Controlled Hydrothermal Synthesis of Zirconium Oxide Nanostructures and Their Optical Properties

Zirconium oxide (ZrO2 or zirconia) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of various zirconia nanostructures at different synthesis conditions. X-ray diffraction examination demonstrates that the as-synthesized zirconia is of pure monoclinic phase (m-ZrO2). High resolution transmission electron microscopy (HRTEM) further confirms the high crystalline feature of the m-ZrO2 nanostructures. X-ray photoelectron spectroscopy (XPS) core-level spectra of Zr 3d and O 1s for the ZrO2 nanostructures have been studied to understand further the electronic states and chemical environment of the Zr and O atoms in ZrO2 for different synthesis conditions. XPS results also indicate the existence of oxygen defects and zirconia suboxides which affect the structural and optical properties of zirconia nanostructures. The nanostructures show UV−vis absorption band around 290 nm at room temperature. The band gap energy is determined, in the range of 2.5−3.8 eV for zirconia nanostructures synthesized at various conditions. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of zirconia nanostructures at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancy in the material.