Gd2O3:Er3+,Yb3+ Upconversion Nanoparticle-Based Thermometry for Temperature Monitoring

Noncontact optical nanothermometry on the basis of fluorescence intensity ratio (FIR) has shown huge prospect in scientific research and real life owing to its excellent detection accuracy, rapid response, and weak environment dependence. However, the poor sensitivity still restricts practical application. Herein, a thermometry strategy using the synergistic effects of diversity in the thermal behavior of Er3+ and inverse fluorescence intensity ratio was proposed in Gd2O3:Er3+,Yb3+ nanospheres. Employing this strategy, the absolute sensitivity was dramatically enhanced. Importantly, the maximum absolute sensitivity of about 64% at 298 K was obtained in the level pair F-4(9/2)/H-2(11/2(1)) for the Gd2O3:1 mol % Er3+,10 mol % Yb3+ nanospheres. The mechanism analysis proved that the superior sensitivity was attributed to the large Boltzmann effect of stark sublevels and temperaturedependent nonradiative transition process of red emission. Meanwhile, controllable tuning of absolute sensitivity for the coupled pair F-4(9/2)/H-2(11/ 2(1)) was achieved by altering Yb3+ concentration. Furthermore, except excellent sensitivity, the outstanding signal discriminability (Delta E = 135 nm) was simultaneously implemented. These findings not only provided a common approach to improve absolute sensitivity but also surmounted the limitations of conventional thermally coupled level (TCL)-based optical thermometry.