NIR-NIR upconverting optical temperature sensing based on the thermally coupled levels of Yb3+-Tm3+ codoped Bi7F11O5 nanosheets

摘要

The upconversion of near-infrared (NIR) fluorescence, with a high tissue penetration depth, possesses a distinct advantage in biological temperature detection but is limited by the lack of rare earth-doped nanophosphors with intense and selective NIR UC emission. Here, we show that high-efficiency NIR temperature sensing can be achieved by appropriately doping Tm3+ activators into a polarized layered host, utilizing the high environmental sensitivity of the H-3(4)-> H-3(6) electric dipole transition (808 nm) of Tm3+. To confirm this concept, Yb3+/Tm3+ codoped Bi7F11O5 upconverting nanosheets were synthesized and characterized. Furthermore, the thermometric performance of the samples was analyzed based on the temperature-dependent fluorescence intensity ratio from the thermally coupled levels (F-3(3)/H-3(4)) of Tm3+. The results showed that, under 980 nm diode laser excitation, the prepared samples can produce a high NIR-to-visible UC emission ratio (I-800nm/I-475nm) of over 2000 for Tm3+. The maximum sensitivity Sa/Sr was 1.4% K-1/0.577 K-1 at 303 K based on the F-3(3) and H-3(4) levels, and the material exhibited a wide functional temperature range of 303-573 K. The results of our work not only improve the understanding of the optical properties of RE(3+)n ions in layered materials but also show a potential application for physiological temperature sensing in biological tissues and cells.