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Maak, Christian; Niklaus, Robin; Friedrich, Franziska; Mähringer, Andre; Schmidt, Peter J.; Schnick, Wolfgang (2017): Efficient Yellow-Orange Phosphor Lu4Ba2[Si9ON16]O:Eu2+ and Orange-Red Emitting Y4Ba2[Si9ON16]O:Eu2+: Two Oxonitridosilicate Oxides with Outstanding Structural Variety. In: Chemistry of Materials, Vol. 29, No. 19: pp. 8377-8384
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The oxonitridosilicate oxides Y4Ba2[Si9ON16]O:Eu2+ and Lu4Ba2[Si9ON16]O:Eu2+ have been synthesized starting from REF3, RE2O3 (RE = Y, Lu), BaH2, Si(NH)(2), and EuF3 in a radiofrequency furnace at 1550 degrees C. The crystal structures were solved and refined from single-crystal X-ray data supported with Rietveld refinement on X-ray powder diffraction data. Both compounds are isotypic and crystallize in monoclinic space group P2(1)/c (no. 14) with Z = 4 and a = 6.0756(2), b = 27.0606(9), c = 9.9471(3) angstrom, and beta = 91.0008(8)degrees for RE = Y and a = 6.0290(3), b = 26.7385(12), c = 9.8503(5) angstrom, and beta = 90.7270(30)degrees for RE = Lu. The unique crystal structure exhibits a three-dimensional network made up from Q(4)-type SiN4 and Q(3)-type SiON3 tetrahedra. Containing 4-fold bridging N-[4] atoms in star-shaped units [N-[4](SiN3)(4)] next to N-[3], N-[2], O-[1], and noncondensed oxide ions, the title compounds illustrate the vast structural variety in (oxo)nitridosilicates. Under excitation with UV to blue light, Y4Ba2[Si9ON16]O:Eu2+ shows emission in the orange-red spectral range (lambda(max) = 622 nm, full width at half-maximum (fwhm) approximate to 2875 cm(-1)). Yellow-orange emitting Lu4Ba2[Si9ON16]O:Eu2+ (lambda(max) = 586 nm, fwhm approximate to 2530 cm(-1)) exhibits high internal quantum efficiency (IQE) approximate to 85%. This makes Lu4Ba2[Si9ON16]O:Eu2+ a promising phosphor for low color rendering index (CRI) warm white phosphor converted light emitting diodes (pcLEDs).