Near-infrared emitting Nd³⁺-Yb³⁺ codoped Y₂O₃ nanocrystals for highly sensitive optical thermometry

Rare earth ions activated nanomaterials have been extensively considered as promising candidates for optical thermometry due to their unique photoluminescence characteristics. Nevertheless, thermally coupled levels-based thermometers are suffering from low sensitivity because of the restriction of small energy gap. Herein, the phonon-assisted energy transfer from Yb³⁺ to Nd³⁺ in Y₂O₃ nanoparticles, which makes the near infrared emissions of Nd³⁺ and Yb³⁺ ions respond to temperature inversely, is utilized to achieve sensitive temperature measurement via the ratiometric method. When pumped by 980 nm continuous wave laser, the multizone thermometry is performed owing to the different dependence of energy transfer on the temperature. The maximum relative sensitivities achieved in the temperature ranges of 423–773 K and 303–333 K are both approximately 2.3% K⁻¹, which are superior to most previously reported luminescence-based temperature sensors. In addition, it is found that the measurement sensitivity is significantly influenced by the laser-induced heating effect especially at relatively low temperatures. Under the excitation of 980 nm square wave laser, the relative sensitivity is enhanced from 2.3% to 2.9% K⁻¹ in the physiological temperature region. These findings can provide an effective pathway to improving the thermometric behavior and expanding the application of luminescence temperature sensing in various fields.