Optical thermometry based on near-infrared luminescence from phosphors mixture*

Luminescence ratiometric thermometry based on rare earth (RE) ions has attracted great interest for the potential applications in many fields. But the improvement of the measurement sensitivity and accuracy is significantly restricted due to the small energy gap between thermally coupled levels (TCL). Here, a strategy striving for good thermometric properties of luminescent materials was designed by using the phosphors mixture composed of NaY(WO4)2:Nd3+-Yb3+ and NaY(WO4)2:Er3+, which were prepared by secondary sintering method. Under the excitation of 980 nm laser, the near-infrared (NIR) emissions (710 -920 nm) from Nd3+ ions are effectively strengthened when the temperature increases from 304 to 773 K, whereas Er3+ NIR luminescence centered at around 1536 nm is thermally quenched. The remarkably different response of NIR emissions to the thermal variation allows us to map temperature through the ratiometric method. By optimizing the dopant concentration of rare earth (RE) ions, a maximum sensitivity of 5.14%/K together with a measurement uncertainty of about 0.1 K is acquired at 304 K, which is superior to the previously reported RE luminescence-based temperature sensors, indicating that the approach developed here can pave the way for achieving optical thermometry with desired properties.