Boltzmann- and Non-Boltzmann-Based Thermometers in the First, Second and Third Biological Windows for the SrF ₂:Yb ³⁺, Ho ³⁺ Nanocrystals Under 980, 940 and 915 nm Excitations

Abstract

Spectrally determination of temperature based on the lanthanide-doped nanocrystals (NCs) is a vital strategy to noninvasively measure the temperature in practical applications. Here, we synthesized a series of SrF ₂:Yb ³⁺/Ho ³⁺ NCs and simultaneously observed the efficient visible upconversion luminescence (UCL) and near-infrared (NIR) downconversion luminescence (DCL) under 980, 940 and 915 nm excitations. Subsequently, these NCs were further utilized for thermometers based on the Boltzmann (thermally coupled levels, TCLs) and non-Boltzmann (non-thermally coupled levels, NTCLs) of Ho ³⁺ ions in the first (~ 650 nm), second (~ 1012 nm) and third (~ 2020 nm) biological windows (BW-I, BW-II and BW-III) under tri-wavelength excitations. The thermometric parameters including the relative sensitivity ( \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$S_{{\text{r}}}$$\end{document} ) and temperature uncertainty ( \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\delta T$$\end{document} ) are quantitatively determined on the I ₆₄₈/ I ₅₄₁ (BW-I), I ₁₁₈₆/ I ₁₀₁₂ (BW-II), and I ₁₉₅₀/ I ₂₀₂₀ (BW-III) transitions of Ho ³⁺ ions in the temperature range of 303–573 K. Comparative experimental results demonstrated that the thermometer has superior performances.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11671-022-03718-z.