GaN(0001) epilayers grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD) have been irradiated with 75 MeV Sn5+ ions at the fluences of 10(11), 10(12), and 10(13) ions/cm(2). Structural and optical studies reveal that GaN epilayer withstands 75 MeV Sn5+ ion irradiations up to 10(11) ions/cm(2) ion fluences. High resolution X-ray diffraction results showed that the FWHM corresponding to (0002) plane increased from 227 to 279 arc-seconds after Sn-ions irradiation. Red shift was observed in the yellow luminescence (YL) emission by photoluminescence (PL), corresponds to the concentration of ion fluences. Donor-bound exciton (DBE) and free exciton (FEA, FEB and FEC) emissions were observed for as-grown and irradiated GaN samples up to 10(12) ions/cm(2) at 2K PL measurements. Free excitons are dominated by low-temperature PL measurements for as-grown and irradiated GaN samples at 10(11) and 10(12) ion fluences. Atomic force microscopy images show the RMS roughness increases with increasing Sn-ion fluences by removing as-grown GaN surface defects.