Constructing highly sensitive ratiometric nanothermometers based on indirectly thermally coupled levels

Fluorescence intensity ratio-based temperature sensing with a self-referencing characteristic is highly demanded for reliable and accurate sensing. Lanthanide ions with thermally coupled levels have been widely used for ratiometric temperature sensing. However, these systems suffer from low relative temperature sensitivity and poor luminescence signal discriminability. Herein, the concept of indirectly thermally coupled levels is introduced and employed to actualize high performance temperature sensing. By means of the temperature-dependent phonon-assisted non-radiative relaxation, the I-4(13/2) excited state (with infrared emission) of Er3+ can be indirectly thermally coupled with the S-4(3/2) excited state (with visible emission) under 808 nm or 980 nm excitation. This is experimentally realized in specially designed NaErF4:10Yb@NaYF4 nanocrystals, and the corresponding ratiometric nanothermometer shows excellent luminescence thermal sensing performance with a maximum relative sensitivity value up to 3.76% K-1 at 295 K.

Automated summary

The concept of indirectly thermally coupled levels was introduced in this study to achieve high-performance temperature sensing, utilizing temperature-dependent phonon-assisted non-radiative relaxation to indirectly thermally couple the excited states of Er3+ under certain excitation. This method was experimentally realized in specially designed NaErF4:10Yb@NaYF4 nanocrystals, demonstrating excellent luminescence thermal sensing performance with a maximum relative sensitivity value of up to 3.76% K-1 at 295 K.