Yellow single crystals of aluminum silicon nitrides containing strontium and europium were prepared by heating starting mixtures of Sr3N2, Si3N4, AlN, and EuN at 2050 degrees C and 0.85MPa of N-2 for 8hours. Single-crystal X-ray diffraction revealed that prismatic crystals 20-100m in size were Sr0.31Al0.62Si11.38N16:Eu (trigonal, a=7.7937(2) angstrom, c=5.6519(2)angstrom, space group P31c), which are isotypic with Sr--SiAlON, Srm/2Alm+nSi12-m-nN16-nOn, with m=0.62 and n=0. The Eu2+ content was approximately 1at.% of Sr contained in the framework of corner-sharing (Al/Si)N-4 tetrahedra with an occupancy of 0.154(2). Block-shaped crystals with a side length of 50-300m were a new polytypoid of Sr--SiAlON, Sr2.97Eu0.03Al6Si24N40. Streak lines were observed in the direction of the c* axis in the X-ray oscillation photographs, indicating stacking faults of the structure. The fundamental X-ray reflections were indexed with a hexagonal cell (a=7.9489(3)angstrom, c=14.3941(6)angstrom). The structure was analyzed with a model of space group P6 in which one of the six Al/Si sites was statistically split into two sites with occupancies of 0.673(5) and 0.227(5). The atomic arrangements in the layers of the structure were similar to those of Sr--SiAlON, but the stacking sequences of the layers were different. The peak wavelengths and full widths at half maximum of emission spectra measured for the single crystals of Sr0.31Al0.62Si11.38N16:Eu and Sr2.97Eu0.03Al6Si24N40 were 583nm and 87nm, and 584nm and 91nm, respectively, under 400nm wavelength light excitation at room temperature.