Near-Infrared and Upconversion Luminescence in Er:Y2O3 Ceramics under 1.5 μm Excitation

Results of the spectroscopic characteristics and upconversion luminescence in Er3+ doped yttria (Y2O3) transparent ceramics prepared by a modified two-step sintering method are presented. The near-infrared (1.5 mu m) luminescence properties were evaluated as a function of Er3+ concentration. Judd-Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er3+-doped Y2O3 single crystal and nanocrystals. Following pumping at 1.532 mu m, weak blue (similar to 0.41 mu m, H-2(9/2) -> I-4(15/2)), strong green (similar to 0.56 mu m, H-2(11/2), S-4(3/2) -> I-4(15/2)), and red (similar to 0.67 mu m, F-4(9/2) -> I-4(15/2)) emission bands were observed as well as weak near-infrared emissions at 0.8 mu m (I-4(9/2) -> I-4(15/2)) and 0.85 mu m (S-4(3/2) -> I-4(13/2)) at room temperature. The upconversion luminescence properties under similar to 1.5 mu m pumping were further investigated through pump power dependence and decay time studies. Sequential two-photon absorption leads to the I-4(9/2) upconversion emission, whereas energy-transfer upconversion is responsible for the emission from the higher excited states H-2(9/2), H-2(11/2), S-4(3/2), and F-4(9/2). The enhanced red emission with increasing Er3+ concentration most likely occurred via the cross-relaxation process between (F-4(7/2) -> F-4(9/2)) and (I-4(11/2) -> F-4(9/2)) transitions, which increased the population of the F-4(9/2) level.