Luminescence intensity ratio squared—A new luminescence thermometry method for enhanced sensitivity

Abstract

In response to the sensitivity limitation of ratiometric luminescence thermometers, herein we propose a novel temperature readout, which exploits two pairs of thermalized energy levels in trivalent lanthanide ion-activated phosphors, to provide significantly enhanced sensitivity. This method is called the luminescence intensity ratio squared (LIR2) method. It is a combination of the dual-excitation single emission band ratiometric (SBR) and conventional (Boltzmann) luminescence intensity ratio (LIR) techniques. The relative sensitivity of LIR2 is the sum of the sensitivities of each method, and its thermal dependence is predicted theoretically. We explain the LIR2 method in detail and identify the perspective of lanthanide-activated probes. The performance of the proposed approach was evaluated using YVO4:Eu3+ and YNbO4:Eu3+ powders and compared with those of the SBR and LIR techniques. The LIR2 method displayed significantly better thermometric performance than SBR and LIR over a wide temperature range (300–850 K).