Improvement of the Water Resistance of a Narrow-Band Red-Emitting SrLiAl3N4:Eu2+ Phosphor Synthesized under High Isostatic Pressure through Coating with an Organosilica Layer

A SrLiAl3N4:Eu2+ (SLA) red phosphor prepared through a high‐pressure solid‐state reaction was coated with an organosilica layer with a thickness of 400–600 nm to improve its water resistance. The observed 4f65d→4f7 transition bands are thought to result from the existence of Eu2+ at two different Sr2+ sites. Luminescence spectra at 10 K revealed two zero‐phonon lines at 15377 (for Eu(Sr1)) and 15780 cm−1 (for Eu(Sr2)). The phosphor exhibited stable red emission under high pressure up to 312 kbar. The configurational coordinate diagram gave a theoretical explanation for the Eu2+/3+ result. The coated samples showed excellent moisture resistance while retaining an external quantum efficiency (EQE) of 70 % of their initial EQE after aging for 5 days under harsh conditions. White‐light‐emitting diodes of the SLA red phosphor and a commercial Y3Al5O12:Ce3+ yellow phosphor on a blue InGaN chip showed high color rendition (CRI=89, R9=69) and a low correlated color temperature of 2406 K. Stay dry and warm in this coat: The red‐emitting phosphor SrLiAl3N4:Eu2+ has superior luminescence properties but is water‐sensitive and generally synthesized from metal‐hydride precursors. These limitations were overcome by the use of a high‐pressure synthetic method and the application of an organosilica coating. The resulting material with enhanced optical properties was used to make high‐performance warm‐white‐light‐emitting diodes.