We present a photoluminescence study of residual transition metal contaminants in hexagonal GaN layers. We observe three no-phonon lines peaking at 1.3 eV, 1.19 eV and 1.047 eV. The no-phonon line at 1.3 eV is caused by the internal electronic transition 4T 1→ 6A1 of Fe3+. The 1.19 eV emission, which was first attributed to Cr4+, is caused by Ti2+. GaN layers intentionally doped with Cr, V, or Ti during growth have been investigated. Only the Ti doped samples snow an intense sienal of the 1.19 eV emission. The experimental data of the luminescence center at 1.047 ev, which appears as natural contaminant only in GaN layers grown by the sandwich technique, fit best to the 4T2(F) → 4A2(F) transition of Co2+. The three no-phonon lines show characteristic phonon sidebands. Most of them correspond to phonon modes observed in Raman spectroscopy.