Thulium doped LaF3 for nanothermometry operating over 1000 nm

Abstract

The use and applications of infrared emitting rare-earth luminescent nanoparticles as nanothermometers have attracted a great deal of attention during the last few years. Researchers have regarded rare-earth doped luminescent nanoparticles as appealing systems due to their reliability, sensitivity and versatility for minimally invasive thermal sensing in nanomedicine. The challenge of developing nanothermometers operating over 1000 nm with outstanding brightness and enhanced sensitivity is being constantly addressed. In this sense, this work explores the potential of Tm³⁺ emissions at around 1.23 and 1.47 μm, under excitation at 690 nm, for ratiometric thermometry in Tm³⁺ doped LaF₃ nanoparticles. The temperature dependence of the 1.23 μm emission band, which cannot be observed in systems such as NaNbO₃:Tm, was demonstrated to be very effective and presented a relative thermal sensitivity as high as 1.9% °C⁻¹. The physical mechanisms behind the strong thermal dependences were explained in terms of multiphonon decays and cross-relaxations. As a proof of concept, the nanothermometers presented were capable of accessing the basic properties of tissues in an ex vivo experiment using thermal relaxation dynamics.