Formation and photoluminescence of Eu3+ doped zirconia coatings formed by plasma electrolytic oxidation

Eu3+ doped ZrO2 coatings were formed by plasma electrolytic oxidation of zirconium in electrolyte containing Eu2O3 powder. The content of Eu in coatings increases with the time of PEO process. The coatings are crystallized and mostly composed of monoclinic ZrO2 phase. Photoluminescence (PL) emission spectra of Eu3+ doped ZrO2 coatings feature two distinct regions. The first region is related to ZrO2 PL band with a maximum positioned at about 490 nm, while the second region in the orange-red part of the spectrum shows sharp emission bands which are related to f-f transitions of Eu3+ from excited level 5D0 to lower levels 7FJ (J=0, 1, 2, 3, and 4). Excitation PL spectra of Eu3+ doped ZrO2 coatings monitored at 480 nm feature a broad PL band with spectral maximum at about 280 nm. In contrast, the excitation PL spectra monitored at the wavelength of the most intense peak in emission PL spectra can be divided into two regions: (a) the broad band region from 240 nm to 350 nm with a maximum at about 250 nm, which is associated with the electron transfer transition from 2p orbital of O2− ions to 4f orbital of Eu3+ ions and (b) the region in the range from 350 nm to 550 nm with the series of sharp peaks, which correspond to direct excitation of the Eu3+ ground state 7F0 into higher levels of the 4f-manifold.