NIR to Visible Upconversion in Nanocrystalline and Bulk Lu2O3:Er3+

In this paper we investigate the upconversion luminescence of bulk and nanocrystalline Lu 1.98 Er 0.02 O 3 following excitation into the 4 I 11/2 level using 980 nm radiation. After NIR continuous wave excitation, blue, green, and red emissions were observed for both samples under investigation with the green emission dominating the upconversion spectrum. A power study reveals that the 4 S 3/2 (green) and 4 F 9/2 (red) emitting levels are populated via two-photon excited-state absorption (ESA) and energy-transfer upconversion (ETU) processes. Upconversion from the 2 P 3/2 level is attained via a three-step phonon-assisted energy-transfer process. A marked temperature dependence of the excited-state lifetimes in both the bulk and nanocrystalline samples was evidenced.