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+: 2H11/2/4S3/2 and Ho3+: 5F5) and nonthermal coupling energy levels (Er3+: 2H11/2/4S3/2, 4F9/2 and Ho3+: 5F5, 5F4/5S2). In the BaNb2O6: 7.0% Yb3+/5.0% Er3+ sample, we obtained maximum relative sensitivities (Sr) of Sr-g = 1.64% K–1 and Sr-Er = 1.48% K–1 at 298 K and maximum absolute sensitivities (Sa) of Sa-g = 0.33% K–1 and Sa-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 Sr levels of Sr-r = 0.64% K–1 and Sr-Ho = 1.39% K–1 at 298 K and maximum Sa levels of Sa-r = 0.375% K–1 (298 K) and Sa-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.