Optical thermometry and fingerprint detection in SrLa1−<i>x</i>Eu<i>x</i>LiTeO6 phosphors with abnormal thermal quenching effect

To overcome the sensitivity limitation of conventional luminescence intensity ratio optical thermometers, we designed an optical thermometer using double-perovskite SrLa1-xEuxLiTeO6 phosphors based on abnormal thermal quenching effect. A series of red double-perovskite SrLa1−xEuxLiTeO6 phosphors were synthesized through a facile high-temperature solid-state reaction, and the photoluminescence properties and thermometric behaviors were thoroughly explored. The X-ray diffraction pattern and Rietveld refinement show that the compounds were formed in the monoclinic phase. The UV–visible spectra indicate that the optical bandgaps of the SrLa1−xEuxLiTeO6 (x = 0 and 0.5) phosphors were 3.56 and 3.42 eV, respectively. The optimized dopant concentration for Eu3+ was x = 0.5 with the concentration quenching mechanism of dipole–dipole interaction. Under different excitations, SrLa1−xEuxLiTeO6 phosphors exhibited opposite luminescent intensity variations with increased temperatures. Based on the abnormal thermal quenching phenomenon, the temperature-sensing performances of SrLa0.5Eu0.5LiTeO6 phosphors were extensively investigated using a dual-excitation single-band ratiometric strategy. A maximum relative sensitivity value was determined as 1.21% K−1 at 373 K. Moreover, the fluorescence images of fingerprints developed by SrLa0.5Eu0.5LiTeO6 phosphors were clearly visible, and level I–III detail features were highlighted. These results suggest that SrLa0.5Eu0.5LiTeO6 phosphors are prospective candidates for non-contact optical thermometry and latent fingerprint detection.