Strategy for thermometry via Tm3+-doped NaYF4 core-shell nanoparticles

Optical thermometers usually make use of the fluorescence intensity ratio of two thermally coupled energy levels, with the relative sensitivity constrained by the limited energy gap. Here we develop a strategy by using the upconversion (UC) emissions originating from two multiplets with opposite temperature dependences to achieve higher relative temperature sensitivity. We show that the intensity ratio of the two UC emissions, F-3(2,3) and (1)G(4), of Tm3+ in beta-NaYF4:20%Yb3+, 0.5%Tm-3+/NaYF4:1%Pr3+ core-shell nanoparticles under 980 nm laser excitation exhibits high relative temperature sensitivity between 350 and 510 K, with a maximum of 1.53%K-1 at 417 K. This demonstrates the validity of the strategy, and that the studied material has the potential for high-performance optical thermometry. (C) 2014 Optical Society of America