Multiple ratiometric nanothermometry operating with Stark thermally and non-thermally-coupled levels in upconverting Y2−xMoO6:xEr3+ nanoparticles

Abstract

Contactless optical nanothermometers of high thermal sensitivity are in great demand in various fields. In this work, we applied a facile sol-gel method to synthesize a series of Y2-xMoO6:xEr3+ upconverting nanoparticles (UCNPs), capable of acting as luminescence nanothermometers. Upon 980 nm laser light irradiation, with increasing Er3+ content, the prepared samples show a color-tunable upconversion emission, from green to yellow. Comparison of the thermometric properties determined by the Stark thermally coupled levels (TCLs) with those determined by the Stark non-thermally coupled levels (non-TCLs) showed that the superior thermal sensitivity (maximal Sr = 2.063%K−1 at 303 K) is achieved for the non-TCLs 4F9/2(1)/4S3/2(1). Moreover, a higher content of Er3+ in UCNPs (Y1.88MoO6:0.12Er3+ UCNPs) has been found to lead to a significant increase of Sr (Sr MAX = 2.460%K−1 at 303 K). Y2-xMoO6:xEr3+ UCNPs are promising materials for contactless nanothermometers of high sensitivity.