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

Abstract

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 μm) 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 μm, weak blue (~0.41 μm, 2H9/2 → 4I15/2), strong green (~0.56 μm, 2H11/2, 4S3/2 → 4I15/2), and red (~0.67 μm, 4F9/2 → 4I15/2) emission bands were observed as well as weak near‐infrared emissions at 0.8 μm (4I9/2 → 4I15/2) and 0.85 μm (4S3/2 → 4I13/2) at room temperature. The upconversion luminescence properties under ~1.5 μm pumping were further investigated through pump power dependence and decay time studies. Sequential two‐photon absorption leads to the 4I9/2 upconversion emission, whereas energy‐transfer upconversion is responsible for the emission from the higher excited states 2H9/2, 2H11/2, 4S3/2, and 4F9/2. The enhanced red emission with increasing Er3+ concentration most likely occurred via the cross‐relaxation process between (4F7/2 → 4F9/2) and (4I11/2 → 4F9/2) transitions, which increased the population of the 4F9/2 level.