Abstract The luminescence and energy migration characteristics of the isostructural systems LiGd1−xEuxF4 and Gd1−xEux NbO4 are reported and compared. In both lattices vibronic coupling is observed in the optical transitions of the Eu3+ ions. The energy migration process in LiEuF4 and EuNbO4 is diffusion limited and takes place via exchange interactions between the Eu3+ ions. In EuNbO4 superexchange via niobate groups plays also a role. The Eu3+ -Eu3+ transfer process at low temperatures is two-phonon assisted according to the two-site non-resonant mechanism. For both concentrated compounds the Eu3+ -Eu3+ transfer probability at room temperature is about 107 s-1. The different ligands of Eu3+ in the fluoride and niobate lattice cause striking differences in the radiative decay time т0, the intensity of the vibronic lines, and the number of neighbours N to which an excited Eu3+ can transfer its energy; Li(Gd, Eu)F4: т0 = 7.3 ms, N = 4; (Gd, Eu)NbO4: т0 = 640 μs, N = 8.