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The optical properties of molecular-beam-epitaxy-grown GaN with different Mn-doping levels (5–23×1019 cm-3) were studied by cathodoluminescence (CL) and optical transmission spectroscopy. Transmission measurements at 2 K revealed an absorption peak at 1.414±0.002 eV, which was attributed to an internal 5T2→5E transition of the neutral Mn3+ state. The intensity of this Mn-related transmission peak was found to scale with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm-3 reduced the near band edge emission intensity by around one order of magnitude. A complete quenching of the donor–acceptor-pair band at 3.27 eV and strong decrease of the yellow luminescence centered at 2.2 eV were attributed to a reduced concentration of VGa. In the infrared spectral range of 0.8–1.4 eV three broad, Mn-doping related CL emission bands centered at 1.01±0.02, 1.09±0.02, and 1.25±0.03 eV were observed. Their origin is attributed to deep donor complexes, which are generated as a result of the heavy Mn-doping. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]