the probability of nonradiative return to the ground state decreases if the lowest absorption band is at higher energy and the Stokes shift decreases. In the perovskite Ba 3 Y 2 MoO 9 the Mo 6+ and Y 3+ ions show 1 : 2 ordering. A small amount of disorder is probably due to interchange of some of the Ba 2+ and Y 3+ ions.