Influence of excitation and detection geometry on optical temperature readouts – reabsorption effects in luminescence thermometry

Abstract

The technology of lanthanide-based luminescent thermometers enabling remote optical temperature measurements is intensively developed. Sensors that allow the most precise, remote temperature readouts can be successfully used in biological, electronic, engineering and industrial processes. This work analyses the often-underestimated effect of excitation and detection geometry, as well as the sample thickness on the spectroscopic properties of the material and performance of the resulting luminescent thermometers. In the case of thick-layer samples, a significant change in the luminescence intensity ratios was observed compared to the thin-layer counterparts. This resulted in varying values of absolute and relative sensitivities for different sample thicknesses. The observed changes are assigned to a reabsorption effect, which is particularly significant for the thick-layer samples examined in the transmission (back-illuminated) geometry. The results presented in this work have very important implications on the accuracy of optical temperature monitoring via luminescence thermometry with Er³⁺ ions.