We extend the use of Raman spectroscopy to investigate the modes of Er-implanted and Er+O co-implanted GaN, and discuss the influence of O ions on Er3+-related infrared photoluminescence (PL). It is found that Er3+ implantation introduces new Raman peaks in Raman spectra at frequencies 300 and 670 cm-1, and one additional new peak at 360cm-1 is introduced after Er+O implantation. It is proposed that the broad structure around 300 cm-1 mode originates from disorder-activated scattering (DARS). The Raman peak at 670 cm-1 is assigned to nitrogen vacancy related defects. The 360 cm-1 peak is attributed to the O implantation induced defect complexes (vacancies, interstitial, or anti-sites in the host). The appearance of the 360 cm-1 mode results in the decrease of the Er3+-related infrared PL of GaN:Er+O.