Ce ³⁺ ‐Activated Lithium Rare‐Earth Oxonitridolithosilicates: A New Class of LED Phosphors with Similarities to Garnets

Green‐emitting Ce 3+ ‐activated solid‐state phosphors are in the key focus of the development of next‐generation phosphor‐converted LEDs (pc‐LEDs). With the first representatives of the substance class of lithium rare‐earth oxonitridolithosilicates Li 9 RE Si 4 N 4 O 8 ( RE = Y, La, Gd, Dy, Yb, Lu), access has been unlocked to a whole new family of promising potential host materials. Synthesized with a high‐temperature solid‐state approach in tantalum ampoules, Li 9 RE Si 4 N 4 O 8 crystallizes in the tetragonal space group P 4 /n (no. 85) in a hitherto unknown structure type. The reported compounds have been structurally characterized by single‐crystal (SC) and powder X‐ray diffraction (PXRD). Phase stability has been analyzed by high‐temperature PXRD and thermogravimetry, and the morphology and element content by scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDX). The compounds prove to be excellent hosts for Ce 3+ ions, yielding highly efficient phosphor materials with luminescence maxima in the green spectral region ( λ max_Y = 544 nm, FWHM Y = 0.51 eV; λ max_Gd = 536 nm, FWHM Gd = 0.51 eV) and high internal quantum yields. As both the emission maxima and band widths meet the values for the Ce 3+ ‐activated garnets ( RE 3 M 5 O 12 ( RE = Y, Lu; M = Al, Ga)), the temperature‐dependent photoluminescence properties of Ce 3+ ‐activated Li 9 RE Si 4 N 4 O 8, as well as the general applicability in a prototype LED are compared to these state‐of‐the‐art green phosphors, demonstrating competitiveness.