Optical Thermometry Operation within All Three Biological Windows Using Nd³⁺:Er³⁺:Y₂O₃ Nanocomposite Phosphors

The temperature of biological systems is an important parameter to be monitored during metabolic processes and treatment of diseases. In this scenario, optical thermometry generally involves the operation of the temperature sensor within one of the near-infrared biological windows, where light has its maximum depth of penetration. Here we propose a strategy involving lanthanide-doped inorganic nanocomposite phosphors in which the optical temperature sensing operation is feasible within all three near-infrared biological windows using a single thermometric system. Using low-power CW laser excitation at 808 nm, we achieved downshifted luminescence in Nd3+ (transitions 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2) and Er3+ (transition 4I13/2 → 4I15/2) doped in Y2O3 crystalline ceramic powders prepared by combustion synthesis. Using the valley-to-peak luminescence intensity ratio method, we estimated temperature sensitivity parameters to be as high as 0.45% K–1 at 298 K.