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Cubic binary transparent (Er1–x Yb x )2O3 (x = 0.005 and 0.01) ceramics with a high transmittance of ∼78.1% at 600 nm (∼95.6% of the theoretical transmittance of the Er2O3 single crystal) were successfully fabricated by vacuum sintering. Upon 980 nm laser pumping, the (Er1–x Yb x )2O3 ceramics emit characteristic near-infrared downconversion radiation at 1450–1600 nm arising from the 4I13/2 → 4I15/2 transition of Er3+. The upconversion spectra of (Er,Yb)2O3 ceramics present typical red emission at 650–670 nm and green emission at 520–555 nm corresponding to 4F9/2 → 4I15/2 and 2H11/2/4S3/2 → 4I15/2 transitions of Er3+, respectively. A 0.5 at. % Yb3+ dopant dramatically improves the upconversion luminescence intensity by ∼13 times relative to the pure Er2O3 counterpart. The luminescence intensity gradually increases with the rising laser output power, and the upconversion mechanism ascribes to two-phonon processes. The fluorescence lifetimes of the (Er0.995Yb0.005)2O3 ceramic are determined to be ∼19.26 μs for the 540 nm green emission and ∼26.60 μs for the 668 nm red emission. The noncontact optical thermometric ability of the (Er0.995Yb0.005)2O3 ceramic in the temperature range of 298–473 K is assessed using the thermoresponsive fluorescence intensity ratio technique, and the maximum absolute sensitivity is ∼0.0045 K–1.

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