Understanding the β –K ₂ CO ₃ -Type Na(Na _0.5 Sc _0.5 )BO ₃ :Ce ₃ + Phosphor

Abstract

A Na(Na 0.5 Sc 0.5 )BO 3 :Ce 3+ phosphor in the β –K 2 CO 3 -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 Ce 3+ having a significant site preference for the eight-coordinated Na + crystallographic site rather than the smaller six-coordinated Na + /Sc 3+ site. Analyzing the local crystal structure through a combined computational and spectroscopic analysis showed that the substitution of Ce 3+ 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.