Controlled synthesis and upconversion luminescence of Tm3+-doped NaYbF4 nanoparticles for non-invasion optical thermometry

The Tm3+-doped NaYbF4 upconverting nanoparticles were fabricated by a facile hydrothermal method and they were characterized by X-ray diffraction and transmission electron microscopy as well as upconversion (UC) emission spectrum. Under the irradiation of 980 nm light, the as-prepared samples exhibited bright visible UC emissions originating from the intra-4f transitions of Tm3+ ions. The pump power-dependent UC emission spectra were measured to elaborate the involved UC mechanism. Furthermore, the temperature-dependent fluorescence intensity ratio from the thermally coupled levels (F-3(2),3 and H-3(4)) of Tm3+ ions was obtained to analyze the thermometric performances of the studied compounds. It is evident that the reaction temperature can not only improve the UC emission intensity of the Tm3thorn-doped NaYbF4 upconverting nanoparticles, but also modify its sensor sensitivity. Meanwhile, the maximum sensor sensitivity was found to be as high as 2.1 x 10(-4) K-1 with a wide temperature range of 298-778 K, suggesting its potential application for physiological temperature sensing in biological tissues and cells. Ultimately, the Judd-Ofelt theory was employed to clarify the effect of reaction temperature on the temperature sensitivity. (C) 2018 Elsevier B.V. All rights reserved.