Enhancing Optical Thermometric Sensitivity Through Controlling Particle Size in LaNbO4: Yb3+, Tm3+ Up-Converting Luminescent Nanoparticles

Low phonon energy provides new and exciting chances for rare earth niobate crystals to become viable host material in up-conversion luminescence temperature measurement. In this work, the modified molten salt method was used for successfully preparing Yb3+/Tm3+ Co-doped LaNbO4 nanoparticles. The controllable preparation of nanoparticles with different sizes were realized by optimizing the material synthesis process parameters, which effectively enhanced the temperature measurement sensitivity of the nanoparticles. The measurement results demonstrate that the sensitivity of the temperature sensor improves from 0.0204 to 0.024 K− 1 with the size of LaNbO4: Yb3+/Tm3+ nanoparticles decreasing from 140 to 100 nm. As the size of the nanocrystalline particles decrease, the proportion of luminescent active ions located on the surface of the nanoparticle increases. The luminescent ions located on the surface of the nanoparticles play a dominant position in the process of heat exchange with the environment, exhibit higher thermometric sensitivity. The excellent temperature resolution ability (0.027 K) are realized at 210 K. In summary, Yb3+/Tm3+ Co-doped LaNbO4 nanoparticles are great potential candidates for temperature measurement.