167 / 2024-06-14 10:01:46

Tri-modal ratiometric luminescent thermometer covering entire Near-infrared transparency windows

Rare earths, luminescence intensity ratio, near-infrared

Luminescence intensity ratio (LIR) thermometers have aroused great interest in recent research due to their high spatial resolution, superior precision and fast response, which can avoid the defects of traditional contact sensors including low spatial, thermal and temporal resolution. In addition, LIR thermometers enable non-invasive measurements in vivo without physical contact between the observers and target analytes. However, the current LIR thermometers focus on the visible range (400–650 nm), which suffer from limited penetration depth in biological tissues. Herein, a multimode LIR thermometer covering all near-infrared (NIR) transparency windows is designed based on Y₃Al₅O₁₂: Cr³⁺/Ln³⁺ (Ln=Ho, Er, Yb) phosphors under 980 nm excitation. The Cr³⁺/Ln³⁺-activated up-conversion emissions provide a proportional luminescence thermometer in NIR-I mode by virtue of the energy transfer between Cr³⁺ ions and Ln³⁺ ions. The downshifting emissions of Er³⁺/Ho³⁺ are applied to the LIR thermometry in NIR-III/II mode. Under the influence of the crystal field, the emission spectrum of ⁴H_13/2→⁴I_15/2 transition splits into four peaks in NIR-III window, which allows the thermal coupling thermometry of Mode-III. Three modes show distinct thermometric performance in different NIR transparency windows and temperature ranges, and each window contributing to detect deep-tissue temperature in a unique way.