Crystalline grains of (Ba0.99Eu0.01)Al3Si4N9 were obtained from samples synthesized by heating mixtures of binary nitride powders at 2000°C and 0.85 MPa of N2 gas. The fundamental reflections of electron diffraction (ED) and X-ray diffraction (XRD) measured for some grains could be indexed with orthorhombic cell parameters: a=10.028(2) Å, b=53.353(9) Å, and c=5.9215(11) Å. Streaks and diffuse lines along the b axis were observed in the ED and XRD photographs, indicating stacking faults. A statistical average structure was analyzed using the intensity data of the fundamental reflections with the space group Fdd2. Local structure models were presented based on the average structure. Similar streaks and diffuse lines with fundamental reflections indexed with monoclinic cell parameters: a=5.8376(4) Å, b=26.6895(12) Å, c=5.8393(3) Å, and β=118.8428(15)°were also observed in the XRD oscillation photographs of another grain. The mixture of the grains having the orthorhombic and monoclinic fundamental structures emitted blue-green light with a peak wavelength of 500 nm and a full width at half-maximum (FWHM) of 65 nm under 400 nm excitation. The emission intensity measured at 300°C was 67.5% of the intensity measured at 25°C. A broad excitation band ranged from about 260 nm to 475 nm with maximum intensity at around 290 nm, and 60% of the intensity was obtained by excitation at 400 nm.
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