Figure 3.

(a) The excitation spectra of the 2 at % Tb-doped Y₂O₃ uncoated cubic (solid line), uncoated monoclinic (broken line), and SiO₂-coated monoclinic (blue line) nanoparticles monitored at 545 nm. The two bands around 280 and 310 nm are attributed to Tb³⁺ transitions. (b) Emission spectra of the same samples under 276 nm excitation. The appearing peaks correspond to Tb³⁺ ion transitions, with the most dominant being the one at 545 nm attributed to the ⁵D₄ → ⁷F₅ transition.