We report the morphological and compositional characteristics and their effect on optical properties of Er-doped GaN grown by solid source molecular beam epitaxy on sapphire and hydride vapor phase epitaxy GaN substrates. The GaN was grown by molecular beam epitaxy on sapphire substrates using solid sources (for Ga, Al, and Er) and a plasma gas source for N-2 The emission spectrum of the GaN:Er films consists of two unique narrow green lines at 537 and 558 nm along with typical Er3+ emission in the infrared at 1.5 mu m. The narrow lines have been identified as Er3+ transitions from the H-2(11/2) and S-4(3/2) levels to the I-4(15/2) ground state. The morphology of the GaN:Er films showed that the growth resulted in either a columnar or more compact structure with no effect on green light emission intensity.