Density functional studies of defects and defect-related luminescence in Mg3N2

$\mathrm{M}{\mathrm{g}}_{3}{\mathrm{N}}_{2}$ is a promising material for light-emitting-diode applications. However, the microscopic origin of the broad yellow photoluminescence in $\mathrm{M}{\mathrm{g}}_{3}{\mathrm{N}}_{2}$ remains unknown. Here, defect properties and defect-related optical transitions are investigated based on the hybrid functional calculation. Our results show that the nitrogen vacancy introduces multiple localized defect states within the band gap, which play a dominant role in luminescent properties of $\mathrm{M}{\mathrm{g}}_{3}{\mathrm{N}}_{2}$. Common impurities like hydrogen, oxygen, and carbon and their complexes with native defects are also studied. Compared with isolated ${\mathrm{V}}_{\mathrm{Mg}}, {\mathrm{V}}_{\mathrm{Mg}}$-H and ${\mathrm{V}}_{\mathrm{Mg}}\ensuremath{-}{\mathrm{O}}_{\mathrm{N}}$ complexes have shallower transition levels. Our calculated optical excitation and emission peaks associated with isolated ${\mathrm{V}}_{\mathrm{N}}$ are in good agreement with those observed in experiments. In addition, the impurity ${\mathrm{C}}_{\mathrm{N}}$ is also a potential source for the observed yellow emission in $\mathrm{M}{\mathrm{g}}_{3}{\mathrm{N}}_{2}$.