Inverse-Tunable Red Luminescence and Electronic Properties of Nitridoberylloaluminates Sr 2-x Ba x [BeAl 3 N 5 ]:Eu 2+ (x=0-2).

The nitridoberylloaluminate Ba 2 [BeAl 3 N 5 ]:Eu 2+ and solid solutions Sr 2-x Ba x [BeAl 3 N 5 ]:Eu 2+ (x=0.5, 1.0, 1.5) were synthesized in a hot isostatic press (HIP) under 50 MPa N 2 atmosphere at 1200 °C. Ba 2 [BeAl 3 N 5 ]:Eu 2+ crystallizes in triclinic space group P 1 ‾ (no. 2) (Z=2, a=6.1869(10), b=7.1736(13), c=8.0391(14) Å, α=102.754(8), β=112.032(6), γ=104.765(7)°), which was determined from single-crystal X-ray diffraction data. The lattice parameters of the solid solution series have been obtained from Rietveld refinements and show a nearly linear dependence on the atomic ratio Sr : Ba. The electronic properties and the band gaps of M 2 [BeAl 3 N 5 ] (M=Sr, Ba) have been investigated by a combination of soft X-ray spectroscopy and density functional theory (DFT) calculations. Upon irradiation with blue light (440-450 nm), the nitridoberylloaluminates exhibit intense orange to red luminescence, which can be tuned between 610 and 656 nm (fwhm=1922-2025 cm -1 (72-87 nm)). In contrast to the usual trend, the substitution of the smaller Sr 2+ by larger Ba 2+ leads to an inverse-tunable luminescence to higher wavelengths. Low-temperature luminescence measurements have been performed to exclude anomalous emission.