Highly sensitive optical ratiometric thermal sensing based on the three-photon upconversion luminescence of Y2O3:Yb3+,Er3+ nano-thermometers

Abstract

Highly sensitive optical thermal sensing is achieved here based on the three-photon upconversion luminescence of Y₂O₃:Yb³⁺,Er³⁺ nano-thermometers. In the temperature range of 303–783 K, the ⁴G_11/2 and ²H_9/2 energy levels of Er³⁺ ion embedded in Y₂O₃ nanocrystals are found to be thermally linked. The ⁴G_11/2–⁴I_15/2 and ²H_9/2–⁴I_15/2 transitions’ intensity ratio thus satisfies the Boltzmann distribution. It is demonstrated that the relative sensitivity, on the basis of this ratio for temperature measurement, is as high as 2.05% K⁻¹ at 303 K. It is, to the best of our knowledge, the maximum thermal sensitivity reported so far for the ⁴G_11/2–⁴I_15/2 and ²H_9/2–⁴I_15/2 transitions in various hosts. Moreover, this sensitivity is larger than all previously reported values that depend on the luminescence of the Er³⁺ ion. What's more, this value is also among the highest sensitivities achieved based on other thermally linked states of rare earth ions. As an added benefit, it has been shown that the single ²H_9/2–⁴I_15/2 transition can also be used for optical thermal sensing and its relative sensitivity is up to 1.27% K⁻¹ at 783 K, which is 2.9 times the theoretical maximum sensitivity of ratiometric thermal detection based on the thermally linked states of rare earth ions.