Near infrared to visible upconversion of Er3+ in CaZrO3/CaSZ eutectic crystals with ordered lamellar microstructure

In this work we report the near infrared to visible upconversion luminescence of Er3+ ions in CaZrO3/CaSZ eutectic crystals with ordered lamellar microstructure. The microstructure consists of alternating 2-μm-thick lamellae of calcia-stabilized zirconia (CaSZ) and calcium zirconate (CaZrO3) single crystals. Er3+ ions enter both phases but at a higher concentration in CaSZ. Wavelength selective excitation along the 4I15/2→4I9/2 absorption band allows to distinguish the upconverted emission from Er3+ sites in the two eutectic phases. In the CaZrO3 phase the upconversion emission spectrum is dominated by an intense green emission characterized by sharp (2H11/2,4S3/2) levels together with a more weak red emission from 4F9/2 level. In the CaSZ phase, a broad green and red emissions occur with an enhancement of the red emission from level 4F9/2. These upconverted emissions are attributed to a two photon process. The excitation wavelength dependence of the upconverted luminescence together with its time evolution after infrared pulsed excitation suggest that energy transfer upconversion processes are responsible for the upconversion luminescence.