Size influence on temperature sensing of erbium-doped yttrium oxide nanocrystals exploiting thermally coupled and uncoupled levels' pairs

The performance of Y2O3 nanocrystals with three distinct sizes, doped with 2 mol% of Er3+ ions, as nanothermometers, exploiting two different methodologies is investigated. We found that the sensitivity of the temperature sensor using such crystals is high and this magnitude depends strongly on the crystallite size. For nanothermometers based on fluorescence intensity ratio (FIR) from thermally coupled levels (2H11/2, 4S3/2), the sensitivity is higher for larger nanocrystals. On the other hand, when using FIR from levels which are not thermally coupled (2H11/2, 4F9/2), highest sensitivities were obtained for the smaller nanocrystals. Moreover, the values of absolute and relative sensitivities measured for these samples are among the highest reported so far in literature. These results indicate that Er3+-doped Y2O3 nanocrystals are promising materials for temperature sensing in nanoscale and that the choice of nanocrystals' size and FIR methodology may improve the sensing performance aiming a specific application.