Illuminating Nitridoberylloaluminates: The Highly Efficient Red-Emitting Phosphor Sr₂[BeAl₃N₅]:Eu²⁺

The nitridoberylloaluminate Sr2[BeAl3N5]:Eu2+ was obtained through reaction of the binary nitrides in a hot isostatic press (HIP) under a pressure of 50 MPa N2 and a temperature of 1400 °C. The crystal structure was solved and refined from single-crystal X-ray diffraction data (P1̅ (no. 2), Z = 2, a = 6.061(2), b = 6.982(3), c = 7.872(4) Å, α = 102.22(3), β = 112.62(2), and γ = 104.02(2)°). The crystal structure of Sr2[BeAl3N5]:Eu2+ is made up out of a network of vertex- and edge-sharing AlN4 tetrahedra and trigonal-planar BeN3 units. The negative charge is compensated by Sr2+ ions occupying three crystallographic sites. Sr2+ ions are coordinated by seven and eight N atoms, respectively. After irradiation of Eu2+ doped samples with blue light (440–450 nm), strong red luminescence (emission maximum at ≈612 nm; full width at half-maximum (fwhm) 65–73 nm (1715–1966 cm–1) is observed. Until now, Sr2[BeAl3N5]:Eu2+ is the only member of a compound class containing only beryllium and aluminum as network building atoms in a nitride, contributing to the range of red-emitting phosphors such as Sr[LiAl3N4]:Eu2+ (SLA), Sr[Li2Al2O2N2]:Eu2+ (SALON), Sr4[LiAl11N14]:Eu2+, or Sr[Mg3SiN4]:Eu2+ (SMS).