Novel excited-state nanothermometry combining the red-shift of charge-transfer bands and a thermal coupling effect

Abstract

We propose unprecedented excited-state nanothermometry by combining the red-shift of V–O charge-transfer bands from the VO₄³⁻ group and the thermal coupling effect between the ²H_11/2 and ⁴S_3/2 levels of Er³⁺. With increasing temperature, the V–O charge-transfer bands in excitation spectra by monitoring at ²H_11/2 and ⁴S_3/2 levels moved to a longer wavelength, and their excitation intensities showed diametrically opposite trends, which provided two ideal signal acquisition intervals for ratiometric nanothermometers. The relative temperature sensitivity reached as high as 4.7% K⁻¹ at 373 K, which is dominant in the current nanothermometers based on the excited state, and was 6-fold that based on the typical thermally coupled thermometry of Er³⁺. The repeatability was >98.2% and the temperature uncertainty was 0.15 K at 373 K.