AUTHOR=Li Liang , Hao Haoyue 

TITLE=Florescence Intensity Ratio Thermometer in the First Biological Window Based on Non-Thermally Coupled Energy Levels of Tm3+ and Ho3+ Ions

JOURNAL=Frontiers in Materials

VOLUME=Volume 8 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2021.767812

DOI=10.3389/fmats.2021.767812

ISSN=2296-8016

ABSTRACT=In this work, the up-conversion luminescence and optical temperature sensing properties of Ho3+/Tm3+/Yb3+ co-doped NaLuF4 phosphors were investigated. The visible (475, 540 and 650 nm) and near-infrared light (692 and 800 nm) radiated from 1Ho3+/4Tm3+/Yb3+ co-doped NaLuF4 phosphors were obvious enough for subsequent detection. The slops in the lnI-lnP plot of the emissions located in first biological window (650, 692 and 800 nm) were both ~1.5, which meat that the power had little effect on the three fluorescence peak ratios. Based on the florescence intensity ratio (FIR) of 650 and 692 nm, the relative sensing sensitivity reach 0.029 K-1 (476 K). The  relative sensing sensitivity based on the FIR of 800 and 692 nm reaches 0.0076 K-1 (476 K). The results reveal that 1Ho3+/4Tm3+/Yb3+ co-doped NaLuF4 phosphors have potential applications in FIR-based temperature sensing in biological tissue for their high sensing sensitivity. In addition, the emission colors of the sample stabilize in the white light region as the temperature increasing from 303 to 467 K, implying that it can also be used in white display.