Strong red upconversion luminescence and optical thermometry of In2O3: Er3+, Yb3+ phosphor

Er³⁺ ions and Yb³⁺ ions co-doped indium oxide (In₂O₃) phosphors were successfully synthesized by high temperature solid phase method. At 980 nm laser excitation, the phosphor has weak 552 nm green and strong 661 nm red emission bands. And the upconversion luminescence (UCL) intensity of red light is significantly stronger than that of green light. They are attributed to the ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively. And the optimal sample is In₂O₃: 4 % Er³⁺, 10 % Yb³⁺. The appearance of phosphor was observed by field emission scanning electron microscopy. The UCL of phosphor is a two-photon process based on power dependence. In addition, photoluminescence excitation spectra and down-conversion luminescence spectra are used to explain the luminescence mechanism. The temperature sensing property of the phosphor in the temperature range of 348 K–598 K were tested. The sensitivity were obtained by fluorescence intensity ratio (FIR). The fit degree of FIR is 0.9936. It achieves a maximum relative sensitivity of 0.73 % K⁻¹ at 348 K and a maximum absolute sensitivity of 0.039 K⁻¹ at 373 K. In₂O₃: Er³⁺, Yb³⁺ phosphors with high quality luminescence and excellent sensitivity have important application value in non-contact temperature measurement.