(618c) Role of Ce in Manipulating Tb Luminescence in Y2Zr2O7 Nanoparticles

Y₂Zr₂O₇ （YZO） has been reported to be a good host material for rare earth phosphor emitting luminescence due to its stable structural and thermal properties. Meanwhile, Tb is opted as the dopant to create strong green emission in the YZO lattice as the Tb emission can be sensitized by Ce. Herein, a two-step synthesis method, co-precipitation and molten salt, was employed to prepare the YZO NPs. First, 2 mol% Tb doped YZO NPs were synthesized and used as reference for these luminescence studies as the YZO:Tb³⁺ (2 mol%) NPs have demonstrated strong Tb³⁺ luminescence with long lifetimes (~998 μs), indicating efficient radiative relaxation. Contrary to the expected photoresponse, the PL results show that even a trace amount of Ce in the YZO:Tb lattice quenches the Tb luminescence. To identify the quenching mechanism (oxidation state/local symmetry), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) was performed on these NPs and it was found the Ce⁴⁺ ion in the YZO lattice drives the Tb oxidation state to non-luminescent 4+ state. Next, Eu³⁺ was employed into YZO NPs to replace Tb to study the change of local symmetry with Ce concentration by calculating the PL intensity ratio of magnetic dipole and electronic dipole. The asymmetry ratio indicates an increasing symmetry level with introducing Ce into the system due to the incorporation of higher concentrations of lattice oxygen. As such, careful consideration of the effect of dopant ions on local symmetry and dopant oxidation states is needed for high efficiency phosphors.