Synthesis of RE6–xCa1.5xSi11N20O (RE = Yb, Lu; x ≈ 2.2) with Lu6–xCa1.5xSi11N20O:Ce3+ Offering Interesting Spectral Properties for Yellow-Emitting Phosphors in 1pcLEDs

Abstract

The oxonitridosilicates RE6–xCa1.5xSi11N20O (RE = Yb, Lu; x ≈ 2.2) were synthesized starting from REF3, CaH2, and ”Si(NH)2” in a radiofrequency furnace at 1600 or 1400 °C, respectively. The crystal structure was solved and refined from single-crystal X-ray diffraction data of dark red Yb6–xCa1.5xSi11N20O crystals in the trigonal space group P31c (no. 159) with a = 9.8281(10), c = 10.5968(13) Å and Z = 2. The structure represents a filled variant of the Er6Si11N20O structure type, in which the charge difference caused by substitution of trivalent Yb3+ with bivalent Ca2+ is balanced by occupation of an additional third cation site. Synthesis of Lu6–xCa1.5xSi11N20O:Ce3+ resulted in a yellow powder with yellow luminescence. Powder X-ray data were analyzed by Rietveld refinement based on the crystal data obtained from Yb6–xCa1.5xSi11N20O. The Ce3+ doped compound exhibits a broad emission (fwhm ≈ 168 nm/≈ 5100 cm–1) with a maximum at λem ≈ 565 nm. The emission extends more in the red spectral range compared to YAG:Ce3+, thus making it an interesting phosphor for warm-white single phosphor converted light-emitting diodes (1pcLED) with an improved color rendering index.