One-Pot Synthesis of Single-Source Precursors for Nanocrystalline LED Phosphors M2Si5N8:Eu2+ (M = Sr, Ba)

Abstract

Highly efficient red-emitting nitridosilicate phosphors Sr2Si5N8:Eu2+ and Ba1.5Sr0.5Si5N8:Eu2+ (doping level 1 %) applicable to phosphor converted pc-LEDs were synthesized in nanocrystalline form at low temperatures employing a novel single-source precursor approach. Synthesis starts from nanocrystalline silicon and uses mixed metal amides M(NH2)2 with M = Sr, Ba, Eu as reactive intermediates. In a second approach, a single-source precursor mixture obtained from a one-pot reaction of the corresponding elements (Sr/Ba, Eu, Si) was obtained in supercritical ammonia. Thermoanalytical in situ investigations gain a deeper insight into the degradation mechanism of the mixed metal amide precursors and revealed the onset for the formation of the 2-5-8 phosphor materials at temperatures slightly above 900 °C. Formation of the products is complete below 1400 °C. Under these conditions, the nitridosilicate phosphors form spherically shaped particles with crystallites of 200 nm in size. Spherical particles are desira...