Structural origin of blue luminescence in Ce-doped Ba2Y5B5O17 and Ba3Y2B6O15 with multiple cation sites and occupational disorder

Abstract

It was recently reported that Ce-doped Ba2Y5B5O17 and Ba3Y2B6O15 compounds displayed efficient and thermally stable blue luminescence under ultraviolet (UV) or near-UV excitation. However, the site occupations of Ce3+ are not yet clarified due to existence of multiple cation sites with occupational disorder. Herein, combined density functional theory (DFT) and multiconfigurational ab initio calculations at the spin-orbit effect were performed to gain insights into structural origin of Ce3+ luminescence. The results show that the blue emission in Ce-doped Ba2Y5B5O17 originates mostly from Ce3+ located at the disordered Y2/Ba2 site while, in Ce-doped Ba3Y2B6O15, it comes from Ce3+ at the Y2 and Y3 sites with nearly identical probabilities. The Ce3+ 4f ground-state and the lowest 5d excited-state levels within the host band gaps are compared and discussed in association with local structures and luminescence thermal stabilities. This investigation is expected to enhance our understanding of lanthanide luminescence in cation-disordered phosphors.