Luminescent Properties of Pure Cubic Phase Y₂O₃/Eu³⁺ Nanotubes/Nanowires Prepared by a Hydrothermal Method

One-dimensional pure cubic Y₂O₃/Eu³⁺ nanocrystals (NCs) were synthesized by a hydrothermal method at various temperatures. The NCs prepared at 130 °C yielded nanotubes (NTs) with wall thickness of 5−10 nm and outer diameter of 20−40 nm. The NCs prepared at 170 and 180 °C yielded nanowires (NWs) with diameters of ∼100 and ∼300 nm, respectively. Their luminescent properties, including electronic transition processes, local environments surrounding Eu³⁺ ions, electron−phonon coupling, and UV light irradiation induced spectral changes have been systematically studied and compared. The results indicate that the Y₂O₃/Eu³⁺ NTs and NWs have strong red ⁵D₀−⁷F₂ transitions. The fluorescence lifetime of ⁵D₁−⁷F₁ hardly changes in different samples, while that of ⁵D₀−⁷F₂ decreases a small amount in Y₂O₃/Eu³⁺ NTs. The ⁵D₀−⁷F₂ lines originate from the emissions of Eu³⁺ ions occupying one C₂ site, like that in the bulk powders. The phonon sideline with a frequency shift of 40−50 cm^-1 appears at the low-energy side of the ⁷F₀−⁵D₀ zero phonon line. The relative intensity of the sideline to zero phonon line increases by varying from NTs to NWs, and the spectral position of the phonon sideline shifts red. The UV light irradiation induced spectral change in the charge-transfer band was studied. The results indicate that the spectral change is dependent on sample size and is wavelength selective. A detailed model was proposed to explain the light-induced spectral change.