Luminescence of any substance is strongly affected by temperature. Therefore, in principle, any material may be utilized to determine temperature from changes in its excitation and emission band energies and bandwidths, emission intensities, ratios of intensities of different emission bands, polarization/anisotropy, emission decay- and rise-times [1, 2]. However, for practical applications in thermometry, materials and material’s systems ought to be thermally and chemically stable, have sufficient brightness and photostability, and their luminescence should notable change with temperature.

Today, lanthanide and transition metal activated phosphors, quantum dots, organic dyes and pigments, and metal-organic complexes and frameworks are common choices for luminescence thermometry probes. Among them, due to compatibility with the biological “optical window” and low interference from light scattering and background fluorescence, those probes emitting in the red and near-infrared parts of the electromagnetic spectrum are of exceptional interest for bio-medical applications.

Here, the focus is on the emission intensity ratio and emission decay based luminescence thermometry methods because they are self-referencing (do not require reference measurements) and are not affected by changes in measurements conditions. The principle of operation of these methods is presented along with corresponding figures of merit. Then, the main red- and NIR-emitting materials utilized for thermometry probes are listed and their performance is discussed. These include Eu³⁺, Nd³⁺, Cr³⁺ and Mn⁴⁺ activated phosphors, PbSe, PbS, CdSe/ZnS and PbS/CdS/ZnS core–shell, ZnS−AgInS₂ alloy, ZnS:Mn²⁺, CsPbCl3:Mn²⁺ quantum dots, and organic Pluronic F127–Cy5.5 hybrid probe and metal-organic Eu_0.0069Tb_0.9931-2,5-dimethoxy-1,4-benzenedicarboxylate probes. Finally, several examples of multifunctional applications of these probes and methods is shown, such as in combined bio-imagining and thermal sensing, photothermal therapy and combined physical and chemical sensing.

References:

1. M.D. Dramićanin, Luminescence Thermometry: Methods, Materials, and Applications 1ed, Elsevier Ltd, ISBN: 978-0-08-102029-6, 2018.
2. M.D. Dramićanin, Sensing temperature via downshifting emissions of lanthanide-dopedmetal oxides and salts. A review, Methods Appl Fluoresc 4 (4) (2016) 23. 42001.