The current work is devoted to a photoluminescence study of high-pressure high-temperature diamonds synthesized in the Mg-Ge-C system. The diamond crystals were shown to contain optically active nitrogen-vacancy, silicon-vacancy and germanium-vacancy centers. Lifetime measurements were carried out for the promising negatively charged germanium-vacancy center (GeV−). The delay between the excitation laser pulse (λex = 375 nm) and the fluorescence of the GeV− center was observed. The excitation transfer was considered as a possible explanation of this phenomenon.