Tunable Red Luminescence in Nitridomagnesoaluminates α-Sr2[MgAl5N7]:Eu2+, β-Sr2[MgAl5N7]:Eu2+, and Sr8[LiMg2Al21N28]:Eu2+

Red-emitting phosphors with the general sum formula Sr8[Li(2–0.5x)MgxAl(22–0.5x)N28]:Eu2+ for application in warm-white illumination grade light emitting diodes were obtained by reacting the metals, hydrides, and nitrides in molybdenum crucibles in a hot isostatic press. Upon irradiation with blue light (440 nm), the materials exhibit red luminescence (emission maximum: 633–665 nm; full width at half-maximum (fwhm): 1736–1964 cm–1, 78–82 nm) tunable by adjusting the compositional variable x (here, 2 and 4) as well as the activator concentration (here, 0.075–1 atom-% Eu2+). The materials show promising thermal behavior of the emission with relative quantum efficiencies, compared to room temperature, of 66% (x = 0) and 84% (x = 2) at 200 °C. α-Sr8[Li(2–0.5x)MgxAl(22–0.5x)N28]:Eu2+ (x = 2 and 4) crystallizes isotypically with Sr4[LiAl11N14]:Eu2+ in the orthorhombic space group Pnnm (no. 58) with unit cell parameters a = 10.51818(5)–10.54878(6), b = 10.44513(5)–10.48253(6), and c = 3.25704(1)–3.272752(15) A. ...