AlN epilayers with high optical qualities have been grown on sapphire substrates by metalorganic chemical vapor deposition. Deep ultraviolet photoluminescence (PL) spectroscopy has been employed to probe the optical quality as well as optical transitions in the grown epilayers. Band-edge emission lines have been observed both at low and room temperatures and are 6.017 and 6.033 eV at 10 K. It was found that the peak (integrated) emission intensity of the deep impurity related transition is only about 1% (3%) of that of the band-edge transition at room temperature. The PL emission properties of AlN have been compared with those of GaN. It was shown that the optical quality as well as quantum efficiency of AlN epilayers is as good as that of GaN.