Narrow-Band Yellow-Orange Emitting La_3–xCa_1.5xSi₆N₁₁:Eu²⁺ (x ≈ 0.77): A Promising Phosphor for Next-Generation Amber pcLEDs

The nitridosilicate La3–xCa1.5xSi6N11:Eu2+ (x ≈ 0.77) was synthesized in a radiofrequency furnace starting from LaF3, La(NH2)3, CaH2, Si(NH)2, and EuF3. The crystal structure was solved and refined from single-crystal X-ray data in the tetragonal space group P4bm (no. 100) with a = 10.1142(6), c = 4.8988(3) Å, and Z = 2. Thereby, the so far unknown charge balance mechanism in the system (La,Ca)3Si6N11, which is necessary as bivalent Ca2+ substitutes trivalent La3+, was clarified. Accordingly, charge balance is achieved by incorporation of Ca2+ on three cation sites, including an additional third site compared to the homeotypic La3Si6N11 structure type. The results are supported by Rietveld refinement on powder X-ray diffraction data as well as energy-dispersive X-ray spectroscopy. Fourier transform infrared spectroscopy indicates absence of N–H bonds. An optical band gap of ≈ 4.0 eV was determined using UV/vis reflectance spectroscopy. The Eu2+ doped compound exhibits a remarkably narrow emission in the yellow-orange spectral range (λem ≈ 587 nm, fwhm ≈ 60 nm/1700 cm–1). Because of the intriguing yellow-orange luminescence, La3–xCa1.5xSi6N11:Eu2+ (x ≈ 0.77) is a promising candidate for application in next-generation amber phosphor-converted light emitting diodes.