Multimode Ultrasensitive Optical Temperature Sensing Based on Upconversion Luminescence in BaNb2O6 Phosphor

Multimode and highly sensitive optical temperature measurements are the key technology to improve the temperature monitor. In this work, doping-concentration-optimized BaNb₂O₆ materials show excellent temperature measurement performance, achieving multimode temperature measurement with self-calibration function upon a 980 nm laser diode pump. Four models of optically ultrasensitive temperature measurement are achieved in BaNb₂O₆: Yb³⁺/Er³⁺ and Yb³⁺/Ho³⁺ phosphors by making use of thermal coupling energy levels (Er³⁺: ²H_11/2/⁴S_3/2 and Ho³⁺: ⁵F₅) and nonthermal coupling energy levels (Er³⁺: ²H_11/2/⁴S_3/2, ⁴F_9/2 and Ho³⁺: ⁵F₅, ⁵F₄/⁵S₂). In the BaNb₂O₆: 7.0% Yb³⁺/5.0% Er³⁺ sample, we obtained maximum relative sensitivities (S_r) of S_r-g = 1.64% K^–1 and S_r-Er = 1.48% K^–1 at 298 K and maximum absolute sensitivities (S_a) of S_a-g = 0.33% K^–1 and S_a-Er = 0.113% K^–1 at 573 K corresponding to thermal coupling and nonthermal coupling energy levels, respectively. In the BaNb₂O₆: 7.0% Yb³⁺/0.5% Ho³⁺ sample, maximum S_r levels of S_r-r = 0.64% K^–1 and S_r-Ho = 1.39% K^–1 at 298 K and maximum S_a levels of S_a-r = 0.375% K^–1 (298 K) and S_a-Ho = 1.25% K^–1 (498 K) are obtained simultaneously. Throughout all the modes in the testing temperature range, excellent temperature resolution is exhibited, achieving an optimal value of 0.016 K. The four optical temperature sensors are validated to own excellent resolution, repeatability, and accuracy. All the studies demonstrate that BaNb₂O₆ is a promising candidate in the field of high-precision self-referencing multimode optical temperature measurements.