Yb³⁺/Tm³⁺/Ho³⁺ tri-doped YPO₄ submicroplates: A promising optical thermometer operating in the first biological window

Currently, real-time and accurate temperature monitoring of biological tissues and cells is of significance for many biological applications. Here, a new type of optical thermometer have been designed based on the thermo-responsive fluorescence intensity ratio (FIR) of Ho³⁺ (⁵F₅ → ⁵I₈) to Tm³⁺ (³F₃ → ³H₆) emission. To explore the possible application in optical thermometry, Yb³⁺/Ho³⁺/Tm³⁺ tri-doped YPO₄ submicroplates have been successfully synthesized via a facile hydrothermal route. Interestingly, the as-designed UC thermometer (operating in the first biological window) exhibits high temperature sensitivity (∼8.85% K⁻¹) and good signal discriminability, which may be expected to find promising potential application for accurately detecting temperature of biological tissues.