Anti-Stokes excited Er³⁺/Yb³⁺ codoped oxyfluoride glass ceramic for luminescence thermometry

Luminescent materials doping with rare earth ions have demonstrated the potentiality as sensitive thermometers in many fields. Nevertheless, the excitation lasers induced heating (LIH) effect, which is always involved in the thermometry process, significantly limits the measurement accuracy. In this work, the LIH effect is resolved in 1.064 µm continuous wave laser excited Er³⁺/Yb³⁺ codoped oxyfluoride glass ceramic. Through the fluorescence intensity ratio (FIR) technique, optical temperature sensing via the green upconversion luminescence from Er³⁺ ions was investigated. Thermally enhanced upconversion emissions were observed as the temperature was increased from 309 to 573 K. More importantly, the FIR was hardly influenced by changing the pumping power densities, indicating stable and accurate temperature sensing could be achieved by nonresonant excited Er³⁺/Yb³⁺ codoped oxyfluoride glass ceramic without the complications from laser induced thermal effect. Combining with the steady-state rate equations and temperature dependent luminescence decay curves, theoretical analysis was performed and the results illustrate that multi-phonon assisted anti-Stokes excitation process of Yb³⁺ plays a key role in the excellent sensing characteristics.