Phase Transformation and Photoluminescence Properties of Nanocrystalline ZrO2Powders Prepared via the Pechini-type Sol−Gel Process

Nanocrystalline ZrO 2 fine powders were prepared via the Pechini-type sol−gel process followed by annealing from 500 to 1000 °C. The obtained ZrO 2 samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), and photoluminescence spectra (PL), respectively. The phase transition process from tetragonal (T) to monoclinic (M) was observed for the nanocrystalline ZrO 2 powders in the annealing process, accompanied by the change of their photoluminescence properties. The 500 °C annealed ZrO 2 powder with tetragonal structure shows an intense whitish blue emission (λ max = 425 nm) with a wide range of excitation (230−400 nm). This emission decreased in intensity after being annealed at 600 °C (T + M-ZrO 2 ) and disappeared at 700 (T + M-ZrO 2 ), 800 (T + M-ZrO 2 ), and 900 °C (M-ZrO 2 ). After further annealing at 1000 °C (M-ZrO 2 ), a strong blue-green emission appeared again (λ max = 470 nm). Based on spectral analysis and EPR results, the whitish blue emission (425 nm) and blue-green emission (470 nm) can be ascribed to interstitial carbon impurities (C i ) in the tetragonal ZrO 2 and oxygen vacancies (V O ) in the monoclinic ZrO 2, respectively.