Upconversion processes of Er 3+ in ZrO 2 -CaO eutectic crystals

In this work we report the infrared to visible upconversion luminescence in Er 3+ -doped ZrO 2 -CaO eutectic crystals with an ordered microstructure. The microstructure consists of alternating 2 μm thick lamellae of calcia-stabilized zirconia (CaSZ) and CaZrO 3 crystals. Er 3+ ions enter both phases but at a higher concentration in CaSZ. Site selective excitation at different wavelengths along the 4 I 15/2 → 4 I 9/2 absorption band allows to select the upconverted emission from Er 3+ ions corresponding to the two components of the eutectic samples. Depending on the excitation wavelength the upconversion emission spectrum is dominated either by the CaZrO 3 contribution, with an intense green emission characterized by sharp peaks from ( 2 H 11/2 , 4 S 3/2 ) levels together with a more weak red emission from 4 F 9/2 level, or by the CaSZ phase with broad green and red emissions with an enhancement of the red emission from level 4 F 9/2 . The possible upconversion mechanisms are discussed in terms of excitation power dependence and lifetimes of the upconversion emissions.