Abstract The excitation and emission transitions involved in the green luminescence of the octahedral UO 6- 6 group in oxides with perovskite structure are reported and discussed. The excitation bands are assigned to charge transfer transitions involving the 5f state of the uranium ion. The emission is a parity-forbidden charge transfer transition 5f → t 1u vibronically allowed by coupling with the ungerade vibrational modes of the UO 6- 6 octahedron. The vibrational pattern in the emission of the UO 6- 6 group is different from that of the uranyl ion. From measurements as a function of the uranium concentration it is deduced that energy transfer between uranate groups mutually proceeds over some 25 A.