Luminescence thermometry of a NdIII and NdIII/YbIII imidazole derived-based MOFs: thermally enhanced ytterbium emission

Abstract

Lanthanides' luminescent thermometry operating in biological windows highlights its promising applications, constantly improving performances, and interesting new findings. This work presents two MOFs, a homometallic sample based on neodymium (1) and a heterometallic one including ytterbium cations (2) as thermometers in the physiological temperature range, operating in biological windows (BWs). These materials were developed with the aim of understanding their thermometric performance and to gain deep knowledge into the energy transfer between the mentioned cations. The homometallic sample achieved a maximum relative sensitivity (Sr) of 0.59%K-1 at 20°C by using the luminescence intensity ratio (LIR) of the two components that contribute to the main emission band ca. 1060 nm, which is associated with the 4F3/2 → 4F11/2 transition. In the case of the heterometallic sample, interestingly, there is an increase in the intensity of the ytterbium cation emission as the temperature increases. This behavior was rationalized by means of theoretical calculations and matches other examples from the literature. The YbIII/NdIII intensity ratio achieves a maximum Sr 0.53%K-1 at 20°C.