Down-conversion photoluminescence of ZrO2:Er3+ coatings formed by plasma electrolytic oxidation

Plasma electrolytic oxidation of zirconium in alkaline solution containing Er2O3 powder was used for preparation of ZrO2:Er3+ coatings. Photoluminescence (PL) emission spectra of ZrO2:Er3+ excited by ultraviolet irradiation are composed of broad PL band associated with ZrO2 host and sharp bands corresponding to f-f transitions of Er3+. The strongest green PL emission band of Er3+ in the range from 540 nm to 580 nm is assigned to 4S3/2 → 4I15/2 transition. The PL excitation spectra of ZrO2:Er3+ characterize broad band from 250 nm to 350 nm associated with charge transfer state of Er3+ and the series of peaks in the range from 350 nm to 530 nm which are associated with 4f transitions of the Er3+ from ground state 4I15/2 to higher levels. Obtained results allowed the identification of down-conversion PL mechanism.