Highly sensitive KY3F10: Yb3+/Tm3+ Nanocrystals for Optical Thermometry in the First Biological Window

Abstract

High performance temperature sensor capable of operating within the biological window remains a critical requirement in biomedical applications. In this study, KY3F10: Yb3+/Tm3+ nanocrystals were synthesized by a hydrothermal method and utilized as an optical thermometer in the first biological window. The doping concentrations of both Yb3+ and Tm3+ ions were optimized in order to enhance the luminescence intensity. Results show that the 3F2,3→3H6 emission (~ 700 nm) is strongly dependent on Tm³⁺ concentration due to cross relaxation processes and the optimum content was determined to be 0.5 mol%. The sample of KY3F10: 10% Yb3+/0.5% Tm3+ was selected for detailed optical thermometry study based on the fluorescence intensity ratio (FIR) technique. Utilizing the 3F2,3→3H6 and 1G4→3F4 energy levels (I700/I652) of Tm3+ ions, the maximum absolute sensitivity (SA,max) and relative sensitivity (SR,max) values are achieved as 0.067 K-1 and 3.301 %K−1, respectively. These results surpass many previously reported FIR-based temperature sensors operating within the biological windows. Additionally, the temperature sensing behavior of I700/I480 was also investigated, yielding SA,max and SR,max values of 0.0386 K-1 and 1.685 %K−1, respectively. These findings demonstrate that KY3F10: Yb3+/Tm3+ nanocrystals are a promising candidate for broad-range vis-NIR optical thermometry.