Optical detection of electron paramagnetic resonance in electron-irradiated GaN

2.5 MeV electron irradiation of wurtzite GaN epitaxially grown on sapphire substrates greatly reduces its near-UV and visible luminescence, producing two bands in the near infrared. In one of these, a broad structureless band centered at ∼0.95 eV, three optically detected $S=1/2\mathrm{}$ electron paramagnetic resonances (ODEPR) are observed. Two of these display well-resolved hyperfine interaction with a single Ga nucleus, suggesting that they are interstitial-Ga related. The second band has a sharp zero-phonon line at 0.88 eV and accompanying phonon-assisted structure and reveals an $S=1\mathrm{}$ ODEPR signal, as yet not identified.