Near‐Infrared and Upconversion Luminescence in Er:Y 2 O 3 Ceramics under 1.5 μm Excitation

Results of the spectroscopic characteristics and upconversion luminescence in Er 3+ doped yttria ( Y 2 O 3 ) 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 Er 3+ concentration. Judd–Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er 3+ ‐doped Y 2 O 3 single crystal and nanocrystals. Following pumping at 1.532 μm, weak blue (~0.41 μm, 2 H 9/2 → 4 I 15/2 ), strong green (~0.56 μm, 2 H 11/2 , 4 S 3/2 → 4 I 15/2 ), and red (~0.67 μm, 4 F 9/2 → 4 I 15/2 ) emission bands were observed as well as weak near‐infrared emissions at 0.8 μm ( 4 I 9/2 → 4 I 15/2 ) and 0.85 μm ( 4 S 3/2 → 4 I 13/2 ) 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 4 I 9/2 upconversion emission, whereas energy‐transfer upconversion is responsible for the emission from the higher excited states 2 H 9/2 , 2 H 11/2 , 4 S 3/2 , and 4 F 9/2 . The enhanced red emission with increasing Er 3+ concentration most likely occurred via the cross‐relaxation process between ( 4 F 7/2 → 4 F 9/2 ) and ( 4 I 11/2 → 4 F 9/2 ) transitions, which increased the population of the 4 F 9/2 level.