Non‐invasive deep‐tissue temperature monitoring via high‐performance optical nano‐thermometer

Luminescence thermometry with near‐infrared (NIR) emission proves their performance in deeper tissue penetration in biological tissues due to significantly reduced absorption and scattering compared to visible wavelengths. Herein, Er 3+ ,Tm 3+ co‐doped TiO 2 nanofibers with anti‐thermal quenching behavior have been developed for temperature sensing applications in the first and second biological windows. The temperature dependent luminescence intensity ratio (FIR) of Tm 3+ : 3 H 4 → 3 H 6 and Er 3+ : 4 I 11/2 → 4 I 15/2 electronic transitions demonstrate exceptional sensitivity (Sr = 3.59% K −1 at 298 K) and temperature resolution less than 1 K within 298–398 k temperature range. Validation using intralipid tissue phantom reveals a penetration depth of 17.35 mm, underscoring the material's potential for in vitro applications.