Optical absorption of lithium nitride

The optical absorption of Li3N single crystals has been measured in the energy range 1–7 eV at various temperatures between 4.2 and 300 K in the two polarizations E∥c and E⊥c for the two crystal orientations k∥c and k⊥c. Strongly anisotropic behavior of the optical absorption edge is reported. The energy gap in the E∥c polarization is indirect with EG=2.15 eV at 4.2 K and EG=2.00 eV at 300 K. Two peaks in the absorption edge E⊥c are ascribed to the creation of excitons, which are bound to directionally arranged defect complexes.