Abstract: Obtaining non-contact optical temperature sensing materials with good thermal stability and luminescent properties is one of the current research hotspots. In this work, Er³⁺/Yb³⁺ co doped CaGdAlO₄∶Er_x,Yb_0.10(x=0.006, 0.008, 0.010, 0.012, 0.014) single-phase phosphors were prepared by high-temperature solid-state method. For CaGdAlO₄∶Er_x,Yb_0.10 powders with different Er³⁺ doping concentrations, the particle sizes range from 0.6 μm to 4.2 μm. When the samples are under 980 nm laser excitation, there exists two emission bands in the 500~575 nm range and one emission band in the 630~690 nm. The two stronger green emission bands located at 528 and 550 nm, and they could be attributed to ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions, while the weaker red emission band at 663 nm could be attributed to ⁴F_9/2→⁴I_15/2 transition of Er³⁺. The optimal upconversion luminescence intensity was obtained from CaGdAlO₄∶Er_0.010,Yb_0.10. In the temperature range of 300~573 K, based on fluorescence intensity ratio FIR_528/550 parameters, the absolute sensitivity S_A increases from 44.4×10^-4 K^-1(@300 K) to 52.0×10^-4 K^-1(@445 K), and then decreases to 49.0×10^-4 K^-1(@573 K). The relative sensitivity S_R decreases monotonically from 0.95×10^-2 K^-1(@300 K) to 0.27×10^-2 K^-1(@573 K). Furthermore, the heating-cooling cycling experiment shows that the thermal repeatability of temperature sensing for the phosphor is better than 98%. The results demonstrate that CaGdAlO₄∶Er_0.010,Yb_0.10 phosphors have potential applications in the field of optical temperature sensing.

Key words: rare earth ion, phosphor, Er³⁺/Yb³⁺ co doping, upconversion, fluorescence intensity ratio, temperature sensing, high-temperature solid-state method