Magnesium Double Nitride Mg₃GaN₃ as New Host Lattice for Eu²⁺ Doping: Synthesis, Structural Studies, Luminescence, and Band-Gap Determination

The double nitride Mg 3 GaN 3 and binary nitride Mg 3 N 2 were synthesized from the elements by reaction with NaN 3 in a sodium flux. Reactions were carried out at 760 °C in welded shut tantalum ampules. Mg 3 GaN 3 was obtained as single crystals (space group R 3̅ m (No. 166), a = 3.3939(5) Å and c = 25.854(5) Å, Z = 3, R 1 = 0.0252, wR 2 = 0.0616 for 10 refined parameters, 264 diffraction data points). This double nitride consists of an uncharged three-dimensional network of MgN 4 and mixed (Mg/Ga)N 4 tetrahedra, which share common corners and edges. First-principles density functional theory (DFT) calculations predict Mg 3 GaN 3 to have a direct band gap of 3.0 eV, a value supported by soft X-ray spectroscopy measurements at the N K-edge. Eu 2+ -doped samples show yellow luminescence when irradiated with UV to blue light (λ max = 578 nm, full width at half maximum (fwhm) = 132 nm). Eu 2+ -doped samples of Mg 3 N 2 also show luminescence at room temperature when excited with ultraviolet (UV) to blue light. The maximum intensity of the emission band is found at 589 nm (fwhm = 145 nm).