Study on concentration quenching and energy transfer in Ln³⁺ (Ln = Tb, Tm, Eu) in Y₂O₃ nanocrystal powders

Nano-powders Y₂O₃ with various particle sizes and different doping concentrations of Ln(Ln = Tb, Tm, Eu) were prepared by using a combustion technique. The bulky powders doped with concentrations corresponding to nano-powders were obtained by annealing the nano-powders at high temperature. The emission spectra, XRD spectra and TEM were used in the present study. The concentration quenching of luminescent centers and energy transfer between luminescent centers in Y₂O₃:Ln nanocrystal powders were investigated. It was found that the behaviors of luminescence concentration quenching for ⁵D₄ → ⁷F₅:Tb³⁺ and ⁵D₀ → ⁷F₂:Eu³⁺ in nano-powders are similar to that in bulky powders. On the contrary, the quenching concentrations for ⁵D₃ → ⁷F₅:Tb³⁺ and ¹D₂ → ³H₄:Tm³⁺ are distinctly higher than that in bulk powders. This owes to the size confinement effect: the interface of nanocrystal particles can stop a portion of the energy transfer, which happens in the bulk ones, between luminescent centers. The size confinement effect can bring different influences to the different types of energy transfer. For instance, it will restrain the energy transfer (governed by electric dipole-dipole interaction) between the ions in long distances, and will hardly affect the energy transfer (governed by exchange interaction) between the ions locating at near intervals.