GaN thin films grown on sapphire were implanted by Eu^3+ with three different fluences (5.0×10~14 , 2.5×10~15 and 5.0×10~15cm^-2 ). The photoluminescence (PL) spectra show that, after annealing, the samples exhibit strong emission at around 622.0 nm under 325 nm laser excitation. The intensity of this emission increases by one order of magnitude after annealing at from 600 ℃ to 900 ℃. Moreover, it increases less than 2 times when the fluence increases from 5×10~14 cm^-2 to 5×10~15 cm^-2 for the sample annealing at 900 ℃. The PL emission peaks around 622 nm of samples annealing at 900 ℃ can be well clarified by Gaussian fitting into 620.2, 622.0 and 625.0 nm, which are due to the Eu^3+ related with defects, Eu^3+ occupied at substitutional positions of Ga, and that located at interstitial sites, respectively. It shows that the different microenvironments and positions of Eu^3+ are responsible for these peaks, and especially the defects introduced by implantation play an important role in the behavior of the PL because they set up an energy transmission bridge from exotic photons to Eu^3+ .
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