Enhancing temperature sensitivity of Er³⁺-Yb³⁺ doped NaGd(MoO₄)₂ via particle spacing and crystallinity optimization

Upconversion nanoparticles have emerged as promising materials for non-contact temperature sensors due to their unique detection capabilities and low interference, so it is valuable to explore simple and effective approaches to enhance the temperature measurement sensitivity. In this study, we employed a special sol-gel method to prepare NaGd(MoO₄)₂ powder by calcining the precursor mixture, and the fluorescence properties as well as thermal sensitivity were investigated. Analysis based on XRD, SEM and energy transfer modes revealed that the enhancement in temperature sensitivity resulted from the increased distance between the sensitizer and activator ions as well as changes in crystallinity, compared with normal sol-gel method. By optimizing the doping of rare earth ions, the highest sensitivity reached 3.34 %K⁻¹. Additionally, fluorescence spectra analysis of NaGd(MoO₄)₂ samples synthesized via different methods demonstrated that energy transfer between the sensitizer and activator ions can be achieved through high-temperature calcination. Moreover, LiGd(MoO₄)₂ samples prepared using the unique sol-gel method exhibited similar enhancements in temperature sensitivity as NaGd(MoO₄)₂ powder. These findings imply that the samples prepared through the unique sol-gel synthesis method exhibit significant potential in terms of their fluorescence and temperature detection capabilities.