We report on the potential application of NIR–to–NIR Nd³⁺-doped yttrium vanadate nanoparticles with both emission and excitation operating within biological windows as thermal sensors in 123–873 K temperature range. It was demonstrated that thermal sensing could be based on three temperature dependent luminescence parameters: the luminescence intensity ratio, the spectral line position and the line bandwidth. Advantages and limitations of each sensing parameter as well as thermal sensitivity and thermal uncertainty were calculated and discussed. The influence of Nd³⁺ doping concentration on the sensitivity of luminescent thermometers was also studied.

We report systematic study of Dy³⁺-doped YVO₄ nanophosphors synthesized via modified Pechini technique. Effect of calcination temperature and doping concentration on structure and luminescence has been investigated. XRD and Raman spectroscopy revealed preparation of single phase nanoparticles without any impurities. Synthesized nanopowders consisted of weakly agglomerated nanoparticles with average size about 50 nm. Photoluminescence spectra of YVO₄:Dy³⁺ nanoparticles consisted of the characteristic narrow lines attributed to the intra-configurational 4f-4f transitions dominating by the hypersensitive ⁴F_9/2–⁶H_13/2 transition. The calcination temperature variation did not affect ⁴F_9/2 lifetime, whereas increase of doping concentration resulted in its gradual decline. Potential application of YVO₄:Dy³⁺ 1 at.% and 2 at.% nanopowders as ratiometric luminescence thermometers within 298–673 K temperature range was tested. The main performances of thermometer including absolute and relative thermal sensitivities and temperature uncertainty were calculated. The maximum relative thermal sensitivity was determined to be 1.8% K⁻¹@298 K, whereas the minimum temperature uncertainty was 2 K.

The development of new contactless thermal nanosensors based on a ratiometric approach is of significant interest. To overcome the intrinsic limitations of thermally coupled levels, a dual activation strategy was applied. Dual activation was performed using co-doped single nanoparticles and a binary mixture of single-doped nanoparticles. Co-doped and mixed YVO₄:Nd³⁺/Eu³⁺ nanoparticles were successfully demonstrated as luminescent nanothermometers and their thermometric performance, in terms of thermal sensitivity, temperature resolution and repeatability, was studied and compared.

Single-phase Ln ³⁺ -doped YVO ₄ nanophosphors demonstrated accurate luminescence thermal sensing by monitoring LIR, spectral position and bandwidth.