Fluorescence intensity ratio (FIR) of rare earth ions has been widely used in real-time and accurate temperature sensing because of its superiority of rapid response, self-reference, and noncontact in recent years. However, the energy gap (ΔE) restriction of thermally coupled levels (TCLs) has hindered the sensitivity and practical use of such detectors. Herein, we investigate the FIR thermometry based on nonthermally coupled levels (NTCLs) of rare earth ions for fabricating a sensitive, precise temperature detector. Compared with the traditional FIR thermometry based on TCLs (TCL-FIR), the designed NTCL-FIR sensing thermometry exhibits a series of excellent performance including extremely low temperature uncertainty (∼0.27 K), an ultrahigh temperature sensitivity (>10% K-1), and satisfactory signal recognition ability. The rise of sensitivity and recognition is attributed to breaking the ΔE restriction of TCLs by using an Arrhenius equation. The proposed ideas and methods of NTCL-FIR sensing thermometry can not only improve the performance of temperature sensing devices but also more importantly contribute to the practical development of rare earth ions.
Keywords: fluorescence intensity ratio; nonthermally coupled levels; temperature sensing.