Exploiting Bandgap Engineering to Fine Control Dual-mode Lu2(Ge,Si)O5:Pr3+ Luminescent Thermometers

Abstract

It was proved quite recently that luminescence thermometry may benefit a lot utilizing the 5d→4f/4f→4f intensity ratio of Pr³⁺ transitions. This paper presents a comprehensive study of Lu₂(Ge_x,Si_1-x)O₅:Pr phosphors in the full range of Ge concentrations (x=0–1) for luminescence thermometry. Silicon substitution by germanium allows effective managing their thermometric properties through bandgap engineering. Ge/Si ratio controls the range of temperatures within which the 5d→4f Pr³⁺ luminescence can be detected. This, in turn, defines the range of temperatures where the 5d→4f/4f→4f emission intensity ratio can be utilized for thermometry. Altogether, the bandgap engineering allows widening the operating range of thermometers (17-700 K), fine-tune the range of temperatures with the highest relative sensitivity, and reduce the inaccuracy of the measurements. The kinetics of the 5d→4f luminescence is also controlled by bandgap engineering and can be also used for luminescence thermometry. The Lu₂(Ge_x,Si_1-x)O₅:Pr phosphors were, thus, designed as dual-mode luminescent thermometers exploiting either inter- and intra configurational intensity ratios or the 5d→4f decay time. The highest relative thermal sensitivity, 3.54 % K ^-1, was found at 17 K for Lu₂(Ge_0.75,Si_0.25)O₅:Pr and at 350 K for Lu₂SiO₅:Pr and was combined with a very low (<0.03 K) temperature uncertainty. Herein, we proved that bandgap engineering is a promising and effective approach to develop high-performance luminescence thermometers.