Photoluminescence properties of Er ³⁺ /Yb ³⁺ doped ZrO <inf>2</inf> coatings formed by plasma electrolytic oxidation

Abstract

In the present work, down- and up-conversion photoluminescence properties of Er 3+ /Yb 3+ doped ZrO 2 coatings formed by plasma electrolytic oxidation of zirconium in electrolyte containing Er 2 O 3 and Yb 2 O 3 particles were investigated. Down-conversion PL analysis shows that emission spectra of ZrO 2 :Er 3+ /Yb 3+ coatings excited with 280 nm radiation are composed of broad PL band related to ZrO 2 host and bands assigned to f-f transitions of Er 3+ . The main PL emission bands of Er 3+ at around 548 nm and 560 nm are related to 4 S 3/2 → 4 I 15/2 transition. PL excitation spectra monitored at 548 nm feature broad band in the region from 250 nm to 350 nm which is associated with the electron transfer transition from 2p orbital of O 2− to 4f orbital of Er 3+ and transitions of ZrO 2 . On the other hand, bands in PL excitation spectra ranging from 350 nm to 535 nm are related to 4f transitions of the Er 3+ from the ground state 4 I 15/2 to higher energy levels. Down-conversion PL intensity decreases with increasing concentration of Yb 3+ in coating due to energy transfer from Er 3+ to Yb 3+ . ZrO 2 :Er 3+ /Yb 3+ coatings show intense green ( 4 S 3/2 → 4 I 15/2 ) and red ( 4 F 9/2 → 4 I 15/2 ) up-conversion PL emission under the excitation with a 980 nm diode laser. With increasing Yb 3+ concentration red up-conversion PL intensity increases more rapidly with respect to green emission, because red up-conversion PL intensity strongly depends on Yb 3+ concentration, i.e. 4 F 9/2 state of Er 3+ is directly excited by energy transfer from excited Yb 3+ .