A Simple, Efficient Synthetic Route to Sr₂Si₅N₈:Eu²⁺-Based Red Phosphors for White Light-Emitting Diodes

Abstract

This paper reports a simple, inexpensive, and high-yield synthetic route to Sr2Si5N8:Eu2+-based red nitridosilicate phosphors for white light-emitting diodes (LEDs). Through the chemical reaction of SrCO3, Eu2O3, and Si3N4 rather than the air-sensitive Sr, Eu, Si(NH)2, Sr3N2, and EuN powders, a complex phosphor consisting of Sr2Si5N8:Eu2+ (∼64 wt %) and Sr2SiO4:Eu2+ (∼36 wt %) were obtained by firing the powder mixture at 1600 °C under 0.5 MPa N2. The structural characterization, luminescence spectra, quantum efficiency, and thermal quenching of the synthesized phosphor were investigated and compared with those of Sr2Si5N8:Eu2+ prepared by the conventional method. It shows that the emission of the existing Sr2SiO4:Eu2+ is extremely low (about 0.04% of that of Sr2Si5N8:Eu2+) under the ultraviolet-light irradiation, and it is silent under the blue-light excitation (λ = 400−480 nm); therefore, the luminescence of the complex phosphor solely arises from Sr2Si5N8:Eu2+. The Sr2Si5N8:Eu2+-based phosphor is orange-red in color and emits strongly in the red region of 616−670 nm depending on the Eu2+ concentration when excited at λ = 450 nm. Furthermore, the Sr2Si5N8:Eu2+-based phosphor synthesized by this novel method shows equivalent optical properties, such as high emission intensity, high quantum efficiency, and very low thermal quenching, with those prepared by the conventional approaches, allowing it a promising red luminescent material for white LEDs.