Lifetime of the ³H₄ Electronic State in Tm³⁺-Doped Upconverting Nanoparticles for NIR Nanothermometry

Emission bands from thermally coupled states in lanthanide-doped nanoparticles have been studied for ratiometric nanothermometry in biological applications. Unfortunately certain factors such as water absorption distort the intensity, limiting the accuracy of ratiometric nanothermometry. However, the decay time of such states does not suffer from such distortions. We introduce the decay time of the ³H₄ state in Yb³⁺, Tm³⁺-doped nanoparticles for improved nanothermometry. The strong 800 nm upconversion emission exists in the first biological transparency window. This is the first use of a single upconversion band for lifetime nanothermometry.