Study on UV excitation spectra of Eu³⁺ or Tb³⁺ doped Y₂O₃ nanomaterials

Y₂O₃: Ln nanocrystals with different Ln³⁺ (Ln = Eu or Tb) doping concentrations and average sizes were prepared by chemical self-combustion. And the bulk materials of corresponding doping concentrations were obtained by annealing at high temperature. The emission spectra, excitation spectra and X-ray diffraction spectra of Y₂O₃: Ln nanocrystals and bulk materials were measured. The research indicated that under the effect of quantum confinement effect and surface effect, the Y₂O₃: Eu charge transfer band red-shifted clearly while the particle size decreased. Furthermore, the charge transfer band of the small size particles (8 nm) clearly broadened towards the long wavelength, this was attributed to the increase of the amount of Eu³⁺ ions existing in low crystallization degree environment close to the surface. The study also indicated that the shape of excitation peaks (bands) corresponding to the 4f5d transition absorption of Tb³⁺ in the excitation spectra of Y₂O₃: Tb nanocrystals changed a lot with the variety of the particle size. This is because that the Tb³⁺ ions exist in two very different local environments:the low crystallization degree environment close to the surface and the high crystallization degree environment inner the particles. The absorption peaks of 4f5d transition were diffe-rent in the two environments. The Tb³⁺ ions ratio in the two environments changs with the variety of the particle size. So the intensity of corresponding excitation peaks (bands) changed and the shapes of the excitation spectra changed. By comparing the excitation spectra of different doping concentrations, it can be found that with the increase of Tb³⁺ (or EU³⁺) concentrations, the relative strength of the Y₂O₃ exciton transition absorption excitation peak to the 4f5d transition (or charge transfer band) excitation peak decreased. The excitation efficiency of Y₂O₃ exciton absorption band is very low when the doping concentrations of the luminescent centers were higher. But the excitation efficiency of Y₂O₃ exciton absorption band increased when the doping concentrations were quite low.