Modified calculation method of relative sensitivity for fluorescence intensity ratio thermometry.

The calculation method of relative sensitivity (Sr) for fluorescence intensity ratio (FIR) thermometry is discussed, taking the F33-H63 and H43-H63 transitions of Tm3+ as examples. The value of Sr is calculated using its original definition, and is found to largely deviate from the result obtained using the conventional method that is widely used at present. This deviation is found to stem from the neglect of an offset. A modified expression of Sr is proposed, which shows the true performance of FIR technology and makes it possible to precisely compare the Sr values obtained using various methods.