Upconverting NIR-to-NIR LuVO₄:Nd³⁺/Yb³⁺ Nanophosphors for High-Sensitivity Optical Thermometry

Accurate contactless thermometry is required in many rapidly developing modern applications such as biomedicine, micro- and nanoelectronics, and integrated optics. Ratiometric luminescence thermal sensing attracts a lot of attention due to its robustness toward systematic errors. Herein, a phonon-assisted upconversion in LuVO₄:Nd³⁺/Yb³⁺ nanophosphors was successfully applied for temperature measurements within the 323-873 K range via the luminescence intensity ratio technique. Dual-activating samples were obtained by codoping and mixing single-doped nanopowders. The effect of the type of dispersion system and the Yb³⁺ doping concentration was studied in terms of thermometric performances. The relative thermal sensitivity reached a value of 2.6% K^-1, while the best temperature resolution was 0.2 K. The presented findings show the way to enhance the thermometric characteristics of contactless optical sensors.