Double-doped YVO₄ nanoparticles as optical dual-center ratiometric thermometers

Crystalline inorganic nanoparticles doped with rare earth ions are widely used in a variety of scientific and industry applications due to the unique spectroscopic properties. The temperature dependence of their luminescence parameters makes them promising candidates for self-referencing thermal sensing. Here we report single phase YVO₄ nanoparticles doped with different pairs of rare earth ions (Nd³⁺/Er³⁺, Tm³⁺/Er³⁺ and Nd³⁺/Tm³⁺) for contactless ratiometric thermometry within a wide temperature range of 298-573 K. The presence of dual luminescence centers in the optical thermometer allows one to circumvent the fundamental limitation of sensitivity inherent to thermometers based on thermally coupled levels. Important parameters for temperature sensing, such as relative thermal sensitivity and temperature resolution, were calculated for all synthesized samples and compared with the literature data. The YVO₄:Tm³⁺,Er³⁺ sample displayed a relative sensitivity of 0.28% K^-1 at room temperature, and the YVO₄:Nd³⁺,Er³⁺ phosphor exhibited a high sensitivity of 0.56% K^-1 at 573 K, while YVO₄:Nd³⁺,Tm³⁺ demonstrated sub-degree thermal resolution. These findings demonstrate the good potential of dual-center ratiometric YVO₄ thermometers and open the way toward future enhancement of their thermometric performances through variation of the doping concentration.