4f5d transition and energy transfer of Tb³⁺ doped Y₂O₃ nanocrystalline

Nanocrystal powders of Y₂O₃:Tb with different Tb³⁺ doping concentrations and average sizes were prepared by chemical self-combustion, and the bulk samples of corresponding concentrations were also obtained by annealing nanomaterials at high temperatures. The emission spectra, excitation spectrum, X-ray diffraction, transmission electron microscopy images and fluorescence decay curves of Y₂O₃:Tb nanomaterials and bulk materials were measured. Then the 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions in Y₂O₃:Tb nanocrystal powders was studied. Great difference in the excitation spectral line shapes for different sized Y₂O₃:Tb nanocrystal powders was observed. The change of excitation spectral line shapes is because that the Tb³⁺ ions exist in two very different local environments including the low crystallization degree of close surface and the high crystallization degree inside the particles. The absorption peaks of 4f5d transition are different in these two environments. Also the ⁵D₃ → ⁵D₄ and ⁵D₄ → ⁵ D₄ energy transfer and luminescence concentration quenching caused by energy transfer were investigated. The (⁵D₃, ⁷ F₆) → (⁵ D₄, ⁷ F₀) energy transfer is caused by interaction of electric dipoles, which is greatly affected by the quantum confinement effect. The concentration quenching of ⁵D₄ → ⁷F₅ luminescence is resulted by the energy transfer of exchange interaction among ⁵D₄ (Tb) energy levels of different Tb³⁺ ions. The quantum confinement showed little influence on this type of energy transfer.