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A large number of epitaxial GaN samples as well as AlN ceramics have been studied by photoluminescence (PL) and PL excitation spectroscopy. In addition to the PL of residual iron, two new bands with zero-phonon-lines at 0.931 and 1.193 eV have been observed frequently in GaN. An analysis of the PL bands indicates that they arise from internal transitions within the 3d shell of residual vanadium and chromium impurities. The chromium PL has also been observed in polycrystalline AlN ceramics.
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Baur et al. (1995) studied this question.
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