The defective fluorite-related Y3NbO7 host lattice was doped with Eu3+ ions to understand the influence of spark plasma sintering (SPS) process on this host lattice. The intrinsic disorder due to the occurrence of oxygen vacancies results in amorphous-type responses of the luminescent cations, and the spectral distribution varies as a function of the niobium content. Two spectral fingerprints of europium emissions were clearly enhanced. The correlation between luminescence, X-ray diffraction, and electron diffraction characterizations shows the existence of local inhomogeneity. Indeed, the particular nonequilibrium sintering conditions allowed pointing out a lack of miscibility within the Y3NbO7 solid solution domain. Thus, the SPS pellet is a composite of two extreme compositions. This phase demixing is mainly induced by the pressure coupled with a current effect that makes possible ionic migration in this Y3NbO7 ionic conductive matrix.