Comparative study on the up- And down-conversion optical ratiometric thermometry in one phosphor

There is a long history of using the Er³⁺ ion's ²H_11/2/⁴S_3/2-⁴I_15/2 transitions for ratiometric thermal sensing. As demonstrated previously, these two transitions can be triggered via up- and down-conversion mechanisms. However, little attention is focused on the influence of these two mechanisms on the sensing performance for the ²H_11/2/⁴S_3/2-⁴I_15/2 transitions. It was demonstrated here the as-prepared CaWO₄:Yb³⁺, Er³⁺ phosphors could be effectively triggered by both the 980 and 405 nm laser diodes to generate the ²H_11/2/⁴S_3/2-⁴I_15/2 transitions via up- and down-conversion mechanisms, respectively. Therefore, up- and down-conversion dual-mode optical thermometry was achieved in one micro-sized thermometer, which allowed us to study the difference between the two methods. Two of the most important evaluating parameters for temperature sensors, e.g., the relative sensitivity and the temperature resolution, were studied and compared upon excitations at 980 and 405 nm. It was confirmed that no obvious difference was observed in these two cases. What's more, it was demonstrated the 980 nm laser diode, compared with the 405 nm one, aroused more heat for the as-prepared samples. It may help us to select proper excitation sources in different situations.