Low temperature reliability and high sensitivity of dual-channel up-conversion thermometry phosphor optimized by heterovalent ions

Poor or absent sensitivity at low temperature, as a vital deficiency of up-conversion (UC) luminescence materials, has been restricting the optimization of temperature sensing performance. Herein, UC luminescence, low temperature sensitivity and reliability were optimized concurrently by first doping Nb⁵⁺ ions in CaWO₄:Er³⁺/Yb³⁺ phosphor. The UC intensity was greatly improved by heterovalent ions (Li⁺/Nb⁵⁺) doping, which was mutually verified with the extended decay life. Simultaneously, near constant sensitivity 0.0070 K⁻¹ was obtained based on the sublevels ²H_11/2(3)/⁴S_3/2(1). Moreover, a high absolute sensitivity 0.0104 K⁻¹ and a high relative sensitivity 0.0243 K⁻¹ based on the separated levels ²H_11/2/⁴S_3/2 were achieved. More importantly, regardless of the strategy, the temperature uncertainty δT at low temperatures was less than 0.5 K, and the new temperature sensor also had good repeatability (3%). The above results indicate that this material is an optical temperature sensor with good application prospect, especially in low temperature demand.