A sensitive near infrared to near-infrared luminescence nanothermometer based on triple doped Ln -Y₂O₃

In recent years, luminescence nanothermometers with near infrared light (NIR) emission excited in the NIR range have attracted much attention due to their potential in bio applications. Here, we propose a new nanothermometer based on triple doped 1%Ho, 1%Er, 1%Yb - Y₂O₃ that operates in the second and third biological windows around 1200 and 1530 nm under pulsed excitation at 905 nm. The NIR emissions were analysed in the temperature range of 298–473 K in terms of intensity, shape and dynamics. The nanothermometer performances were described using the luminescent intensity ratio (LIR) corresponding to the ⁵I₆-⁵I₈ and ⁴I_13/2-⁴I_15/2 emissions transitions of Ho and Er, respectively. A maximum relative sensitivity of 1.5% K⁻¹ was achieved at 309 K, which is among the highest five values reported so far for the NIR to NIR downconversion nanothermometers. The thermometer performance for biological application was assessed in terms of nanothermometer reliability and stability as well as emission shape changes induced by water and custom designed optical phantoms. Combination between use of pulsed excitation and identification of Ln doping configuration offering both excitation and emission in the biological windows represent a solid approach that can be easily translated to other hosts to develop a new class of near infrared nanothermometers. (paper)