Er³⁺/Yb³⁺-Codoped ZrO₂ Nanocrystals as Ratiometric Luminescence Nanothermometers that Cover Three Biological Windows

Aiming to accomplish synchronous optical temperature measurements in the first, second, and third biological windows, this work has carefully designed a novel ratiometric optical thermometer based on ZrO2:Er3+/Yb3+ nanocrystals synthesized by a gel combustion method. Under 980 nm excitation, the luminescence spectra consist of emissions centered at 531, 568, 660, and 1528 nm from Er3+ ions as well as the luminescence located at ∼1000 nm from Yb3+ ions. The temperature-sensing behaviors were investigated on the basis of the valley-to-peak ratio (VPR) technique. Linear temperature dependencies VPR-1 (I668/I682), VPR-2 (I1023/I1036), and VPR-3 (I1492/I1528) were deduced from the homogeneous broadening of the peak line width, showing the advantages of high sensitivity and accuracy. This study provides a novel approach to exploring optical nanothermometers with luminescence covering the three biological windows, which is important in the fields of biology and medicine.