Luminescent nanothermometry using short-wavelength infrared light

Abstract

We analyzed the potentiality of the short-wavelength infrared (SWIR) emissions of different lanthanide ions (Er3+, Tm3+ and Ho3+) embedded in different hosts for luminescence thermometry. The 1.55 μm emission band generated by Er3+ has different Stark sub-levels that can be used in temperature sensing purposes. However, the thermal sensitivity that can be achieved with this emission is relatively low, ranging from 0.06 to 0.15% K−1. In the case of Tm3+, the emissions arising from the 3F4 and 3H4 electronically coupled energy levels are useful for luminescence thermometry, with a linear evolution for the intensity ratio in the biological range as the temperature increases, which simplifies the calibration procedure for luminescent thermometers based on this parameter. When co-doped with Ho3+, an efficient energy transfer between the Tm3+ and Ho3+ ions is generated, that results in a new emission line centered at 1.96 μm that can be also used for luminescence thermometry purposes, with an enhanced thermal sensitivity when pumped at 808 nm. The thermal sensitivities achieved with these doping ions are higher than those obtained with Er3+ and are comparable to those reported previously for some lanthanide-doped materials operating in the visible, and in the I- and II-BWs. We demonstrated the potentiality of these emissions in the SWIR region for luminescence thermometry and imaging in ex-vivo experiments by monitoring the increase of temperature induced in chicken breast meat, with an experimental thermal resolution of ∼0.5 K, below the theoretical value of 0.8 K predicted for particles operating in this spectral region, and a penetration depth of at least 0.5 cm.