Normalised 14 K PL and PLE spectra for the as-grown and Eu-implanted GaN QD/AlN SL structures. Black full lines: PL spectra obtained with excitation with photons of 3.81 eV energy (He-Cd laser line); lines and closed symbols: PL spectra obtained with excitation of 4.7 eV. Dashed lines: PLE spectra monitored at the maxima of the low energy broad emission band. (i) stands for sample 987 which was implanted with 1 × 1015 atoms.cm-2 and annealed at 1000°C (a), 1100°C (b) and 1200°C (c). (ii) stands for sample 989 which was implanted with 1 × 1013 atoms.cm-2 (a) and 1 × 1014 atoms.cm-2 (b) and annealed at 1000°C.