Highly sensitive optical thermometry through thermally enhanced near infrared emissions from Nd³⁺/Yb³⁺ codoped oxyfluoride glass ceramic

Under 980 nm diode laser excitation, the near infrared (NIR) emissions originated from the ⁴F_7/2/⁴S_3/2 → ⁴I_9/2 (∼750 nm), ⁴F _5/2/²H_9/2 → ⁴I_9/2 (∼803 nm), and ⁴F_3/2 → ⁴I _9/2 (∼863 nm) transitions of Nd³⁺ ions in Nd ³⁺/Yb³⁺ codoped oxyfluoride glass ceramic were obtained and studied as a function of temperature in the range of 303-623 K. It was observed that these NIR emissions were greatly enhanced with the increase of temperature. An explanation based on the luminescence decay curves was given, and it was found that the thermally enhanced phonon-assisted energy transfer (ET) from Yb³⁺ to Nd³⁺ played an important role in such phenomenon. In addition, by using the fluorescence intensity ratio technique, the optical thermometry behavior based on the NIR emissions of Nd³⁺ ions was investigated. Using the 750 and 863 nm emissions from the Nd ³⁺/Yb³⁺ codoped glass ceramic, higher sensitivity for temperature measurement can be achieved compared to the previous reported rare earth ions fluorescence based optical temperature sensors. Due to its thermally enhanced NIR emissions, the Nd³⁺/Yb³⁺ codoped oxyfluoride glass ceramic is a promising candidate for optical temperature sensors with high sensitivity and good accuracy.