Luminescent Properties of Rare Earth Fully Activated Apatites, LiRE₉(SiO₄)₆O₂ (RE = Ce, Eu, and Tb): Site Selective Crystal Field Effect

다국어 초록 (Multilingual Abstract)

<P>Novel LiCe9(SiO4)(6)O-2 and LiTb9(SiO4)(6)O-2 compounds have been successfully synthesized, and the site selectivity and occupancy of activator ions have been estimated including LiEu9(SiO4)(6)O-2 compound. The rare earth (RE) fully occupied compounds, as well as the RE partially occupied congeners are required for the assessment of site selectivity of RE (activator) ions in apatite-type compounds. The splitting energies of the 6H and 4F Wycoff positions of LiRE9(SiO4)(6)O-2 (RE = Ce, Eu, and Tb) compounds are calculated based on crystal field theory: Delta E-Ce(6H) = 3849.3 cm(-1), Delta E-Ce(4F) = 4228.1 cm(-1), Delta E-Eu(6H) = 3870.0 cm(-1), Delta E-Eu(4F) = 4092.8 cm(-1), Delta E-Tb(6H) = 3637.6 cm(-1), Delta E-Tb(4F) = 4396.1 cm(-1), indicating that the splitting energy for the 4F site is larger than that for the 6H site in all compounds; thus the absorption energy is higher for the 6H site. In apatite-type LiRE9(SiO4)(6)O-2 (RE = Ce, Eu, and Tb) compounds, the Ce3+ ions predominantly occupy the 4F site associated with the absorption band around 300 nm at lower Ce3+ concentration, and then enter the 6H site associated the absorption band around 245 nm. For the Eu3+-doped compounds, the 4F site and 6H site are mixed within the charge transfer band (CTB) between 220 and 350 nm. Eu3+ ions initially preferentially occupy the 6H site (around 290 nm) at lower Eu3+ concentration and subsequently enter the 4F site (around 320 nm) with increasing Eu3+ concentration. For the Tb3+-doped compounds, the absorption due to the two different sites is mixed within f-d absorption band between 200 and 300 nm. At lower Tb3+ concentration, the Tb3+ ions enter favorably 6H site around 240 nm and then enter 4F site around 270 nm. These compounds may provide a platform for modeling a new phosphor and application in the solid-state lighting field.</P>