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To better understand the scintillation properties of gallium nitride, a detailed characterization of Metal Organic Vapour Phase Epitaxy (MOVPE) grown GaN layers doped with Ge is conducted. This study includes the measurements of radioluminescence and photoluminescence spectra, thermally stimulated luminescence as well as scintillation decay kinetics. The representative radio- and photoluminescence spectra are composed of two bands. The narrow and fast band peaking at about 3.4 eV is ascribed to excitons and the broad and slow defect-related band with the maximum at about 2.2 eV is produced by carbon occupying nitrogen site. It has been found that the decay kinetics and amplitude of the exciton and defect emission are sensitive to the Ge doping level. In particular, the exciton- and the defect-related luminescence become faster with increasing Ge content. Charge trapping processes were also affected by the Ge doping.