Cost-Effective β-SiAlON/Yb2+ Green Phosphors: From Synthesis to Characterization of Optical, Crystallographic, and Microstructural Properties

Abstract

β-SiAlON phosphors have attracted attention in light-emitting diodes (LEDs) over the last decade due to their outstanding properties, including low energy consumption, long service life, and high impact. Here, a mixture consisting of kaolin (Al₂O₃.2SiO₂·2H₂O), silica (SiO₂), active carbon (C), Yb₂O₃ (0.01 ≤ x ≤ 0.07 mol.%), and a Li₂CO₃ activator was sintered in two steps (1050°C for 1 h followed by 1500°C for 6 h) under N₂ atmosphere with 0.75 L/min through carbothermal reduction and nitridation (CRN). Based on the x-ray diffraction (XRD) and Rietveld refinement analyses of the produced specimens, Yb²⁺-doped β-SiAlON phosphors were obtained as a single phase. Microstructural observations of β-SiAlON phosphors were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Accordingly, the β-SiAlON phase was successfully activated by the Yb rare-earth cation. In addition, β-SiAlON powders were needle-like and equiaxed nucleoid hexagonal or short-grained. The photoluminescence (PL) analysis revealed that Yb²⁺/β-SiAlON phosphors exhibited a broad emission peak in the green-to-greenish-yellow range (520–570 nm), with a maximum at 543 nm. Also, the Commission Internationale de l’éclairage (CIE) x and y coordinates specified that all β-SiAlON:Yb²⁺ phosphors were within the green emission region. Our approach, presented herein, enables the synthesis of low-cost monophase Yb²⁺/β-SiAlON phosphors from economical kaolin raw material, rather than high-purity powders, via the CRN production method.

Graphical Abstract