​Eu was implanted into high quality cubic zincblende GaN ZB−GaN layers grown by molecular beam epitaxy. Detailed structural characterization before and after implantation was performed by x-ray diffraction XRD and Rutherford backscattering/channeling spectrometry. A low concentration (≪10%) of wurtzite phase inclusions was observed by XRD analysis in as-grown samples with their 0001 planes aligned with the {111} planes of the cubic lattice. Implantation of Eu causes an expansion of the lattice parameter in the implanted region similar to that observed for the c-lattice parameter of wurtzite GaN W−GaN. For ZB-GaN:Eu, a large fraction of Eu ions is found on a high symmetry interstitial site aligned with the <110> direction, while a Ga substitutional site is observed for W-GaN:Eu. The implantation damage in ZB-GaN:Eu could partly be removed by thermal annealing, but an increase in the wurtzite phase fraction was observed at the same time. Cathodoluminescence, photoluminescence PL, and PL excitation spectroscopy revealed several emission lines which can be attributed to distinct Eu-related optical centers in ZB-GaN and W-GaN inclusions.