Eu2+ photoluminescence in Al2O3 coatings obtained by plasma electrolytic oxidation

Al2O3 coatings doped with Eu ions were prepared by plasma electrolytic oxidation (PEO) process in electrolyte containing Eu2O3 particles. The analysis of the photoluminescence (PL) spectra showed that Eu3+ ions were reduced to Eu2+ during PEO in Al2O3 host. The most intense PL was obtained under excitation of 260 nm. PL emission spectra consist of two distinct broad bands with corresponding maxima at around 410 nm and 500 nm related to 4 f(6)5d(1) -> 4f(7) electronic transitions of Eu2+ ions. Sharp emission band in orange-red region of Eu3+ ions attributed to f-f transitions 5D(0) -> 7F(J) were not observed in PL emission spectra. Two PL bands in emission spectra indicate existence of two different Eu2+ sites in Al2O3 host. Relative ratio of these two broad bands depends on excitation wavelength as well as concentration of Eu2+ ions incorporated into Al2O3 coatings.