Zirconia films formed by plasma electrolytic oxidation: Photoluminescent and photocatalytic properties

• Zirconia films are formed by plasma electrolytic oxidation (PEO) of zirconium foils.
• Well-resolved photoluminescence (PL) bands occur in the range from 300 nm to 600 nm.
• PL bands originate from optical transition of oxygen vacancy defects in zirconia.
• PL intensity increases with duration of PEO.
• Photocatalytic activity of zirconia films increases with duration of PEO.

In this paper, we have investigated photoluminescence and photocatalytic properties of zirconia films formed by plasma electrolytic oxidation (PEO) of zirconium foil in 0.1 M water solution of citric acid. Zirconia films with diverse morphology and phase structure are formed varying the time of PEO process. Characterization by atomic force microscopy and X-ray diffraction shows that obtained zirconia films mostly consist of monoclinic ZrO2 phase, while corresponding roughness and crystallite size increases with PEO time. Diffuse reflectance spectroscopy has shown that zirconia films have a broad absorption band in the range from 200 nm to 330 nm, indicating that zirconia films could be used as a photocatalyst using ultraviolet radiation. Strong photoluminescence bands are present in spectra featuring four distinct peaks in the 300–600 nm range. The peaks are centered at about 418 nm, 440 nm, 464 nm, and 495 nm. Apparent increase of photoluminescence intensity with PEO time is related to an increase of oxygen vacancy defects in zirconia films formed during the process. Also, higher concentration of oxygen vacancy defects in zirconia films result in higher photocatalytic activity.