Synthesis of a Multinary Nitride, Eu-Doped CaAlSiN3, from Alloy at Low Temperatures

Abstract

A multinary nitride, Eu-doped CaAlSiN3, which had previously been synthesized at 1600–1800 °C as a red-emiting phosphor material, was obtained at 500–800 °C via the reaction of a CaAlSi alloy with a low concentration of Eu (composition Ca0.992Eu0.008AlSi) in ammonia in the present study. In supercritical ammonia (100 MPa), CaAlSiN3 was formed at temperatures ≥ 500 °C both with and without the addition of sodium amide. The addition of sodium amide significantly facilitated the synthesis and prevented the presence of unreacted silicon, which could be due to the formation of sodium ammonometallates as intermediates in the presence of sodium amide. CaAlSiN3 was synthesized even in an atmospheric ammonia flow, but the crystallinity of the product was rather low. Evidence suggested that CaAlSiN3 was insoluble in the pressurized sodium amide−ammonia medium under the present conditions, and the prolonged reaction of the alloy in ammonia at the CaAlSiN3-forming temperatures (500–800 °C) did not result in an effect...