Optical Temperature Sensor Using Infrared-to-Visible-Frequency Upconversion in Er ³⁺/Yb ³⁺−Codoped Bi₃TiNbO₉ Ceramics

An optical temperature sensor based on infrared-to-visible upconversion emission in Er³⁺/Yb³⁺ co−doped Bi₃TiNbØ₉ (BTN) ceramics is reported. The fluorescence intensity ratio of the green upconversion photoluminescence (UC−PL) around 524 nm and 545 nm depends on temperature. The operating temperature range and the maximum sensitivity of Er³⁺/Yb³⁺ co−doped Bi₃TiNbO₉ ceramics are 123–693 K and 0.0032 K⁻¹, respectively. BTN:Er³⁺/Yb³⁺ ceramic has good thermal, physical and chemical stability, great UC−PL intensity and low cost fabrication. The results imply that Er³⁺/Yb³⁺ co−doped Bi₃TiNbO₉ ceramic is promising for applications in wide-temperature-range sensors.