In this work results of extensive characterization of homoepitaxial layers grown on truly bulk ammonothermal gallium nitride (GaN) substrates are presented. The 2-mu m-thick layers were deposited using metalorganic chemical vapor deposition. The photoluminescence (PL) and reflectance results show very intensive, perfectly resolved excitonic structure in range of band-edge emission of gallium nitride. This structure consists of both lines related to free excitons emission and very narrow lines (full-width at half-maximum (FWHM) value of the order of 0.3 meV) related with excitons bound to neutral acceptor and different neutral donors. In high excitation condition the biexciton emission was observed. The luminescence is uniform in the whole sample surface range. High PL homogeneity corresponds with structural and microscopic measurements performed on these layers. It proves that ammonothermal GaN substrates with perfect crystalline properties enable to grow excellent quality, strain-free hornoepitaxial layers. (C) 2009 Elsevier B.V. All rights reserved.