Synthesis and strong red photoluminescence of europium oxide nanotubes and nanowires using carbon nanotubes as templates

Europium oxide nanotubes and nanowires have been successfully synthesized by a facile solvothermal method using carbon nanotubes (CNTs) as removable templates. The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, Fourier-transform infrared spectrophotometry, thermogravimetric and differential thermal analysis, and X-ray photoelectron spectroscopy. It is demonstrated that CNTs are fully coated with an amorphous Eu(OH)3 layer, which is ∼12 nm thick and almost continuous and uniform. After the Eu(OH)3/CNTs composites have been calcined at various temperatures, europium oxide nanotubes and nanowires are obtained by removing the CNT templates. The inner diameter of the europium oxide nanotubes is 40–60 nm, which is consistent with that of CNTs. Both nanotubes and nanowires have a narrow distribution of diameters. Furthermore, the photoluminescence properties of the europium oxide nanotubes and nanowires calcined at various temperatures have been systematically investigated. The results indicate that when the Eu(OH)3/CNTs composites were calcined at 600 °C for 6 h, the europium oxide nanotubes obtained have a strong red emission peak of Eu3+ ions at around 611 nm, due to the 5D0 → 7F2 forced electric dipole transition of Eu3+ ions. It is very interesting to discover that a few residual carbons doped in europium oxide nanotubes and many oxygen vacancies could promote the intensity of red emission peak of Eu3+ ions. In addition, europium oxide nanowires calcined at 1050 °C for 6 h also have a strong red emission peak due to many vacancies, such as oxygen vacancies, and defects formed on the surface of the nanowires and inside them.