A comprehensive study of the yellow photoluminescence (YL) in GaN epitaxial films grown by hydrid vapor phase epitaxy and by metal organic vapor phase epitaxy is presented including time-integrated and time-resolved photoluminescence (PL), PL excitation (PLE) and optically detected magnetic resonance (ODMR) experiments. ODMR reveals the participation of shallow and deep double donors based on the analysis of the g-values. This recombination model is supported by time-resolved investigations. PLE spectra show a close connection between the excitation processes of the YL band and of the inner transition of Fe3+ at 1.293 eV. Two-color stimulation experiments prove energy transfer between YL and the Fe3+ center by hole transfer, strongly confirming the YL recombination model involving a deep level 1.2 eV above the valence band.