Short Process for Preparing Long-Lasting SrAl₂O₄- and CaAl₂O₄-based Phosphors by Spark Plasma Sintering

Long-lasting phosphors, SrAl2O4: Eu, Dy and CaAl2O4: Eu, Nd, have been prepared by a short process using the spark plasma sintering method. The raw oxide powders were mixed for 5 min using a high-energy mill. Subsequently, solid-state reaction and sintering were simultaneously performed for approximately 20 min using a spark plasma sintering apparatus. The sintering temperatures were set to 1150–1500°C for SrAl2O4: Eu, Dy and 1100–1400°C for CaAl2O4: Eu, Nd. The X-ray diffraction patterns showed that a sintering temperature of 1400°C or higher was required for single-phase synthesis of SrAl2O4: Eu, Dy, while a sintering temperature of 1200°C was suitable for synthesis of CaAl2O4: Eu, Nd. The sintered SrAl2O4: Eu, Dy and CaAl2O4: Eu, Nd phosphors exhibited bright green and blue emission by ultraviolet irradiation, respectively, and they showed afterglow properties. In particular, SrAl2O4: Eu, Dy prepared at 1500°C and CaAl2O4: Eu, Nd prepared at 1200°C showed good performance in terms of both the initial emission intensity and afterglow properties. Thus, sintered long-lasting SrAl2O4: Eu, Dy and CaAl2O4: Eu, Nd phosphors can be prepared by a short process using spark plasma sintering if the sintering temperatures are properly selected.