Phase Evolution and Photoluminescence of Eu³⁺-Doped ZrO₂

Eu³⁺ doped ZrO₂ nanocrystals were prepared by decanoic acid-assisted hydrothermal method. X-ray diffraction, transmission electron microscope, Fourier transform infrared spectroscopy, Ultraviolet-visible diffuse reflection spectroscopy, and photoluminescence spectra were used to characterize the phase evolution, morphology, surface species, and optical properties of the samples. At low Eu³⁺ content, monoclinic ZrO₂ was achieved to show a rod-like morphology. With increasing the Eu³⁺ content, tetragonal ZrO₂ nanocrystals were obtained to show a ball-like shape. Decanoic acid molecules were decorated on the surfaces of ZrO₂ nanocrystals, which gave rise to a typical absorption centered at 300 nm. In addition to the characteristic emission of Eu³⁺, an intense broad emission was detected for pure and Eu³⁺-doped ZrO₂ nanocrystals under ultraviolet excitation, which is interpreted in terms of the F/F⁺ and/or AOD⁺ centers that are related with the oxygen vacancies.