Understanding the β–K2CO3-Type Na(Na0.5Sc0.5)BO3:Ce3 + Phosphor

Abstract

A Na(Na0.5Sc0.5)BO3:Ce3+ phosphor in the β–K2CO3-type crystal structure was developed by identifying orthoborate substitutional derivatives with distinct crystal and electronic structure and high structural rigidity. Crystal structure and compositional analysis after the high-temperature synthesis of the target phase confirmed the product’s phase purity. Photoluminescence spectroscopy revealed a bright blue emission centered at 420 nm under 340 nm excitation. Computational modeling indicated that the optical properties stem from Ce3+ having a significant site preference for the eight-coordinated Na+ crystallographic site rather than the smaller six-coordinated Na+/Sc3+ site. Analyzing the local crystal structure through a combined computational and spectroscopic analysis showed that the substitution of Ce3+ on the normally eight-coordinated site causes an unexpected evolution of the crystal structure resulting in a nine-coordinated rare-earth position leading to the blue emission. These results highlight the importance of using a combined computational and experimental evaluation to develop new phosphors and understand their ensuing complex optical properties.